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  • richardmitnick 10:37 am on June 11, 2020 Permalink | Reply
    Tags: "Diving for the Bones of the Ice Age", , , Giant ground sloth's pelvis recovered from Hoyo Negro., Hoyo Negro, Paleontology,   

    From UC San Diego: “Diving for the Bones of the Ice Age” 

    From UC San Diego

    Jun 11, 2020
    Xochitl Rojas-Rocha

    Cave divers carefully maneuver the giant ground sloth’s pelvis through Hoyo Negro. Photo Credit: Sam Meacham, CINDAQ

    For thousands of years, the massive pelvis lay undisturbed at the bottom of the watery black pit. Approximately four feet across and weighing an estimated 80 pounds, it had once belonged to a giant ground sloth, an elephant-sized animal that roamed the ancient Americas alongside the saber-tooth cat and the woolly mammoth.

    Sometime during its life, the sloth lumbered into a labyrinth cave system and wandered until it encountered the subterranean pit known today as Hoyo Negro, or “Black Hole.” Blind in the darkness, the sloth took a fatal step over the edge of the pit and plummeted nearly 100 feet. The impact would have killed it instantly.

    Brett Butler (front center), Jeffrey Sandubrae (left) and other members of the Qualcomm Institute’s Prototyping Lab stand around the cradle that would ultimately carry the giant ground sloth pelvis to the surface. Photo Credit: Alex Matthews, QI

    These days, Hoyo Negro is a morbid treasure trove for paleontologists: a collection of partially fossilized, Ice Age-era skeletons belonging to saber-tooth cats, several species of ground sloths, an extinct species of bear and Naia, a young woman who lived and died approximately 13,000 years ago. Dominique Rissolo, a research scientist and archaeologist with UC San Diego’s Qualcomm Institute (QI), and colleagues have studied their bones for the past eight years to learn more about the region’s history.

    Hoyo Negro. http://hoyonegro.ucsd.edu/

    “The abundance, diversity, and integrity of Late Pleistocene fossils from Hoyo Negro give us a unique opportunity to reconstruct animal and plant life on the Yucatán Peninsula at the end of the last Ice Age,” said Rissolo.

    In November 2019, a group of researchers including Rissolo and a cave diving team led by Alberto Nava set out to recover the giant ground sloth’s pelvis through a meticulously planned expedition. Rising sea levels had flooded the cave system at the end of the last Ice Age, making the pelvis’ retrieval impossible for all but the most experienced divers. Over the course of the expedition, the team would have to work across international lines and unite talents in paleontology, 3D-modeling, engineering and virtual reality to safely bring this fragment of history back to light.

    New discovery (and a challenge) for science

    Cave divers discovered the giant ground sloth’s remains during initial dives into Hoyo Negro in 2007. Under the direction of Mexico’s National Institute of Anthropology and History (INAH) and the expert guidance of James Chatters and Blaine Schubert, paleontologists specializing in late-Ice Age species, divers removed all of the sloth’s bones save for a few vertebrae, an arm and its pelvis. With the bones in hand, researchers made a marvelous discovery: the sloth was a member of an entirely new species.

    “For a new species, it’s pretty good to have that much [of the skeleton],” said Chatters. “The preservation is absolutely incredible.”

    Scientists named the giant ground sloth Nohochichak xibalbahkah, Mayan for “The great claw that dwells in the underworld.” Alive, it would have stood at six to seven feet on its hind legs and weighed an estimated 2,000 pounds. Its pelvis was the last major bone missing from its skeleton and a key component in reconstructing its likeness.

    Rissolo and colleagues began preparing for the effort to retrieve the pelvis a full year in advance. Using QI’s high-resolution, walk-in virtual reality facility, the SunCAVE, they planned the divers’ route through the cave system and into Hoyo Negro. From the diving platform, the divers would descend in almost complete darkness into a narrow corridor and travel 200 feet to the edge of the black pit. The pelvis lay 90 feet below, upside down and darkened with age.

    The bone’s remarkable size posed an additional challenge. The team would have to design a support frame that was sturdy enough to protect its cargo, but not so bulky that it would scrape against the tunnel walls. Using images captured during a previous dive, Chatters and engineers at the QI Prototyping Lab, QI Drone Lab and East Tennessee State University recreated the pelvis as a 3D, digital model that they could rotate and study in close detail. Now, they could identify weak spots in the bone and design a frame that would cradle each part of the pelvis.

    The design seemed to be coming along. The bulk of the team had already set out for the Yucatán to prepare the camp site and look after logistics. All that remained was for the engineering team back home to finish their design, 3D-print the frame and send it on its way.

    Then, days before the dive, researchers had to abandon their plan. The frame they’d drafted was too expensive to produce, and its dimensions made it impossible for their 3D printer to process.

    In a burst of inspiration, Brett Butler, an engineer with the QI Prototyping Lab, turned to a local surfboard shaper with a background in industry. The engineering team needed a material that would be easy to maneuver underwater and fiberglass, a material used to build surfboards, fit the description. Butler told the surfboard shaper what he had in mind.

    “Of course, he thought I was crazy,” said Butler. “Who would call someone and ask them to help build a custom cradle for a 40,000-year-old giant ground sloth pelvis within a week?”

    Luckily, the surfboard shaper agreed. As he crafted a cradle for the sloth’s pelvis out of fiberglass, Butler and the other engineers created supporting materials that would protect the pelvis as it was lifted by divers from its depth of 140 feet below sea level, hoisted 30 feet up and out of the cave entrance, and driven over jungle roads.

    They finished just in time. On November 11, 2019, Butler flew to Mexico to deliver the pelvis’s cradle to the team waiting in the jungles of the Yucatán. Soon afterward, Rissolo, Butler and their colleagues settled in to watch as divers strapped on layers of dive gear, checked their closed circuit rebreathers, and ferried their invention into the cave.

    History, reassembled

    The team waited four hours for the divers to return. Emotions during the wait were mixed; Chatters, who had eight years of experience extracting fossils from Hoyo Negro, said he felt confident that the divers had a reliable routine. Others were less sanguine.

    When the divers reappeared below the diving platform for a safety stop, pelvis in tow, the entire camp celebrated. Team members took turns lying on the platform with their faces in the water, peering through a dive mask at the fossil they had dreamed of for months.

    “The giant ground sloth pelvis is the biggest fossil ever recovered from Hoyo Negro and the underwater portion of the recovery went exactly as planned and rehearsed. It was a fantastic way to end a long day in the jungle,” said Butler.

    For thousands of years, the fossilized pelvis lay submerged, upside down, on the floor of Hoyo Negro, the “Black Hole.” Here, cave divers attach an engineered framework to the pelvis to lift it from the cave floor. Photo Credit: Mike Madden and Sam Meacham, CINDAQ

    The team used their engineered cradle to connect the pelvis to a line-and-pulley system and hoisted it 30 feet from the diving platform through the mouth of the cave. A final cheer heralded the fossil’s return to the world aboveground, and a success for the partnership between paleontology and engineering.

    After weathering thousands of years underwater, the pelvis now rests within Mexico’s National Museum of Anthropology. The information gleaned from the fossil will contribute to INAH’s larger mission of documenting, studying and preserving Mexico’s paleontological history. Roberto Junco Sanchez, Subdirector of Underwater Archaeology with INAH, says that the next step will be to share the results with others for future research.

    “It’s a unique opportunity to study new species, a heaven in terms of the Pleistocene fauna that roamed the Yucatán,” said Junco Sanchez.

    The effort to recover the pelvis of Nohochichak xibalbahkah was a highly collaborative process that drew on partnerships with many individuals and organizations. In addition to those named in the text, CHEI would like to thank Helena Barba Meinecke, Director of the Hoyo Negro Project; Brian Strauss; divers Roberto Chavez and Alex Alvarez; Christian McDonald of the Scripps Institution of Oceanography, professional photographer and videographer Mike Madden; scientific diver Sam Meacham of El Centro Investigador del Sistema Acuífero de Quintana Roo; Vid Petrovic, computer scientist and software engineer at QI; David Zollinger, engineer at East Tennessee State University; and Jeffrey Sandubrae and Falko Kuester at QI.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of California, San Diego (also referred to as UC San Diego or UCSD), is a public research university located in the La Jolla area of San Diego, California, in the United States.[12] The university occupies 2,141 acres (866 ha) near the coast of the Pacific Ocean with the main campus resting on approximately 1,152 acres (466 ha).[13] Established in 1960 near the pre-existing Scripps Institution of Oceanography, UC San Diego is the seventh oldest of the 10 University of California campuses and offers over 200 undergraduate and graduate degree programs, enrolling about 22,700 undergraduate and 6,300 graduate students. UC San Diego is one of America’s Public Ivy universities, which recognizes top public research universities in the United States. UC San Diego was ranked 8th among public universities and 37th among all universities in the United States, and rated the 18th Top World University by U.S. News & World Report ‘s 2015 rankings.

  • richardmitnick 1:39 pm on November 27, 2019 Permalink | Reply
    Tags: "World’s oldest comma shrimp was way ahead of the curve", , Eobodotria muisca "comma" shrimp, Paleontology, Scientists have discovered the world’s oldest “comma” shrimp a tiny crustacean shaped like its punctuation namesake.,   

    From Yale University: “World’s oldest comma shrimp was way ahead of the curve” 

    Yale University bloc

    From Yale University

    November 26, 2019
    Jim Shelton

    Eobodotria muisca (Photo credit: Javier Luque)

    Scientists have discovered the world’s oldest “comma” shrimp, a tiny crustacean shaped like its punctuation namesake.

    The 90-million-year-old creature fills in a major evolutionary gap for a family of marine animals now found in abundance around the planet, according to researchers from Yale and the University of Alaska. The discovery appears in the journal Proceedings of the Royal Society B on Nov. 27.

    The fossilized shrimp, named Eobodotria muisca, comes from Mesozoic rocks in tropical South America. Researchers found exceptionally well-preserved fossils representing more than 500 individuals between 6 and 8 millimeters long, with features that are rarely preserved in fossil crustaceans: mouthparts, the gut, tiny hairs, and small compound eyes.

    “We are amazed by how similar Eobodotria muisca is to today’s species,” said Yale paleontologist Javier Luque, lead author of the study. “There are eight families or main groups of living comma shrimp, and none of them have a confirmed fossil occurrence. This means we had no idea when modern comma shrimp evolved, until now.”

    The only previous record of a modern-looking comma shrimp is a 160-million-year-old fossil from Europe, Luque said. Although that shrimp fit within the range of comma shrimp body forms, it couldn’t be linked to any of the main modern families of comma shrimp.

    Eobodotria muisca, on the other hand, belongs to the Bodotriidae family of living comma shrimp, Luque said, extending the fossil record of that family of shrimp by nearly 100 million years.

    The new species lived during the mid-Cretaceous period, when a long, narrow inland sea covered a large part of what is today the Eastern and Central Andes of Colombia. Luque found the fossils together with fossils of the crab Callichimaera perplexa. Eobodotria muisca is named after the Muisca native Americans who lived in the Colombian Andes.

    Luque said that the similarity between Eobodotria muisca and its modern relatives suggests that the rates of external anatomical changes over millions of years in this group was low compared to other crustacean groups found in the same location. He also noted that the new cache of fossils is the first of its kind in northern South America.

    Sarah Gerken of the University of Alaska-Anchorage is co-author of the study.

    Gerken and Luque said most of the Eobodotria muisca fossils they found were adult males. Large aggregations of males usually happen in the water column when they are searching for females by means of their large antennae for smelling and their flappy tail appendages for swimming — both features that females lack, the researchers explained.

    One possible explanation for this unusual accumulation of adult males is that they could have died suddenly in the water column while swarming in search of females, and then sunk down to the soft bottom where they fossilized, Gerken and Luque said.

    The researchers said the discovery not only helps paleontologists understand the origin of the comma shrimp’s curved body, it also can be used to help understand the origins of related crustaceans on the evolutionary family tree.

    View a live 3D model of Eobodotria muisca in the video below:

    Prehistoric Shrimp Eobodotria Muisca

    See the full article here .


    Please help promote STEM in your local schools.

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    Yale University Campus

    Yale University comprises three major academic components: Yale College (the undergraduate program), the Graduate School of Arts and Sciences, and the professional schools. In addition, Yale encompasses a wide array of centers and programs, libraries, museums, and administrative support offices. Approximately 11,250 students attend Yale.

  • richardmitnick 1:47 pm on November 6, 2019 Permalink | Reply
    Tags: "Exceptional Fossils May Need a Breath of Air to Form", , , Jackson School of Geosciences, , Paleontology, , The best-preserved fossil deposits are called “Konservat-lagerstätten.”,   

    From University of Texas at Austin – Jackson School of Geosciences: “Exceptional Fossils May Need a Breath of Air to Form” 

    U Texas Austin bloc

    From University of Texas at Austin – Jackson School of Geosciences

    November 5, 2019

    A fossilized mantle of a vampyropod, a relative tothe vampire squid. The ink sacis the raised structure in the center, and muscles have a striated appearance. Credit: Rowan Martindale/The University of Texas at Austin Jackson School of Geosciences.

    Some of the world’s most exquisite fossil beds were formed millions of years ago during time periods when the Earth’s oceans were largely without oxygen.

    That association has led paleontologists to believe that the world’s best-preserved fossil collections come from choked oceans. But research led by The University of Texas at Austin has found that while low oxygen environments set the stage, it takes a breath of air to catalyze the fossilization process.

    “The traditional thinking about these exceptionally preserved fossil sites is wrong,” said lead author Drew Muscente. “It is not the absence of oxygen that allows them to be preserved and fossilized. It is the presence of oxygen under the right circumstances.”

    The research was published in the journal PALAIOS on November 5.

    Muscente conducted the research during a postdoctoral research fellowship at the UT Jackson School of Geosciences. He is currently an assistant professor at Cornell College in Mount Vernon, Iowa. The research co-authors are Jackson School Assistant Professor Rowan Martindale, Jackson School undergraduate students Brooke Bogan and Abby Creighton and University of Missouri Associate Professor James Schiffbauer.

    The best-preserved fossil deposits are called “Konservat-lagerstätten.” They are rare and scientifically valuable because they preserve soft tissues along with hard ones – which in turn, preserves a greater variety of life from ancient ecosystems.

    “When you look at lagerstätten, what’s so interesting about them is everybody is there,” said Bogan. “You get a more complete picture of the animal and the environment, and those living in it.”

    The research examined the fossilization history of an exceptional fossil site located at Ya Ha Tinda Ranch in Canada’s Banff National Park. The site, which Martindale described in a 2017 paper [Geology], is known for its cache of delicate marine specimens from the Early Jurassic – such as lobsters and vampire squids with their ink sacks still intact—preserved in slabs of black shale.

    During the time of fossilization, about 183 million years ago, high global temperatures sapped oxygen from the oceans. To determine if the fossils did indeed form in an oxygen-deprived environment, the team analyzed minerals in the fossils. Since different minerals form under different chemical conditions, the research could determine if oxygen was present or not.

    “The cool thing about this work is that we can now understand the modes of formation of these different minerals as this organism fossilizes,” Martindale said. “A particular pathway can tell you about the oxygen conditions.”

    The analysis involved using a scanning electron microscope to detect the mineral makeup.

    “You pick points of interest that you think might tell you something about the composition,” said Creighton, who analyzed a number of specimens. “From there you can correlate to the specific minerals.”

    The workup revealed that the vast majority of the fossils are made of apatite – a phosphate-based mineral that needs oxygen to form. However, the research also found that the climatic conditions of a low-oxygen environment helped set the stage for fossilization once oxygen became available.

    That’s because periods of low ocean oxygen are linked to high global temperatures that raise sea levels and erode rock, which is a rich source of phosphate to help form fossils. If the low oxygen environment persisted, this sediment would simply release its phosphate into the ocean. But with oxygen around, the phosphate stays in the sediment where it could start the fossilization process.

    Muscente said that the apatite fossils of Ya Ha Tinda point to this mechanism.

    A fossilized lobster claw that may come from a new species. Rowan Martindale, the University of Texas at Austin.

    The research team does not know the source of the oxygen. But Muscente wasn’t surprised to find evidence for it because the organisms that were fossilized would have needed to breathe oxygen when they were alive.

    The researchers plan to continue their work by analyzing specimens from exceptional fossil sites in Germany and the United Kingdom that were preserved around the same time as the Ya Ha Tinda specimens and compare their fossilization histories.

    The research was funded by the National Science Foundation and the Jackson School of Geosciences.

    See the full article here .


    Please help promote STEM in your local schools.

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    U Texas at Austin

    U Texas Austin campus

    In 1839, the Congress of the Republic of Texas ordered that a site be set aside to meet the state’s higher education needs. After a series of delays over the next several decades, the state legislature reinvigorated the project in 1876, calling for the establishment of a “university of the first class.” Austin was selected as the site for the new university in 1881, and construction began on the original Main Building in November 1882. Less than one year later, on Sept. 15, 1883,

  • richardmitnick 11:09 am on September 8, 2019 Permalink | Reply
    Tags: Animals first form nanoparticles of amorphous calcium carbonate., Paleontology,   

    From UC Santa Barbara: “Unusual Building Blocks” 

    UC Santa Barbara Name bloc
    From UC Santa Barbara

    September 4, 2019
    Harrison Tasoff

    The calcium carbonate shells of ancient animals like this ammonite often remain intact after fossilization.

    The animal kingdom abounds with creatures that grow hard shells, carapaces and skeletons. But complex life was pretty squishy when it first evolved, so when and how did this change?

    UC Santa Barbara paleontologist Susannah Porter and her colleagues tackled this question and found that when carbonate skeletons were first evolving more than 500 million years ago, diverse groups of animals all converged on a similar, counterintuitive process for biomineralization.

    The researchers’ findings appear in a new paper published in the Proceedings of the National Academy of Sciences.

    Today many unrelated animals build their skeletons or shells out of calcium carbonate — including echinoderms, mollusks and corals. Instead of building crystals ion-by-ion from the surrounding sea water, these animals use amorphous, or non-crystalline, nanoparticles as their building blocks of choice.

    “In fact, crystallization by particle attachment actually seems to be the prevailing method of biomineralization as far as we can tell,” said Porter, a professor of earth science.

    Rather than building their skeletons at a molecular level, these animals first form nanoparticles of amorphous calcium carbonate. They then store these particles in vesicles that can be used to transport them to the site of crystallization.

    This method of crystallization was first documented more than 20 years ago in the teeth of sea urchins. Since then, scientists have noticed the process throughout the animal kingdom, and involving different minerals. What’s more, the different groups of animals seem to have independently settled on this method of biomineralization, so it must have something going for it.

    Given its ubiquity, Porter and her collaborators wanted to determine how far back they could find evidence of this process. “We obviously can’t watch these Cambrian and Ediacaran organisms make their skeletons, so we need to have a proxy,” she said. Porter’s colleague, first author Pupa Gilbert, of the University of Wisconsin-Madison, had previously found that crystallization by particle attachment leaves an irregular particulate texture in the shells and skeletons when they’re viewed under a scanning electron microscope.

    Custom-designed scanning transmission electron microscope at Cornell University by David Muller/Cornell University

    A cretaceous ammonite displays the grainy texture of crystallization by particle attachment when viewed under a scanning electron microscope.
    Photo Credit: SUSANNAH PORTER

    The team saw this same telltale pattern upon imaging fossils more than 500 million years old. In fact, this signature was preserved even in material that had subsequently converted into another mineral.

    “It’s spectacular,” Porter exclaimed, “the fact that we can see this detail at the sub-micrometer level.”

    Among the ancient material Porter and her collaborators examined were fossils of Cloudina, a genus that includes some of the earliest animals that formed a mineralized skeleton. The genus was named after UC Santa Barbara’s own Preston Cloud, the late professor of biogeology, and preeminent researcher in the study of early life.

    The team saw the same irregular nanoparticulate texture in Cloudina fossils as in other animals that form crystals by particle attachment. “This shows that, even when animals were first evolving mineralized skeletons, and were maybe not so good at biomineralizing, they were already choosing this mechanism,” Porter said.

    The researchers’ findings suggest that, even early on, there was selection for this particular mechanism across different lineages. “When you see something that is selected for over and over again, it suggests that it is the most advantageous one,” Porter said.

    Although it’s counterintuitive that animals would use amorphous material to create the crystals that ultimately form their skeletons or shells, Porter explained that this mechanism seems to permit greater control over mineralization than simply building ion by ion, as the traditional models suggested.

    For one, these particles are incredibly stable when confined in vesicles: The material doesn’t immediately crystallize but remains amorphous. This allows the animal to keep ingredients around and available yet maintain flexibility regarding when and where the mineralized skeleton forms.

    Additionally, compounds like calcium carbonate can take different structures — thereby forming different minerals — depending on environmental conditions. By storing the molecules in an amorphous state, the animal can better control what form, or polymorph, they become, Porter explained.

    “It’s like having some frozen cookie dough around that you’re later going to bake into cookies,” she said.

    Porter is interested in the large-scale patterns of when lineages first evolved skeletons and how those skeletons were affected by the environmental and ecological conditions of the time. She recently submitted a paper looking at how the patterns of carbonate biomineralizers shifted between the Ediacaran and Cambrian periods, when complex animals began to appear in the fossil record.

    She suspects that the earliest biomineralizers, like Cloudina, didn’t have particularly strong control over the process of building their skeletons. “But by the time you get to the Cambrian, the carbonate mineralizers have shells that are complex and organized,” said Porter. “They have much greater control over their skeletons.”

    See the full article here .


    Please help promote STEM in your local schools.

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    UC Santa Barbara Seal
    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

  • richardmitnick 9:19 am on April 9, 2019 Permalink | Reply
    Tags: Children’s Museum of Indianapolis, Mission Jurassic, Paleontology, ,   

    From SLAC National Accelerator Lab: “A mile-long graveyard of Jurassic fossils sparks a new international science collaboration” 

    From SLAC National Accelerator Lab

    March 28, 2019
    Ali Sundermier

    Kimberly Calkins and Dallas Evans, lead curator of natural science and paleontology, with a sauropod femur at the upper sauropod quarry of The Jurassic Mile dig site. (Children’s Museum of Indianapolis)

    The Children’s Museum of Indianapolis announced plans this week for Mission Jurassic, a project that will support paleontological excavation of a fossil-rich plot of land in northern Wyoming. The project will bring together scientists from around the world, including the Department of Energy’s SLAC National Accelerator Laboratory, to reveal dramatic new secrets about the world of millions of years ago.

    “Mission Jurassic is a wonderful project because it’s not just an isolated fossil – it’s a suite of different organisms, including dinosaurs and plants, in a single location,” says SLAC scientist Nick Edwards. “We hope that through our involvement in this project, we will contribute some new information to the preservation, chemistry and maybe even the basic understanding of these extinct organisms, ancient ecosystems, and Earth history on the broader scale.”

    The Children’s Museum will serve as the Mission Jurassic leader. The project is made possible through a lead gift from Lilly Endowment Inc. Spearheaded by Phil Manning and Victoria Egerton of the University of Manchester in England, both scientists-in-residence at The Children’s Museum, more than 100 scientists from three countries will join forces to investigate the rare confluence of Jurassic Period fossils, trackways and fossilized plants. The site will provide clues that promise to tell a more complete story about the Jurassic Period.

    “We have been using SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) for over a decade to help map the subtle changes in chemistry that are a function of burial environments,” Manning says.

    SLAC SSRL Campus

    SLAC SSRL PEP collider map


    “This work has real-world impact on how we might plan the long-term burial and disposal of waste in the 21st Century. We use the fossil record as a ‘hindsight laboratory’ that can better inform science on the mass transfer of compounds from the biosphere into the lithosphere”.

    The Jurassic Mile

    Project leaders are calling the fossil-rich, mile-square plot of land the Jurassic Mile. There are four main quarries within the multi-level, 640-acre site that offer a diverse assemblage of Morrison Formation articulated and semi-articulated dinosaurs. It has also yielded associated animals, fossil plants and dinosaur trackways of the Late Jurassic Period, 150 million years ago.

    Nearly 600 specimens weighing more than six tons have been collected from this site over the past two years, despite the fact that only a fraction of the site has been explored. They include the bones of an 80-foot-long sauropod (Brachiosaur) and 90-foot-long Diplodocid. A 6-foot-6-inch sauropod scapula (shoulder bone) and several blocks containing articulated bones are among the material collected during the 2018 field season. A 5-foot-1-inch femur was revealed at the announcement on March 25, 2019.

    Probing our world at the atomic level

    SLAC, a key partner working with the University of Manchester team, will shine bright X-rays onto the fossils at the SSRL, a DOE Office of Science user facility that produces X-ray beams perfectly tailored for probing the world at the atomic and molecular level. New imaging techniques being developed by the team have already resulted in multiple high-impact scientific publications.

    “Our primary instrument at SSRL is unique because it can do elemental imaging, which tells us where the elements are in fossils, and it can also do absorption spectroscopy, which tells us what chemical state they’re in,” says Uwe Bergmann, a distinguished staff scientist at SLAC. “It allows us to detect a wide range of important biological and geochemical elements, from light elements like phosphorous and sulfur all the way to the transition metals.”

    Specimens from the well-preserved fossil remains at the Jurassic Mile site will form the basis for a major expansion of The Children’s Museum of Indianapolis’ permanent Dinosphere exhibit that will add creatures from the Jurassic Period. The project is already utilizing cutting-edge science, from particle accelerators to some of the most powerful computers on the planet, to help resurrect the Jurassic dinosaurs and add momentum to the process of unearthing the lost world and forgotten lives.

    This article is based on a press release from The Children’s Museum of Indianapolis.

    From the press release, no image credits:


    See the full article here .

    Please help promote STEM in your local schools.

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    SLAC/LCLS II projected view

    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

  • richardmitnick 10:52 am on April 1, 2019 Permalink | Reply
    Tags: "Annals of the Former World-The Day the Dinosaurs Died", , Cretaceous period, , Paleogene period, Paleontologist Robert DePalma, Paleontology, The colossal “Deccan” volcanic eruptions, The Hell Creek Formation, The KT boundary marks the dividing line between the Cretaceous period and the Tertiary period., The KT layer was laced with the rare metal iridium which they hypothesized was from the dusty remains of an asteroid impact-so geologist Walter Alvarez and his father Luis Alvarez, , The Tertiary has been redefined as the Paleogene,   

    From The New Yorker via U Washington: “Annals of the Former World-The Day the Dinosaurs Died” 

    U Washington

    University of Washington

    Rea Irvin

    From The New Yorker

    April 8, 2019
    Douglas Preston

    A field assistant, Rudy Pascucci, left, and the paleontologist Robert DePalma, right, at DePalma’s dig site. Of his discovery, DePalma said, “It’s like finding the Holy Grail clutched in the bony fingers of Jimmy Hoffa, sitting on top of the Lost Ark.”

    If, on a certain evening about sixty-­six million years ago, you had stood somewhere in North America and looked up at the sky, you would have soon made out what appeared to be a star. If you watched for an hour or two, the star would have seemed to grow in brightness, although it barely moved. That’s because it was not a star but an asteroid, and it was headed directly for Earth at about forty-five thousand miles an hour. Sixty hours later, the asteroid hit. The air in front was compressed and violently heated, and it blasted a hole through the atmosphere, generating a supersonic shock wave. The asteroid struck a shallow sea where the Yucatán peninsula is today. In that moment, the Cretaceous period ended and the Paleogene period began.

    A few years ago, scientists at Los Alamos National Laboratory used what was then one of the world’s most powerful computers, the so-called Q Machine, to model the effects of the impact.

    The ASCI Q machine at LANL.

    The result was a slow-motion, second-by-second false-color video of the event. Within two minutes of slamming into Earth, the asteroid, which was at least six miles wide, had gouged a crater about eighteen miles deep and lofted twenty-five trillion metric tons of debris into the atmosphere. Picture the splash of a pebble falling into pond water, but on a planetary scale. When Earth’s crust rebounded, a peak higher than Mt. Everest briefly rose up. The energy released was more than that of a billion Hiroshima bombs, but the blast looked nothing like a nuclear explosion, with its signature mushroom cloud. Instead, the initial blowout formed a “rooster tail,” a gigantic jet of molten material, which exited the atmosphere, some of it fanning out over North America. Much of the material was several times hotter than the surface of the sun, and it set fire to everything within a thousand miles. In addition, an inverted cone of liquefied, superheated rock rose, spread outward as countless red-hot blobs of glass, called tektites, and blanketed the Western Hemisphere.

    Some of the ejecta escaped Earth’s gravitational pull and went into irregular orbits around the sun. Over millions of years, bits of it found their way to other planets and moons in the solar system. Mars was eventually strewn with the debris—just as pieces of Mars, knocked aloft by ancient asteroid impacts, have been found on Earth. A 2013 study in the journal Astrobiology estimated that tens of thousands of pounds of impact rubble may have landed on Titan, a moon of Saturn, and on Europa and Callisto, which orbit Jupiter—three satellites that scientists believe may have promising habitats for life. Mathematical models indicate that at least some of this vagabond debris still harbored living microbes. The asteroid may have sown life throughout the solar system, even as it ravaged life on Earth.

    The asteroid was vaporized on impact. Its substance, mingling with vaporized Earth rock, formed a fiery plume, which reached halfway to the moon before collapsing in a pillar of incandescent dust. Computer models suggest that the atmosphere within fifteen hundred miles of ground zero became red hot from the debris storm, triggering gigantic forest fires. As the Earth rotated, the airborne material converged at the opposite side of the planet, where it fell and set fire to the entire Indian subcontinent. Measurements of the layer of ash and soot that eventually coated the Earth indicate that fires consumed about seventy per cent of the world’s forests. Meanwhile, giant tsunamis resulting from the impact churned across the Gulf of Mexico, tearing up coastlines, sometimes peeling up hundreds of feet of rock, pushing debris inland and then sucking it back out into deep water, leaving jumbled deposits that oilmen sometimes encounter in the course of deep-sea drilling.

    The damage had only begun. Scientists still debate many of the details, which are derived from the computer models, and from field studies of the debris layer, knowledge of extinction rates, fossils and microfossils, and many other clues. But the over-all view is consistently grim. The dust and soot from the impact and the conflagrations prevented all sunlight from reaching the planet’s surface for months. Photosynthesis all but stopped, killing most of the plant life, extinguishing the phytoplankton in the oceans, and causing the amount of oxygen in the atmosphere to plummet. After the fires died down, Earth plunged into a period of cold, perhaps even a deep freeze. Earth’s two essential food chains, in the sea and on land, collapsed. About seventy-five per cent of all species went extinct. More than 99.9999 per cent of all living organisms on Earth died, and the carbon cycle came to a halt.

    Earth itself became toxic. When the asteroid struck, it vaporized layers of limestone, releasing into the atmosphere a trillion tons of carbon dioxide, ten billion tons of methane, and a billion tons of carbon monoxide; all three are powerful greenhouse gases. The impact also vaporized anhydrite rock, which blasted ten trillion tons of sulfur compounds aloft. The sulfur combined with water to form sulfuric acid, which then fell as an acid rain that may have been potent enough to strip the leaves from any surviving plants and to leach the nutrients from the soil.

    Today, the layer of debris, ash, and soot deposited by the asteroid strike is preserved in the Earth’s sediment as a stripe of black about the thickness of a notebook. This is called the KT boundary, because it marks the dividing line between the Cretaceous period and the Tertiary period. (The Tertiary has been redefined as the Paleogene, but the term “KT” persists.) Mysteries abound above and below the KT layer. In the late Cretaceous, widespread volcanoes spewed vast quantities of gas and dust into the atmosphere, and the air contained far higher levels of carbon dioxide than the air that we breathe now. The climate was tropical, and the planet was perhaps entirely free of ice. Yet scientists know very little about the animals and plants that were living at the time, and as a result they have been searching for fossil deposits as close to the KT boundary as possible.

    One of the central mysteries of paleontology is the so-called “three-­metre problem.” In a century and a half of assiduous searching, almost no dinosaur remains have been found in the layers three metres, or about nine feet, below the KT boundary, a depth representing many thousands of years. Consequently, numerous paleontologists have argued that the dinosaurs were on the way to extinction long before the asteroid struck, owing perhaps to the volcanic eruptions and climate change. Other scientists have countered that the three-metre problem merely reflects how hard it is to find fossils. Sooner or later, they’ve contended, a scientist will discover dinosaurs much closer to the moment of destruction.

    Locked in the KT boundary are the answers to our questions about one of the most significant events in the history of life on the planet. If one looks at the Earth as a kind of living organism, as many biologists do, you could say that it was shot by a bullet and almost died. Deciphering what happened on the day of destruction is crucial not only to solving the three-­metre problem but also to explaining our own genesis as a species.

    On August 5, 2013, I received an e-mail from a graduate student named Robert DePalma. I had never met DePalma, but we had corresponded on paleontological matters for years, ever since he had read a novel I’d written that centered on the discovery of a fossilized Tyrannosaurus rex killed by the KT impact. “I have made an incredible and unprecedented discovery,” he wrote me, from a truck stop in Bowman, North Dakota. “It is extremely confidential and only three others know of it at the moment, all of them close colleagues.” He went on, “It is far more unique and far rarer than any simple dinosaur discovery. I would prefer not outlining the details via e-mail, if possible.” He gave me his cell-phone number and a time to call.

    I called, and he told me that he had discovered a site like the one I’d imagined in my novel, which contained, among other things, direct victims of the catastrophe. At first, I was skeptical. DePalma was a scientific nobody, a Ph.D. candidate at the University of Kansas, and he said that he had found the site with no institutional backing and no collaborators. I thought that he was likely exaggerating, or that he might even be crazy. (Paleontology has more than its share of unusual people.) But I was intrigued enough to get on a plane to North Dakota to see for myself.

    DePalma’s find was in the Hell Creek geological formation, which outcrops in parts of North Dakota, South Dakota, Montana, and Wyoming, and contains some of the most storied dinosaur beds in the world.

    Hell Creek Formation near Ft. Peck Reservoir, Montana. Anky-man.

    At the time of the impact, the Hell Creek landscape consisted of steamy, subtropical lowlands and floodplains along the shores of an inland sea. The land teemed with life and the conditions were excellent for fossilization, with seasonal floods and meandering rivers that rapidly buried dead animals and plants.

    Dinosaur hunters first discovered these rich fossil beds in the late nineteenth century. In 1902, Barnum Brown, a flamboyant dinosaur hunter who worked at the American Museum of Natural History, in New York, found the first Tyrannosaurus rex here, causing a worldwide sensation. One paleontologist estimated that in the Cretaceous period Hell Creek was so thick with T. rexes that they were like hyenas on the Serengeti. It was also home to triceratops and duckbills.

    DePalma’s thesis adviser estimated that the site will keep specialists busy for half a century. “Robert’s got so much stuff that’s unheard of,” he said. “It will be in the textbooks.”
    Photograph by Richard Barnes for The New Yorker.

    The Hell Creek Formation spanned the Cretaceous and the Paleogene periods, and paleontologists had known for at least half a century that an extinction had occurred then, because dinosaurs were found below, but never above, the KT layer. This was true not only in Hell Creek but all over the world. For many years, scientists believed that the KT extinction was no great mystery: over millions of years, volcanism, climate change, and other events gradually killed off many forms of life. But, in the late nineteen-seventies, a young geologist named Walter Alvarez and his father, Luis Alvarez, a nuclear physicist, discovered that the KT layer was laced with unusually high amounts of the rare metal iridium, which, they hypothesized, was from the dusty remains of an asteroid impact. In an article in Science, published in 1980, they proposed that this impact was so large that it triggered the mass extinction, and that the KT layer was the debris from that event. Most paleontologists rejected the idea that a sudden, random encounter with space junk had drastically altered the evolution of life on Earth. But as the years passed the evidence mounted, until, in a 1991 paper, the smoking gun was announced: the discovery of an impact crater buried under thousands of feet of sediment in the Yucatán peninsula, of exactly the right age, and of the right size and geochemistry, to have caused a worldwide cataclysm. The crater and the asteroid were named Chicxulub, after a small Mayan town near the epicenter.

    One of the authors of the 1991 paper, David Kring, was so frightened by what he learned of the impact’s destructive nature that he became a leading voice in calling for a system to identify and neutralize threatening asteroids. “There’s no uncertainty to this statement: the Earth will be hit by a Chicxulub-size asteroid again, unless we deflect it,” he told me. “Even a three-hundred-metre rock would end world agriculture.”

    In 2010, forty-one researchers in many scientific disciplines announced, in a landmark Science article, that the issue should be considered settled: a huge asteroid impact caused the extinction. But opposition to the idea remains passionate. The main competing hypothesis is that the colossal “Deccan” volcanic eruptions, in what would become India, spewed enough sulfur and carbon dioxide into the atmosphere to cause a climatic shift. The eruptions, which began before the KT impact and continued after it, were among the biggest in Earth’s history, lasting hundreds of thousands of years, and burying half a million square miles of the Earth’s surface a mile deep in lava. The three-­metre gap below the KT layer, proponents argued, was evidence that the mass extinction was well under way by the time of the asteroid strike.

    In 2004, DePalma, at the time a twenty-­two-year-old paleontology undergraduate, began excavating a small site in the Hell Creek Formation. The site had once been a pond, and the deposit consisted of very thin layers of sediment. Normally, one geological layer might represent thousands or millions of years. But DePalma was able to show that each layer in the deposit had been laid down in a single big rainstorm. “We could see when there were buds on the trees,” he told me. “We could see when the cypresses were dropping their needles in the fall. We could experience this in real time.” Peering at the layers was like flipping through a paleo-history book that chronicled decades of ecology in its silty pages. DePalma’s adviser, the late Larry Martin, urged him to find a similar site, but one that had layers closer to the KT boundary.

    Today, DePalma, now thirty-seven, is still working toward his Ph.D. He holds the unpaid position of curator of vertebrate paleontology at the Palm Beach Museum of Natural History, a nascent and struggling museum with no exhibition space. In 2012, while looking for a new pond deposit, he heard that a private collector had stumbled upon an unusual site on a cattle ranch near Bowman, North Dakota. (Much of the Hell Creek land is privately owned, and ranchers will sell digging rights to whoever will pay decent money, paleontologists and commercial fossil collectors alike.) The collector felt that the site, a three-foot-deep layer exposed at the surface, was a bust: it was packed with fish fossils, but they were so delicate that they crumbled into tiny flakes as soon as they met the air. The fish were encased in layers of damp, cracked mud and sand that had never solidified; it was so soft that it could be dug with a shovel or pulled apart by hand. In July, 2012, the collector showed DePalma the site and told him that he was welcome to it.

    “I was immediately very disappointed,” DePalma told me. He was hoping for a site like the one he’d excavated earlier: an ancient pond with fine-grained, fossil-bearing layers that spanned many seasons and years. Instead, everything had been deposited in a single flood. But as DePalma poked around he saw potential. The flood had entombed everything immediately, so specimens were exquisitely preserved. He found many complete fish, which are rare in the Hell Creek Formation, and he figured that he could remove them intact if he worked with painstaking care. He agreed to pay the rancher a certain amount for each season that he worked there. (The specifics of the arrangement, as is standard practice in paleontology, are a closely guarded secret. The site is now under exclusive long-term lease.)

    The following July, DePalma returned to do a preliminary excavation of the site. “Almost right away, I saw it was unusual,” he told me. He began shovelling off the layers of soil above where he’d found the fish. This “overburden” is typically material that was deposited long after the specimen lived; there’s little in it to interest a paleontologist, and it is usually discarded. But as soon as DePalma started digging he noticed grayish-white specks in the layers which looked like grains of sand but which, under a hand lens, proved to be tiny spheres and elongated ­droplets. “I think, Holy shit, these look like microtektites!” DePalma recalled. Micro­tektites are the blobs of glass that form when molten rock is blasted into the air by an asteroid impact and falls back to Earth in a solidifying drizzle. The site appeared to contain micro­tektites by the million.

    As DePalma carefully excavated the upper layers, he began uncovering an extraordinary array of fossils, exceedingly delicate but marvellously well preserved. “There’s amazing plant material in there, all interlaced and interlocked,” he recalled. “There are logjams of wood, fish pressed against cypress-­tree root bundles, tree trunks smeared with amber.” Most fossils end up being squashed flat by the pressure of the overlying stone, but here everything was three-dimensional, including the fish, having been encased in sediment all at once, which acted as a support. “You see skin, you see dorsal fins literally sticking straight up in the sediments, species new to science,” he said. As he dug, the momentousness of what he had come across slowly dawned on him. If the site was what he hoped, he had made the most important paleontological discovery of the new century.

    In a century and a half of assiduous searching, almost no dinosaur remains have been found in the layers three metres, or about nine feet, below the KT boundary, a depth representing many thousands of years. Photograph by Richard Barnes for The New Yorker.

    DePalma grew up in Boca Raton, Florida, and as a child he was fascinated by bones and the stories they contained. His father, Robert, Sr., practices endodontic surgery in nearby Delray Beach; his great-uncle Anthony, who died in 2005, at the age of a hundred, was a renowned orthopedic surgeon who wrote several standard textbooks on the subject. (Anthony’s son, Robert’s cousin, is the film director Brian De Palma.)

    “Between the ages of three and four, I made a visual connection with the gracefulness of individual bones and how they fit together as a system,” DePalma told me. “That really struck me. I went after whatever on the dinner table had bones in it.” His family ­buried their dead pets in one spot and put the burial markers in another, so that he wouldn’t dig up the corpses; he found them anyway. He froze dead lizards in ice-cube trays, which his mother would discover when she had friends over for iced tea. “I was never into sports,” he said. “They tried to get me to do that so I would get along with the other kids. But I was digging up the baseball field looking for bones.”

    DePalma’s great-uncle Anthony, who lived in Pompano Beach, took him under his wing. “I used to visit him every other weekend and show him my latest finds,” DePalma said. When he was four, someone at a museum in Texas gave him a fragment of dinosaur bone, which he took to his great-uncle. “He taught me that all those little knobs and rough patches and protrusions on a bone had names, and that the bone also had a name,” DePalma said. “I was captivated.” At six or seven, on trips to Central Florida with his family, he started finding his own fossilized bones from mammals dating back to the Ice Age. He found his first dinosaur bone when he was nine, in Colorado.

    In high school, during the summer and on weekends, DePalma collected fossils, made dinosaur models, and mounted skeletons for the Graves Museum of Archaeology and Natural History, in Dania Beach. He loaned the museum his childhood fossil collection for display, but in 2004 the museum went bankrupt and many of the specimens were carted off to a community college. DePalma had no paperwork to prove his ownership, and a court refused to return his fossils, which numbered in the hundreds. They were mostly locked away in storage, unavailable for public display and enjoyment.

    Dismayed by what he called the “wasteful mismanagement” of his collection, DePalma adopted some unusual collecting practices. Typically, paleontologists cede the curation and the care of their specimens to the institutions that hold them. But DePalma insists on contractual clauses that give him oversight of the management of his specimens. He never digs on public land, because of what he considers excessive government red tape. But, without federal support for his work, he must cover almost all the costs himself. His out-of-pocket expenses for working the Hell Creek site amount to tens of thousands of dollars. He helps defray the expenses by mounting fossils, doing reconstructions, and casting and selling replicas for museums, private collectors, and other clients. At times, his parents have chipped in. “I squeak by,” he said. “If it’s a ­tossup between getting more PaleoBond”—an expensive liquid glue used to hold fossils together—“or changing the air-conditioning filter, I’m getting the PaleoBond.” He is single, and shares a three-bedroom apartment with casts of various dinosaurs, including one of a Nanotyrannus. “It’s hard to have a life outside of my work,” he said.

    DePalma’s control of his research collection is controversial. Fossils are a big business; wealthy collectors pay hundreds of thousands of dollars, even millions, for a rare specimen. (In 1997, a T. rex nicknamed Sue was sold at a Sotheby’s auction, to the Field Museum of Natural History, in Chicago, for more than $8.3 million.) The American market is awash in fossils illegally smuggled out of China and Mongolia. But in the U.S. fossil collecting on private property is legal, as is the buying, selling, and exporting of fossils. Many scientists view this trade as a threat to paleontology and argue that important fossils belong in museums. “I’m not allowed to have a private collection of anything I’m studying,” one prominent curator told me. DePalma insists that he maintains “the best of both worlds” for his fossils. He has deposited portions of his collection at several nonprofit institutions, including the University of Kansas, the Palm Beach Museum of Natural History, and Florida Atlantic University; some specimens are temporarily housed in various analytical labs that are conducting tests on them—all overseen by him.

    In 2013, DePalma briefly made news with a paper he published in the Proceedings of the National Academy of Sciences. Four years earlier, in Hell Creek, he and a field assistant, Robert Feeney, found an odd, lumpy growth of fossilized bone that turned out to be two fused vertebrae from the tail of a hadrosaur, a duck-billed dinosaur from the Cretaceous period. DePalma thought that the bone might have grown around a foreign object and encased it. He took it to Lawrence Memorial Hospital, in Kansas, where a CT technician scanned it for free in the middle of the night, when the machine was idle. Inside the nodule was a broken tyrannosaur tooth; the hadrosaur had been bitten by a tyrannosaur and escaped.

    The discovery helped refute an old hypothesis, revived by the formidable paleontologist Jack Horner, that T. rex was solely a scavenger. Horner argued that T. rex was too slow and lumbering, its arms too puny and its eyesight too poor, to prey on other creatures. When DePalma’s find was picked up by the national media, Horner dismissed it as “speculation” and merely “one data point.” He suggested an alternative scenario: the T. rex might have accidentally bitten the tail of a sleeping hadrosaur, thinking that it was dead, and then “backed away” when it realized its mistake. “I thought that was absolutely preposterous,” DePalma told me. At the time, he told the Los Angeles Times, “A scavenger doesn’t come across a food source and realize all of a sudden that it’s alive.” Horner eventually conceded that T. rex may have hunted live prey. But, when I asked Horner about DePalma recently, he said at first that he didn’t remember him: “In the community, we don’t get to know students very well.”

    Without his Ph.D., DePalma remains mostly invisible, awaiting the stamp of approval that signals the beginning of a serious research career. Several paleontologists I talked to had not heard of him. Another, who asked not to be named, said, “Finding that kind of fossil was pretty cool, but not life-­changing. People sometimes think I’m dumb because I often say I don’t have the answers—we weren’t there when a fossil was formed. There are other people out there who say they do know, and he’s one of those people. I think he can overinterpret.”

    After receiving DePalma’s e-mail, I made arrangements to visit the Hell Creek site; three weeks later I was in Bowman. DePalma pulled up to my hotel in a Toyota 4Runner, its stereo blasting the theme to “Raiders of the Lost Ark.” He wore a coarse cotton work shirt, cargo pants with canvas ­suspenders, and a suède cowboy hat with the left brim snapped up. His face was tanned from long days in the sun and he had a five-day-old beard.

    I got in, and we drove for an hour or so, turning through a ranch gate and following a maze of bone-rattling roads that eventually petered out in a grassy basin. The scattered badlands of Hell Creek form an otherworldly landscape. This is far-flung ranching and farming country; prairies and sunflower fields stretch to the horizon, domed by the great blue skies of the American West. Roads connect small towns—truck stop, church, motel, houses and trailers—and lonely expanses roll by in between. Here and there in the countryside, abandoned farmhouses lean into the ground. Over millions of years, the Hell Creek layer has been heavily eroded, leaving only remnants, which jut from the prairie like so many rotten teeth. These lifeless buttes and pinnacles are striped in beige, chocolate, yellow, maroon, russet, gray, and white. Fossils, worked loose by wind and rain, spill down the sides.

    When we arrived, DePalma’s site lay open in front of us: a desolate hump of gray, cracked earth, about the size of two soccer fields. It looked as if a piece of the moon had dropped there. One side of the deposit was cut through by a sandy wash, or dry streambed; the other ended in a low escarpment. The dig was a three-foot-deep rectangular hole, sixty feet long by forty feet wide. A couple of two-by-fours, along with various digging tools and some metal pipe for taking core samples, leaned against the far side of the hole. As we strolled around the site, I noticed on DePalma’s belt a long fixed-blade knife and a sheathed bayonet—a Second World War relic that his uncle gave him when he was twelve, he said.

    He recalled the moment of discovery. The first fossil he removed, earlier that summer, was a five-foot-long freshwater paddlefish. Paddlefish still live today; they have a long bony snout, with which they probe murky water in search of food. When DePalma took out the fossil, he found underneath it a tooth from a mosasaur, a giant carnivorous marine reptile. He wondered how a freshwater fish and a marine reptile could have ended up in the same place, on a riverbank at least several miles inland from the nearest sea. (At the time, a shallow body of water, called the Western Interior Seaway, ran from the proto-­Gulf of Mexico up through part of North America.) The next day, he found a two-foot-wide tail from another marine fish; it looked as if it had been violently ripped from the fish’s body. “If the fish is dead for any length of time, those tails decay and fall apart,” DePalma said. But this one was perfectly intact, “so I knew that it was transported at the time of death or around then.” Like the mosasaur tooth, it had somehow ended up miles inland from the sea of its origin. “When I found that, I thought, There’s no way, this can’t be right,” DePalma said. The discoveries hinted at an extraordinary conclusion that he wasn’t quite ready to accept. “I was ninety-eight per cent con­vinced at that point,” he said.

    The following day, DePalma noticed a small disturbance preserved in the sediment. About three inches in diameter, it appeared to be a crater formed by an object that had fallen from the sky and plunked down in mud. Similar formations, caused by hailstones hitting a muddy surface, had been found before in the fossil record. As DePalma shaved back the layers to make a cross-­section of the crater, he found the thing itself—not a hailstone but a small white sphere—at the bottom of the crater. It was a tektite, about three millimetres in diameter—the fallout from an ancient asteroid impact. As he continued excavating, he found another crater with a tektite at the bottom, and another, and another. Glass turns to clay over millions of years, and these tektites were now clay, but some still had glassy cores. The microtektites he had found earlier might have been carried there by water, but these had been trapped where they fell—on what, DePalma believed, must have been the very day of the disaster.

    “When I saw that, I knew this wasn’t just any flood deposit,” DePalma said. “We weren’t just near the KT boundary—this whole site is the KT boundary!” From surveying and mapping the layers, DePalma hypothesized that a massive inland surge of water flooded a river valley and filled the low-lying area where we now stood, perhaps as a result of the KT-impact tsunami, which had roared across the proto-Gulf and up the Western Interior Seaway. As the water slowed and became slack, it deposited everything that had been caught up in its travels—the heaviest material first, up to whatever was floating on the surface. All of it was quickly entombed and preserved in the muck: dying and dead creatures, both marine and freshwater; plants, seeds, tree trunks, roots, cones, pine needles, flowers, and pollen; shells, bones, teeth, and eggs; tektites, shocked minerals, tiny diamonds, iridium-laden dust, ash, charcoal, and amber-smeared wood. As the sediments settled, blobs of glass rained into the mud, the largest first, then finer and finer bits, until grains sifted down like snow.

    “We have the whole KT event preserved in these sediments,” DePalma said. “With this deposit, we can chart what happened the day the Cretaceous died.” No paleontological site remotely like it had ever been found, and, if DePalma’s hypothesis proves correct, the scientific value of the site will be immense. When Walter Alvarez visited the dig last summer, he was astounded. “It is truly a magnificent site,” he wrote to me, adding that it’s “surely one of the best sites ever found for telling just what happened on the day of the impact.”

    When DePalma finished showing me the dig, he introduced me to a field assistant, Rudy Pascucci, the director of the Palm Beach Museum. Pascucci, a muscular man in his fifties, was sunburned and unshaven, and wore a sleeveless T-shirt, snakeproof camouflage boots, and a dusty Tilley hat. The two men gathered their tools, got down on the floor of the hole, and began probing the three-foot-high walls of the deposit.

    For rough digging, DePalma likes to use his bayonet and a handheld Marsh pick, popularized by the nineteenth-­century Yale paleontologist Othniel C. Marsh, who pioneered dinosaur-hunting in the American West and dis­covered eighty new species. The pick was given to him by David Burnham, his thesis adviser at Kansas, when he completed his master’s degree. For fine work, DePalma uses X-Acto knives and brushes—the typical tools of a paleontologist—as well as dental instruments given to him by his father.

    The deposit consisted of dozens of thin layers of mud and sand. Lower down, it graded into a more turbulent band of sand and gravel, which contained the heavier fish fossils, bones, and bigger tektites. Below that layer was a hard surface of sandstone, the original Cretaceous bedrock of the site, much of which had been scoured smooth by the flood.

    Paleontology is maddening work, its progress typically measured in millimetres. As I watched, DePalma and Pascucci lay on their stomachs under the beating sun, their eyes inches from the dirt wall, and picked away. DePalma poked the tip of an X-Acto into the thin laminations of sediment and loosened one dime-size flake at a time; he’d examine it closely, and, if he saw nothing, flick it away. When the chips accumulated, he gathered them into small piles with a paintbrush; when those piles accumulated, Pascucci swept them into larger piles with a broom and then shovelled them into a heap at the far end of the dig.

    Occasionally, DePalma came across small plant fossils—flower petals, leaves, seeds, pine needles, and bits of bark. Many of these were mere impressions in the mud, which would crack and peel as soon as they were exposed to the air. He quickly squirted them with PaleoBond, which soaked into the fossils and held them together. Or, us­ing another technique, he mixed a batch of plaster and poured it on the spec­imen before it fell apart. This would preserve, in plaster, a reverse image of the fossil; the original was too short-lived to be saved.

    When the mosquitoes got bad, DePalma took out a briar pipe and packed it with Royal Cherry Cavendish tobacco. He put a lighter to it and vigorously puffed, wreathing himself in sickly-­sweet smoke, then went back to work. “I’m like a shopaholic in a shoe store,” he said. “I want everything!”

    He showed me the impression of a round object about two inches wide. “This is either a flower or an echinoderm,” he said, referring to a group of marine life-forms that includes sea urchins and starfish. “I’ll figure it out in the lab.” He swiftly entombed it in Paleo­Bond and plaster. Next, he found a perfect leaf, and near that a seed from a pinecone. “Cretaceous mulch,” he said, dismissively; he already had many similar examples. He found three more small craters with tektites in them, which he sectioned and photographed. Then his X-Acto blade turned up a tiny brown bone—a jaw, less than a quarter inch in length. He held it up between his fingers and peered at it with a lens.

    “A mammal,” he said. “This one was already dead when it was buried.” Weeks later, in the lab, he identified the jaw as probably belonging to a mam­mal distantly related to primates—including us.

    In one fell swoop, DePalma may have filled in the gap in the fossil record. Photograph by Richard Barnes for The New Yorker.

    Half an hour later, DePalma discovered a large feather. “Every day is Christmas out here,” he said. He exposed the feather with precise movements. It was a crisp impression in the layer of mud, perhaps thirteen inches long. “This is my ninth feather,” he said. “The first fossil feathers ever found at Hell Creek. I’m convinced these are dinosaur feathers. I don’t know for sure. But these are primitive feathers, and most are a foot long. There are zero birds that big from Hell Creek with feathers this primitive. It’s more parsimonious to suggest it was a known dinosaur, most likely a theropod, possibly a raptor.” He kept digging. “Maybe we’ll find the raptor that these feathers came from, but I doubt it. These feathers could have floated from a long way off.”

    His X-Acto knife unearthed the edge of a fossilized fin. Another paddlefish came to light; it later proved to be nearly six feet long. DePalma probed the sediment around it, to gauge its position and how best to extract it. As more of it was exposed, we could clearly see that the fish’s two-foot-long snout had broken when it was forced—probably by the flood’s surge—against the branches of a submerged araucaria tree. He noted that every fish he’d found in the site had died with its mouth open, which may indicate that the fish had been gasping as they suffocated in the sediment-laden water.

    “Most died in a vertical position in the sediment, didn’t even tip over on their sides,” he said. “And they weren’t scavenged, because whatever would have dug them up afterward was probably gone.” He chipped away around the paddlefish, exposing a fin bone, then a half-dollar-size patch of fossilized skin with the scales perfectly visible. He treated these by saturating them with his own special blend of hardener. Because of the extreme fragility of the fossils, he would take them back to his lab, in Florida, totally encased in sediment, or “matrix.” In the lab, he would free each fossil under a magnifying glass, in precisely controlled conditions, away from the damaging effects of sun, wind, and aridity.

    As DePalma worked around the paddlefish, more of the araucaria branch came to light, including its short, spiky needles. “This tree was alive when it was buried,” he said. Then he noticed a golden blob of amber stuck to the branch. Amber is preserved tree resin and often contains traces of whatever was in the air at the time, trapping the atmospheric chemistry and even, sometimes, insects and small reptiles. “This is Cretaceous flypaper,” he said. “I can’t wait to get this back to the lab.”

    An hour later, he had chiselled all the way around the fish, leaving it encased in matrix, supported by a four-inch-tall pedestal of rock. “I’m pretty sure this is a species new to science,” he said. Because the soft tissue had also fossilized, he said, even the animal’s stomach contents might still be present.

    He straightened up. “Time to plaster,” he said. He took off his shirt and began mixing a five-gallon bucket of plaster with his hands, while Pascucci tore strips of burlap. DePalma took a two-by-four and sawed off two foot-long pieces and placed them like splints on either side of the sediment-encased fossil. One by one, he dipped the burlap strips in the plaster and draped them across the top and the sides of the specimen. He added rope handles and plastered them in. An hour later, when the plaster had cured, he chiselled through the rock pedestal beneath the fossil and flipped the specimen over, leaving the underside exposed. Back in the lab, he would go through this surface to access the fossil, with the plaster jacket acting as a cradle below. Using the rope handles, DePalma and Pascucci lugged the specimen, which weighed perhaps two hundred pounds, to the truck and loaded it into the back. Later, DePalma would store it behind a friend’s ranch house, where all his jacketed fossils from the season were laid out in rows, covered with tarps.

    DePalma resumed digging. Gusts of wind stirred up clouds of dust, and rain fell; when the weather cleared, the late-afternoon sun spilled across the prairie. DePalma was lost in another day, in another time. “Here’s a piece of wood with bark-beetle traces,” he said. Plant fossils from the first several million years after the impact show almost no signs of such damage; the insects were mostly gone. The asteroid had likely struck in the fall, DePalma speculated. He had reached this conclusion by comparing the juvenile paddlefish and sturgeon he’d found with the species’ known growth rates and hatching seasons; he’d also found the seeds of conifers, figs, and certain flowers. “When we analyze the pollen and diatomaceous particles, that will narrow it down,” he said.

    A core sample from DePalma’s site. The site may hold a precise geological transcript of the asteroid strike that almost wiped out life on the planet. Photograph by Richard Barnes for The New Yorker.

    It solves the question of whether dinosaurs went extinct at exactly that level or whether they declined before,” the paleontologist Jan Smit said. “And this is the first time we see direct victims.” Photograph by Richard Barnes for The New Yorker.

    In the week that followed, fresh riches emerged: more feathers, leaves, seeds, and amber, along with several other fish, three to five feet long, and a dozen more craters with tektites. I have visited many paleontological sites, but I had never seen so many specimens found so quickly. Most digs are boring; days or weeks may pass with little found. DePalma seemed to make a noteworthy discovery about every half hour.

    When DePalma first visited the site, he noted, partially embedded on the surface, the hip bone of a dinosaur in the ceratopsian family, of which triceratops is the best-known member. A commercial collector had tried to remove it years earlier; it had been abandoned in place and was crumbling from years of exposure. DePalma initially dismissed it as “trash” and decried the irresponsibility of the collector. Later, though, he wondered how the bone, which was heavy, had arrived there, very close to the high-water mark of the flood. It must have floated, he said, and to have done so it must have been encased in desiccated tissue—suggesting that at least one dinosaur species was alive at the time of the impact. He later found a suitcase-size piece of fossilized skin from a ceratopsian attached to the hip bone.

    At one point, DePalma set off to photograph the layers of the deposit which had been cut through and exposed by the sandy wash. He scraped smooth a vertical section and misted it with water from a spray bottle to bring out the color. The bottom layer was jumbled; the first rush of water had ripped up layers of mud, gravel, and rocks and tumbled them about with pieces of burned (and burning) wood.

    Then DePalma came to a faint jug-shaped outline in the wall of the wash. He examined it closely. It started as a tunnel at the top of the KT layer, went down, and then widened into a round cavity, filled with soil of a different color, which stopped at the hard sandstone of the undisturbed bedrock layer below. It looked as though a small animal had dug through the mud to create a hideout. “Is that a burrow?” I asked.

    DePalma scraped the area smooth with his bayonet, then sprayed it. “You’re darn right it is,” he said. “And this isn’t the burrow of a small dinosaur. It’s a mammal burrow.” (Burrows have characteristic shapes, depending on the species that inhabit them.) He peered at it, his eyes inches from the rock, probing it with the tip of the bayonet. “Gosh, I think it’s still in there!”

    He planned to remove the entire burrow intact, in a block, and run it through a CT scanner back home, to see what it contained. “Any Cretaceous mammal burrow is incredibly rare,” he said. “But this one is impossible—it’s dug right through the KT boundary.” Perhaps, he said, the mammal survived the impact and the flood, burrowed into the mud to escape the freezing darkness, then died. “It may have been born in the Cretaceous and died in the Paleocene,” he said. “And to think—sixty-­six million years later, a stinky monkey is digging it up, trying to figure out what happened.” He added, “If it’s a new species, I’ll name it after you.”

    When I left Hell Creek, DePalma pressed me on the need for secrecy: I was to tell no one, not even close friends, about what he’d found. The history of paleontology is full of tales of bribery, backstabbing, and double-­dealing. In the nineteenth century, ­Othniel C. Marsh and Edward Drinker Cope, the nation’s two leading paleontologists, engaged in a bitter competition to collect dinosaur fossils in the American West. They raided each other’s quarries, bribed each other’s crews, and vilified each other in print and at scientific meetings. In 1890, the New York Herald began a series of sensational articles about the controversy with the headline “Scientists Wage Bitter Warfare.” The rivalry has since become known as the Bone Wars. The days of skulduggery in paleontology have not passed; DePalma was deeply concerned that the site would be expropriated by a major museum.

    DePalma knew that a screwup with this site would probably end his career, and that his status in the field was so uncertain that he needed to fortify the find against potential criticism. He had already experienced harsh judgment when, in 2015, he published a paper on a new species of dinosaur called a Dakotaraptor, and mistakenly inserted a fossil turtle bone in the reconstruction. Although rebuilding a skeleton from thousands of bone fragments that have commingled with those of other species is not easy, DePalma was mor­tified by the attacks. “I never want to go through that again,” he told me.

    For five years, DePalma continued excavations at the site. He quietly shared his findings with a half-dozen luminaries in the field of KT studies, including Walter Alvarez, and enlisted their help. During the winter months, when not in the field, DePalma prepared and analyzed his specimens, a few at a time, in a colleague’s lab at Florida Atlantic University, in Boca Raton. The lab was a windowless, wedge­like room in the geology building, lined with bubbling aquarium tanks and shelves heaped with books, scientific journals, pieces of coral, mastodon teeth, seashells, and a stack of .50-­calibre machine-gun rounds, dating from the Second World War, that the lab’s owner had recovered from the bottom of the Atlantic Ocean. DePalma had carved out a space for himself in a corner, just large enough for him to work on one or two jacketed fossils at a time.

    When I first visited the lab, in April, 2014, a block of stone three feet long by eighteen inches wide lay on a table under bright lights and a large magnifying lens. The block, DePalma said, contained a sturgeon and a paddlefish, along with dozens of smaller fossils and a single small, perfect crater with a tektite in it. The lower parts of the block consisted of debris, fragments of bone, and loose tektites that had been dislodged and caught up in the turbulence. The block told the story of the impact in microcosm. “It was a very bad day,” DePalma said. “Look at these two fish.” He showed me where the sturgeon’s scutes—the sharp, bony plates on its back—had been forced into the body of the paddlefish. One fish was impaled on the other. The mouth of the paddlefish was agape, and jammed into its gill rakers were microtektites—sucked in by the fish as it tried to breathe. DePalma said, “This fish was likely alive for some time after being caught in the wave, long enough to gasp frenzied mouthfuls of water in a vain attempt to survive.”

    Gradually, DePalma was piecing together a potential picture of the disaster. By the time the site flooded, the surrounding forest was already on fire, given the abundance of charcoal, charred wood, and amber he’d found at the site. The water arrived not as a curling wave but as a powerful, roiling rise, packed with disoriented fish and plant and animal debris, which, DePalma hypothesized, were laid down as the water slowed and receded.

    In the lab, DePalma showed me magnified cross-sections of the sediment. Most of its layers were horizontal, but a few formed curlicues or flamelike patterns called truncated flame structures, which were caused by a combination of weight from above and mini-surges in the incoming water. DePalma found five sets of these patterns. He turned back to the block on his table and held a magnifying lens up to the tektite. Parallel, streaming lines were visible on its surface—Schlieren lines, formed by two types of molten glass swirling together as the blobs arced through the atmosphere. Peering through the lens, DePalma picked away at the block with a dental probe. He soon exposed a section of pink, pearlescent shell, which had been pushed up against the sturgeon. “Ammonite,” he said. Ammonites were marine mollusks that somewhat resemble the present-day nautilus, although they were more closely related to squid and octopi. As DePalma uncovered more of the shell, I watched its vibrant color fade. “Live ammonite, ripped apart by the tsunami—they don’t travel well,” he said. “Genus Sphenodiscus, I would think.” The shell, which hadn’t previously been documented in the Hell Creek Formation, was another marine victim tossed inland.

    He stood up. “Now I’m going to show you something special,” he said, opening a wooden crate and removing an object that was covered in aluminum foil. He unwrapped a sixteen-inch fossil feather, and held it in his palms like a piece of Lalique glass. “When I found the first feather, I had about twenty seconds of disbelief,” he said. DePalma had studied under Larry Martin, a world authority on the Cretaceous predecessors of birds, and had been “exposed to a lot of fossil feathers. When I encountered this damn thing, I immediately understood the importance of it. And now look at this.”

    From the lab table, he grabbed a fossil forearm belonging to Dakotaraptor, the dinosaur species he’d discovered in Hell Creek. He pointed to a series of regular bumps on the bone. “These are probably quill knobs,” he said. “This dinosaur had feathers on its forearms. Now watch.” With precision calipers, he measured the diameter of the quill knobs, then the diameter of the quill of the fossil feather; both were 3.5 millimetres. “This matches,” he said. “This says a feather of this size would be associated with a limb of this size.”

    There was more, including a piece of a partly burned tree trunk with am­ber stuck to it. He showed me a photo of the amber seen through a micro­scope. Trapped inside were two impact particles—another landmark discovery, because the amber would have preserved their chemical composition. (All other tektites found from the impact, exposed to the elements for millions of years, have chemically changed.) He’d also found scores of beautiful examples of lonsdaleite, a hexagonal form of diamond that is associated with impacts; it forms when carbon in an asteroid is compressed so violently that it crystallizes into trillions of microscopic grains, which are blasted into the air and drift down.

    Finally, he showed me a photograph of a fossil jawbone; it belonged to the mammal he’d found in the burrow. “This is the jaw of Dougie,” he said. The bone was big for a Cretaceous mammal—three inches long—and almost complete, with a tooth. After my visit to Hell Creek, DePalma had removed the animal’s burrow intact, still encased in the block of sediment, and, with the help of some women who worked as cashiers at the Travel Center, in Bowman, hoisted it into the back of his truck. He believes that the jaw belonged to a marsupial that looked like a weasel. Using the tooth, he could conduct a stable-isotope study to find out what the animal ate—“what the menu was after the disaster,” he said. The rest of the mammal remains in the burrow, to be researched later.

    DePalma says that he’s discovered more than a dozen new species of animals and plants, and identified the broken teeth and bones, including hatchling remains, of almost every dinosaur group known from Hell Creek. Photograph by Richard Barnes for The New Yorker.

    DePalma listed some of the other discoveries he’s made at the site: several flooded ant nests, with drowned ants still inside and some chambers packed with microtektites; a possible wasp burrow; another mammal ­burrow, with multiple tunnels and galleries; shark teeth; the thigh bone of a large sea turtle; at least three new fish species; a gigantic ginkgo leaf and a plant that was a relative of the banana; more than a dozen new species of animals and plants; and several other burrow types.

    At the bottom of the deposit, in a mixture of heavy gravel and tektites, DePalma identified the broken teeth and bones, including hatchling remains, of almost every dinosaur group known from Hell Creek, as well as pterosaur remains, which had previously been found only in layers far below the KT boundary. He found, intact, an unhatched egg containing an embryo—a fossil of immense research value. The egg and the other remains suggested that dinosaurs and major reptiles were probably not staggering into extinction on that fateful day. In one fell swoop, DePalma may have solved the three-metre problem and filled in the gap in the fossil record.

    By the end of the 2013 field season, DePalma was convinced that the site had been created by an impact flood, but he lacked conclusive evidence that it was the KT impact. It was possible that it resulted from another giant asteroid strike that occurred at around the same time. “Extraordinary discoveries require extraordinary evidence,” he said. If his tektites shared the same geochemistry as tektites from the Chicxulub asteroid, he’d have a strong case. Deposits of Chicxulub tektites are rare; the best source, discovered in 1990, is a small outcrop in Haiti, on a cliff above a road cut. In late January, 2014, DePalma went there to gather tektites and sent them to an independent lab in Canada, along with tektites from his own site; the samples were analyzed at the same time, with the same equipment. The results indicated a near-perfect geochemical match.

    In the first few years after DePalma’s discoveries, only a handful of scientists knew about them. One was David Burnham, DePalma’s thesis adviser at Kansas, who estimates that DePalma’s site will keep specialists busy for at least half a century. “Robert’s got so much stuff that’s unheard of,” Burnham told me. “Amber with tektites embedded in it—holy cow! The dinosaur feathers are crazy good, but the burrow makes your head reel.” In paleontology, the term Lagerstätte refers to a rare type of fossil site with a large variety of specimens that are nearly perfectly preserved, a sort of fossilized ecosystem. “It will be a famous site,” Burnham said. “It will be in the textbooks. It is the Lagerstätte of the KT extinction.”

    Jan Smit, a paleontologist at Vrije University, in Amsterdam, and a world authority on the KT impact, has been helping DePalma analyze his results, and, like Burnham and Walter Alvarez, he is a co-author of a scientific paper that DePalma is publishing about the site. (There are eight other co-authors.) “This is really a major discovery,” Smit said. “It solves the question of whether dinosaurs went extinct at exactly that level or whether they declined before. And this is the first time we see direct victims.” I asked if the results would be controversial. “When I saw his data with the paddlefish, sturgeon, and ammonite, I think he’s right on the spot,” Smit said. “I am very sure he has a pot of gold.”

    In September of 2016, DePalma gave a brief talk about the discovery at the annual meeting of the Geological Society of America, in Colorado. He mentioned only that he had found a deposit from a KT flood that had yielded glass droplets, shocked minerals, and fossils. He had christened the site Tanis, after the ancient city in Egypt, which was featured in the 1981 film “Raiders of the Lost Ark” as the resting place of the Ark of the Covenant. In the real Tanis, archeologists found an inscription in three writing systems, which, like the Rosetta stone, was crucial in translating ancient Egyptian. DePalma hopes that his Tanis site will help decipher what happened on the first day after the impact.

    The talk, limited though it was, caused a stir. Kirk Cochran, a professor at the School of Marine and Atmospheric Science at Stony Brook University, in New York, recalled that when DePalma presented his findings there were gasps of amazement in the audience. Some scientists were wary. Kirk Johnson, the director of the Smithsonian’s National Museum of Natural History, told me that he knew the Hell Creek area well, having worked there since 1981. “My warning lights were flashing bright red,” he told me. “I was so skeptical after the talk I was convinced it was a fabrication.” Johnson, who had been mapping the KT layer in Hell Creek, said that his research indicated that Tanis was at least forty-five feet below the KT boundary and perhaps a hundred thousand years older. “If it’s what it’s said to be,” Johnson said, “it’s a fabulous discovery.” But he declared himself “uneasy” until he could see DePalma’s paper.

    One prominent West Coast paleontologist who is an authority on the KT event told me, “I’m suspicious of the findings. They’ve been presented at meetings in various ways with various associated extraordinary claims. He could have stumbled on something amazing, but he has a reputation for making a lot out of a little.” As an example, he brought up DePalma’s paper on Dakotaraptor, which he described as “bones he basically collected, all in one area, some of which were part of a dinosaur, some of which were part of a turtle, and he put it all together as a skeleton of one animal.” He also objected to what he felt was excessive secrecy surrounding the Tanis site, which has made it hard for outside scientists to evaluate DePalma’s claims.

    Johnson, too, finds the lack of transparency, and the dramatic aspects of DePalma’s personality, unnerving. “There’s an element of showmanship in his presentation style that does not add to his credibility,” he said. Other paleontologists told me that they were leery of going on the record with criticisms of DePalma and his co-authors. All expressed a desire to see the final paper, which will be published next week, in the Proceedings of the National Academy of Sciences, so that they could evaluate the data for themselves.

    After the G.S.A. talk, DePalma realized that his theory of what had happened at Tanis had a fundamental problem. The KT tsunami, even moving at more than a hundred miles an hour, would have taken many hours to travel the two thousand miles to the site. The rainfall of glass blobs, however, would have hit the area and stopped within about an hour after the impact. And yet the tektites fell into an active flood. The timing was all wrong.

    This was not a paleontological question; it was a problem of geophysics and sedimentology. Smit was a sedimentologist, and another researcher whom DePalma shared his data with, Mark Richards, now of the University of Washington, was a geophysicist. At dinner one evening in Nagpur, India, where they were attending a conference, Smit and Richards talked about the problem, looked up a few papers, and later jotted down some rough calculations. It was immediately apparent to them that the KT tsunami would have arrived too late to capture the falling tektites; the wave would also have been too diminished by its long journey to account for the thirty-­five-foot rise of water at Tanis. One of them proposed that the wave might have been created by a curious phenomenon known as a seiche. In large earthquakes, the shaking of the ground sometimes causes water in ponds, swimming pools, and bathtubs to slosh back and forth. Richards recalled that the 2011 Japanese earthquake produced bizarre, five-foot seiche waves in an absolutely calm Norwegian fjord thirty minutes after the quake, in a place unreachable by the tsunami.

    Richards had previously estimated that the worldwide earthquake generated by the KT impact could have been a thousand times stronger than the biggest earthquake ever experienced in human history. Using that gauge, he calculated that potent seismic waves would have arrived at Tanis six minutes, ten minutes, and thirteen minutes after the impact. (Different types of seismic waves travel at different speeds.) The brutal shaking would have been enough to trigger a large seiche, and the first blobs of glass would have started to rain down seconds or minutes afterward. They would have continued to fall as the seiche waves rolled in and out, depositing layer upon layer of sediment and each time ­sealing the tektites in place. The Tanis site, in short, did not span the first day of the impact: it probably recorded the first hour or so. This fact, if true, renders the site even more fabulous than previously thought. It is almost beyond credibility that a precise geological transcript of the most important sixty minutes of Earth’s history could still exist millions of years later—a sort of high-speed, high-resolution video of the event recorded in fine layers of stone. DePalma said, “It’s like finding the Holy Grail clutched in the bony fingers of Jimmy Hoffa, sitting on top of the Lost Ark.” If Tanis had been closer to or farther from the impact point, this beautiful coincidence of timing could not have happened. “There’s nothing in the world that’s ever been seen like this,” Richards told me.

    One day sixty-six million years ago, life on Earth almost came to a shattering end. The world that emerged after the impact was a much simpler place. When sunlight finally broke through the haze, it illuminated a hellish landscape. The oceans were empty. The land was covered with drifting ash. The forests were charred stumps. The cold gave way to extreme heat as a greenhouse effect kicked in. Life mostly consisted of mats of algae and growths of fungus: for years after the impact, the Earth was covered with little other than ferns. Furtive, ratlike mammals lived in the gloomy understory.

    But eventually life emerged and blossomed again, in new forms. The KT event continues to attract the interest of scientists in no small part because the ashen print it left on the planet is an existential reminder. “We wouldn’t be here talking on the phone if that meteorite hadn’t fallen,” Smit told me, with a laugh. DePalma agreed. For the first hundred million years of their existence, before the asteroid struck, mammals scurried about the feet of the dinosaurs, amounting to little. “But when the dinosaurs were gone it freed them,” DePalma said. In the next epoch, mammals underwent an explosion of adaptive radiation, evolving into a dazzling variety of forms, from tiny bats to gigantic titanotheres, from horses to whales, from fearsome creodonts to large-brained primates with hands that could grasp and minds that could see through time.

    “We can trace our origins back to that event,” DePalma said. “To actually be there at this site, to see it, to be connected to that day, is a special thing. This is the last day of the Cretaceous. When you go one layer up—the very next day—that’s the Paleocene, that’s the age of mammals, that’s our age.”

    See the full article here .


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  • richardmitnick 7:57 am on March 22, 2019 Permalink | Reply
    Tags: Burgess Shale in Canada, Cambrian explosion of life, , , Paleontology, Qingjiang and Chengjiang fossils in China,   

    From Science News: “Newfound fossils in China highlight a dizzying diversity of Cambrian life” 

    From Science News

    March 21, 2019
    Carolyn Gramling

    ANCIENT IMPRINTS The newly described Qingjiang biota, a rich fossil site dating to about 518 million years ago, helps document a rapid flourishing of diverse invertebrate life known as the Cambrian explosion. The fossils include abundant jellyfish (left) and comb jellies (middle), as well as a segmented, spiny animal that may be a kinorhynch (right).

    Along the banks of China’s Danshui River lies a treasure trove of fossils that may rival the most famous Cambrian fossil assemblage of all, Canada’s Burgess Shale. The roughly 518-million-year-old site contains a dizzying abundance of beautifully preserved weird and wonderful life-forms, from jellyfish and comb jellies to arthropods and algae.

    So far, researchers led by paleontologist Dongjing Fu of Northwest University in Xian, China, have collected 4,351 specimens at the new site, representing 101 different taxa, or groups of organisms. Of those taxa, about 53 percent have never before been observed, Fu and her colleagues report in the March 22 Science — not even at other well-known Cambrian fossil sites such as the 508-million-year-old Burgess Shale or a 518-million-year-old site known as Chengjiang, also in China.

    “It’s an exciting discovery,” says Jean-Bernard Caron, a paleontologist at the Royal Ontario Museum in Toronto who wasn’t involved in the study. During the Cambrian Period, which began about 542 million years ago, life diversified extremely rapidly. So many new forms appeared in such a relatively short period of time that this diversification is known as the Cambrian explosion. The find “shows that there’s hope for new discoveries” of other Cambrian fossil sites, he says.

    FOSSIL FINDS Researchers discovered the Qingjiang fossils along the bank of China’s Danshui River in Hubei Province. Dong King Fu

    Such sites represent snapshots of life long ago, and no one site can portray the true diversity of life on Earth at any given time, Caron says. “It’s a giant jigsaw puzzle, and we only have a few pieces…. But the more pieces we have, the better chance we have to understand life during that time.”

    The new fossil trove, called the Qingjiang biota, was first spotted in 2007, says coauthor Xingliang Zhang, a paleontologist also at Northwest University. “I have been working on Burgess Shale–type fossils for many years, and know what kind of rocks preserve [them],” Zhang says.

    During a field expedition that year, he and his students were investigating a different rock layer dating to the Cambrian. At lunchtime, he says, he happened to sit on the next lower layer of rocks as it was being lapped by the river’s water — and immediately recognized that the fine clay layer was the perfect preservation setting for fossils. “We split the clay stone and I found a Leanchoilia [a kind of segmented arthropod] quickly.” Many more discoveries soon followed.

    The site is remarkable for the quality of the preservation of the animals, says Allison Daley, a paleontologist at the University of Lausanne in Switzerland who was not involved in the new study but wrote a Science commentary that accompanies it in Science. “There was very little metamorphism or weathering effect, which does affect some other [Cambrian fossil] sites, like Burgess or Chengjiang. We see almost pristine fossils at this site.” She mentions one startlingly clear image of a jellyfish. “I mean, if you were going to smack a jellyfish on a rock, that’s how it would look.”

    Weird wonders
    The excellent preservation of the Qingjiang fossils reveals fine morphological details of some of the life-forms that lived in Cambrian seas, such as a branched alga (left) and the segmented body of an arthropod called a megacherian (right).

    Unlike other Cambrian fossil troves, the Qingjiang biota appears to contain a high proportion of jellyfish, or cnidarians, and comb jellies, also called ctenophores. These species, particularly the comb jellies, are extremely rare at other sites.

    With so many ctenophore fossils preserved so well, Daley says, studying their shapes may help to answer a long-standing debate: Whether comb jellies or sponges are the most primitive animal on their family tree. Scientists have thought that sponges appear closer to the base of the tree, based on their very simple shapes. But some molecular analyses have hinted that comb jellies may be at the base of the tree.

    “It’s hard to disentangle the exact relationships of these [creatures],” Daley says. “These early branching groups diverged from each other such a long time ago…. So getting more info on [them] at this new site, where the preservation is really amazing, is really going to fill a gap.”

    The Burgess Shale, a vast deposit of fossil-bearing rocks in the Canadian Rockies, was discovered in 1909. It was this site that first gave scientists a glimpse into the Cambrian explosion, the rapid diversification of life that occurred during that period. The Burgess and Chengjiang sites, separated by 10 million years and half a world today, share only about 15 percent of the same taxa.

    That might be expected, Daley says, given their differences in both space and time. But the Qingjiang and Chengjiang sites, which date to the same time period and are separated by only 1,050 kilometers today, share only 8 percent of their taxa, she says. The researchers, however, suggest that the Qingjiang site may have been a slightly deeper marine environment. If so, that difference in ancient environment may have been the reason why the assemblage of creatures is so different, Daley says.

    The new work is preliminary, representing just the first of what is likely to be a deluge of studies describing fossils found at the site, Zhang says. “We’re just beginning!”

    Even after 110 years of digging in the Burgess Shale region, paleontologists are still turning up rich new sites and bizarre new creatures, adds Caron, of Canada’s Royal Ontario Museum. Just last summer, he and colleagues made new discoveries, including an enigmatic shield-shaped critter that he dubbed “the mothership.” Unlike other Cambrian fossil troves, the Qingjiang biota appears to contain a high proportion of jellyfish, or cnidarians, and comb jellies, also called ctenophores. These species, particularly the comb jellies, are extremely rare at other sites.

    With so many ctenophore fossils preserved so well, Daley says, studying their shapes may help to answer a long-standing debate: Whether comb jellies or sponges are the most primitive animal on their family tree. Scientists have thought that sponges appear closer to the base of the tree, based on their very simple shapes. But some molecular analyses have hinted that comb jellies may be at the base of the tree.

    “It’s hard to disentangle the exact relationships of these [creatures],” Daley says. “These early branching groups diverged from each other such a long time ago…. So getting more info on [them] at this new site, where the preservation is really amazing, is really going to fill a gap.”

    The Burgess Shale, a vast deposit of fossil-bearing rocks in the Canadian Rockies, was discovered in 1909. It was this site that first gave scientists a glimpse into the Cambrian explosion, the rapid diversification of life that occurred during that period. The Burgess and Chengjiang sites, separated by 10 million years and half a world today, share only about 15 percent of the same taxa.

    That might be expected, Daley says, given their differences in both space and time. But the Qingjiang and Chengjiang sites, which date to the same time period and are separated by only 1,050 kilometers today, share only 8 percent of their taxa, she says. The researchers, however, suggest that the Qingjiang site may have been a slightly deeper marine environment. If so, that difference in ancient environment may have been the reason why the assemblage of creatures is so different, Daley says.

    The new work is preliminary, representing just the first of what is likely to be a deluge of studies describing fossils found at the site, Zhang says. “We’re just beginning!”

    Even after 110 years of digging in the Burgess Shale region, paleontologists are still turning up rich new sites and bizarre new creatures, adds Caron, of Canada’s Royal Ontario Museum. Just last summer, he and colleagues made new discoveries, including an enigmatic shield-shaped critter that he dubbed “the mothership.”

    See the full article here .


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  • richardmitnick 5:25 pm on March 13, 2019 Permalink | Reply
    Tags: , , , Comet, Controversial from the time it was proposed the hypothesis even now continues to be contested by those who prefer to attribute the end-Pleistocene reversal in warming entirely to terrestrial causes., , , Kennett and fellow stalwarts of the Younger Dryas Boundary (YDB) Impact Hypothesis have recently received a major boost:, Paleontology, The discovery of a very young 31-kilometer-wide impact crater beneath the Greenland ice sheet which they believe may have been one of the many comet fragments that impacted Earth at the onset of the Y, The layer containing these spherules also show peak concentrations of platinum and gold and native iron particles rarely found in nature, The Pilauco dig site in a suburb of the Osorno province in Chile, The presence of microscopic spherules interpreted to have been formed by melting due to the extremely high temperatures associated with impact, They believe this may have been one of the many comet fragments that impacted Earth at the onset of the Younger Dryas., UC Santa Barbara geology professor emeritus James Kennett, , Younger Dryas Impact Hypothesis   

    From UC Santa Barbara: “The Day the World Burned” 

    UC Santa Barbara Name bloc
    From UC Santa Barbara

    March 8, 2019
    Sonia Fernandez

    The researchers found evidence of cosmic impact at the Pilauco dig site in a suburb of the Osorno province in Chile. Photo Credit: Courtesy Image

    When UC Santa Barbara geology professor emeritus James Kennett and colleagues set out years ago to examine signs of a major cosmic impact that occurred toward the end of the Pleistocene epoch, little did they know just how far-reaching the projected climatic effect would be.

    James Kennett. Photo Credit: Sonia Fernandez

    “It’s much more extreme than I ever thought when I started this work,” Kennett noted. “The more work that has been done, the more extreme it seems.”

    He’s talking about the Younger Dryas Impact Hypothesis, which postulates that a fragmented comet slammed into the Earth close to 12,800 years ago, causing rapid climatic changes, megafaunal extinctions, sudden human population decrease and cultural shifts and widespread wildfires (biomass burning). The hypothesis suggests a possible triggering mechanism for the abrupt changes in climate at that time, in particular a rapid cooling in the Northern Hemisphere, called the Younger Dryas, amid a general global trend of natural warming and ice sheet melting evidenced by changes in the fossil and sediment record.

    Controversial from the time it was proposed, the hypothesis even now continues to be contested by those who prefer to attribute the end-Pleistocene reversal in warming entirely to terrestrial causes. But Kennett and fellow stalwarts of the Younger Dryas Boundary (YDB) Impact Hypothesis, as it is also known, have recently received a major boost: the discovery of a very young, 31-kilometer-wide impact crater beneath the Greenland ice sheet, which they believe may have been one of the many comet fragments that impacted Earth at the onset of the Younger Dryas.

    Now, in a paper published in the journal Nature Scientific Reports, Kennett and colleagues, led by Chilean paleontologist Mario Pino, present further evidence of a cosmic impact, this time far south of the equator, that likely lead to biomass burning, climate change and megafaunal extinctions nearly 13,000 years ago.

    “We have identified the YDB layer at high latitudes in the Southern Hemisphere at near 41 degrees south, close to the tip of South America,” Kennett said. This is a major expansion of the extent of the YDB event.” The vast majority of evidence to date, he added, has been found in the Northern Hemisphere.

    This discovery began several years ago, according to Kennett, when a group of Chilean scientists studying sediment layers at a well-known Quaternary paleontological and archaeological site, Pilauco Bajo, recognized changes known to be associated with YDB impact event. They included a “black mat” layer, 12,800 years in age, that coincided with the disappearance of South American Pleistocene megafauna fossils, an abrupt shift in regional vegetation and a disappearance of human artifacts.

    “Because the sequencing of these events looked like what had already been described in the YDB papers for North America and Western Europe, the group decided to run analyses of impact-related proxies in search of the YDB layer,” Kennett said. This yielded the presence of microscopic spherules interpreted to have been formed by melting due to the extremely high temperatures associated with impact. The layer containing these spherules also show peak concentrations of platinum and gold, and native iron particles rarely found in nature.

    “Among the most important spherules are those that are chromium-rich,” Kennett explained. The Pilauco site spherules contain an unusual level of chromium, an element not found in Northern Hemisphere YDB impact spherules, but in South America. “It turns out that volcanic rocks in the southern Andes can be rich in chromium, and these rocks provided a local source for this chromium,” he added. “Thus, the cometary objects must have hit South America as well.”

    Other evidence, which, Kennett noted, is consistent with previous and ongoing documentation of the region by Chilean scientists, pointed to a “very large environmental disruption at about 40 degrees south.” These included a large biomass burning event evidenced by, among other things, micro-charcoal and signs of burning in pollen samples collected at the impact layer. “It’s by far the biggest burn event in this region we see in the record that spans thousands of years,” Kennett said. Furthermore, he went on, the burning coincides with the timing of major YDB-related burning events in North America and western Europe.

    The sedimentary layers at Pilauco contain a valuable record of pollen and seeds that show change in character of regional vegetation — evidence of a shifting climate. However, in contrast to the Northern Hemisphere, where conditions became colder and wetter at the onset of the Younger Dryas, the opposite occurred in the Southern Hemisphere.

    “The plant assemblages indicate that there was an abrupt and major shift in the vegetation from wet, cold conditions at Pilauco to warm, dry conditions,” Kennett said. According to him, the atmospheric zonal climatic belts shifted “like a seesaw,” with a synergistic mechanism, bringing warming to the Southern Hemisphere even as the Northern Hemisphere experienced cooling and expanding sea ice. The rapidity — within a few years — with which the climate shifted is best attributed to impact-related shifts in atmospheric systems, rather than to the slower oceanic processes, Kennett said.

    Meanwhile, the impact with its associated major environmental effects, including burning, is thought to have contributed to the extinction of local South American Pleistocene megafauna — including giant ground sloths, sabretooth cats, mammoths and elephant-like gomphotheres — as well as the termination of the culture similar to the Clovis culture in the north, he added. The amount of bones, artifacts and megafauna-associated fungi that were relatively abundant in the soil at the Pilauco site declined precipitously at the impact layer, indicating a major local disruption.

    The distance of this recently identified YDB site — about 6,000 kilometers from the closest well-studied site in South America — and its correlation with the many Northern Hemispheric sites “greatly expands the extent of the YDB impact event,” Kennett said. The sedimentary and paleo-vegetative evidence gathered at the Pilauco site is in line with previous, separate studies conducted by Chilean scientists that indicate a widespread burn and sudden major climate shifts in the region at about YDB onset. This new study further bolsters the hypothesis that a cosmic impact triggered the atmospheric and oceanic conditions of the Younger Dryas, he said.

    “This is further evidence that the Younger Dryas climatic onset is an extreme global event, with major consequences on the animal life and the human life at the time,” Kennett said. “And this Pilauco section is consistent with that.”

    Research on this study was also conducted by Ana Abarzúa, Giselle Astorga, Alejandra Martel-Cea, Nathalie Cossio, Maria Paz Lira and Rafael Labarca of Universidad Austral de Chile; R. Ximena Navarro of Universidad Católica de Temuco; and Malcolm A. LeCompte and Victor Adedeji of Elizabeth City State University. Christopher Moore of University of South Carolina; Ted E. Bunch and Charles Mooney of Northern Arizona University; and Wendy S. Wolbach of DePaul University contributed research, as did Allen West of Comet Research Group.

    See the full article here .

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    The University of California, Santa Barbara (commonly referred to as UC Santa Barbara or UCSB) is a public research university and one of the 10 general campuses of the University of California system. Founded in 1891 as an independent teachers’ college, UCSB joined the University of California system in 1944 and is the third-oldest general-education campus in the system. The university is a comprehensive doctoral university and is organized into five colleges offering 87 undergraduate degrees and 55 graduate degrees. In 2012, UCSB was ranked 41st among “National Universities” and 10th among public universities by U.S. News & World Report. UCSB houses twelve national research centers, including the renowned Kavli Institute for Theoretical Physics.

  • richardmitnick 1:42 pm on March 22, 2016 Permalink | Reply
    Tags: , , , Paleontology,   

    From UNSW: “A golden age of ancient DNA science begins” 

    U NSW bloc

    University of New South Wales

    22 Mar 2016
    Darren Curnoe

    A reconstruction of a male our evolutionary cousin the Neanderthals (Modified from an image by Cicero Moraes). Wikimedia Commons, CC BY-SA

    OPINION: If I had taken a straw poll among anthropologists 10 years ago asking them how far genetic research would come in the next decade, I doubt anyone would have come close to predicting the big impact fossil DNA work would come to have.

    Back then, this nascent field was bogged down with fundamental issues like distinguishing authentic DNA from contamination. Simply recovering enough nuclear DNA to say anything sensible at all about human origins would have been a really big achievement.

    But following some remarkable technical developments in that time, including next generation sequencing, ancient DNA research is beginning to come of age.

    And it’s no exaggeration to say that it’s dramatically rewriting our understanding of the human evolutionary story and, unexpectedly, resolving some old, seemingly intractable, questions along the way.

    I say ‘beginning’ because despite the remarkable findings over the last half decade or so, many of which I have written about before, ancient DNA, particularly fossil genome research, has really only just begun.

    But, boy, what start!

    Two studies out last week in the journals Science and Nature are characteristic of the coming of age of ancient DNA studies; I’ll return to them shortly.

    As I see it – from the viewpoint of someone who studies the fossils – this field is beginning to provide answers to some big questions we’ve been wrestling with for a long, long, time.

    Here are three big issues which I think geneticists are making headway on, following decades of stalled progress by fossil specialists.

    1. There’s been a shift from merely documenting the occurrence of interbreeding between modern humans and archaic groups, like the Neanderthals and Denisovans, to a focus on the circumstances surrounding it and its consequences for living people.

    A few years back we fossil-jocks couldn’t agree about whether interbreeding had actually occurred or not. The case now seems to be closed thanks to the geneticists.

    Interbreeding occurred, but it wasn’t terribly common. Around 2 per cent of the genome of non-African people was inherited from Neanderthals, with slightly more DNA in Indigenous Oceanic Southeast Asians, New Guineans and Australians coming from the mysterious Denisovans (on top of their Neanderthal inheritance).

    Even among some living African populations, there is evidence for DNA inherited from an archaic species living on that continent perhaps as late as 30 thousand years ago.

    I suspect there will be more evidence found in the future, from other, perhaps as yet unknown, archaic species.

    One of the new studies – led by Benjamin Vernot from the University of Washington – examined 35 new genomes sequenced from people living in 11 locations in the Bismarck Archipelago of New Guinea to get a better handle on gene sharing with our archaic cousins.

    They confirmed evidence for ancient gene flow with the Neanderthals and have better characterised mating with the mysterious Denisovans, by comparing their new genomes with around 1,500 other human samples.

    The New Guinean samples showed between 1.9 and 3.4 per cent of their genomes to be derived from the Deniosvans.

    They also showed that a second ‘pulse’ of interbreeding is seen among living East Asians, Europeans and South Asians that wasn’t shared with New Guineans.

    There were seemingly three separate interbreeding events with the Neanderthals: one with the ancestors of New Guineans and Australians, one with early East Asians and one with the ancestors of South Asians and Europeans.

    Geneticists have now turned their attention to the specific genes that have been inherited by living humans from our archaic cousins and their consequences for understanding human adaptations and disease.

    I’ve looked at some of these previously, like those associated with the human immune system and high altitude adaptation.

    The really exciting area to be explored in the future is whether genes associated with features of the skeleton can be identified, helping us to make a direct connection with the physical changes documented in the fossil record and to understand how and why such changes came about.

    2. Ancient DNA is finally placing a framework around the vexed question, ‘how can we pick a new species from among the fossils’?

    For decades, anthropologists have been locking horns over how many species there might be in the human evolutionary tree; with estimates presently ranging from 5 to more than 25 species.

    So far, we’ve lacked an independent, objective, way to test our ideas. But, surprisingly, this is now emerging from comparisons of the human genome with those of our archaic cousins.

    For example, for over 100 years anthropologists have argued about whether the Neanderthals are a separate species to modern humans, or merely a sub-species of our kind.

    DNA has now given us an answer, and it should satisfy even the more hard nosed of anthropologists; although, experience tells me some of my colleagues will go the grave believing otherwise.

    Neanderthal, Denisovan and other archaic DNA is found unevenly throughout the human genome, occurring in hotspots, with vast deserts separating large stretches of archaic genes.

    One example is the human X-chromosome which is largely free of archaic DNA. This indicates that natural selection weeded out archaic genes, and also that male hybrid offspring of archaic and modern human matings were probably infertile.

    Anyone with a passing interest in the species questions will recognise immediately the importance of such a finding: humans and Neanderthals were different species, even if one applies the very strict criterion of ‘interbreeding’, so widely assumed to be indicative of species differences.

    Now, most anthropologists have considered the Neanderthals to be the closest extinct relative we humans have, regardless of their species status. Yet, DNA work shows they were highly biologically distinct from us, in accordance, as I see it, with their unusual physical features.

    To me, this indicates we should be prepared to recognise and accommodate many more species in the human tree, even after humans and Neanderthal had split.

    You might like to read my article about the complex question of species and their recognition in human evolution studies.

    3. Fossil DNA is now sorting out evolutionary relationships among human species.

    The second study from last week, led by Matthias Meyer of the Max Planck Institute for Evolutionary Anthropology, recovered nuclear DNA from two specimens from the Spanish fossil site of Sima de Los Huesos (the ‘pit of bones’).

    These fossils are at least 430 thousand years old, and the new work builds on research by the team published last year where they were able to recover the much smaller and less informative mitochondrial genome from a fossil from the site.

    The mitochondrial DNA was found to be identical to the Deniosvans, but the new nuclear sequences are related to Neanderthals.

    So, the Sima de Los Huesos specimens are either very early Neanderthals or the ancestors of the Neanderthals; retaining the mitochondrial genome of their Denisovan ancestors, or perhaps even acquiring it through interbreeding.

    The work confirms nicely what some anthropologists have thought about the Sima de Los Huesos fossils from their anatomy.

    It also shows that the common ancestor of Neanderthals and modern humans lived more than 430 thousand years ago; in fact, the molecular clock in this new research indicates a split somewhere in the range of 550-765 thousand years ago.

    This means that the immediate ancestors of living humans evolved for at least 600 thousand years, probably longer, separately from the Neanderthals.

    I take away from this that it takes about 600 thousand years for hybrid sterility to kick in in humans. And, remembering that hybrid sterility is at the end of the process of species formation, we should expect there to be many more, short-lived, species in the human tree than we’ve recognised until now.

    Human evolution should be seen as a bush, with lot’s of twigs, rather than a thickly trunked tree, with only a small number of branches (species). I imagine diversity was the rule as we see in other living primates today.

    We modern humans were just one of many kinds of human, but oddly, the only one to persist today. Perhaps genomics might help us answer this mother of all mysteries in the not too distant future as well.

    See the full article here .

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    In developing new ideas and promoting lasting knowledge we are creating an academic environment where outstanding students and scholars from around the world can be inspired to excel in their programs of study and research. Partnerships with both local and global communities allow UNSW to share knowledge, debate and research outcomes. UNSW’s public events include concert performances, open days and public forums on issues such as the environment, healthcare and global politics. We encourage you to explore the UNSW website so you can find out more about what we do.

  • richardmitnick 11:42 am on January 21, 2016 Permalink | Reply
    Tags: , , Paleontology, Sean_B._Carroll, The Day the Mesozoic Died   

    From Nautilus: “The Day the Mesozoic Died” 



    January 21, 2016
    Sean B. Carroll

    Temp 1

    “Understanding how we decipher a great historical event written in the book of rocks
    may be as interesting as the event itself.”
    —Walter Alvarez

    Built upon the slopes of Mount Ingino in Umbria, the ancient town of Gubbio boasts many well-preserved structures that document its glorious history. Founded by the Etruscans between the second and first centuries B.C., its Roman theater, Consuls Palace, and various churches and fountains are spectacular monuments to the Roman, Medieval, and Renaissance periods. It is one of those special destinations that draws tourists to this famous part of Italy.

    It was not the ancient architecture but the much longer natural history preserved in the rock formations outside the city walls that brought Walter Alvarez, a young American geologist, to Gubbio. Just outside the town lay a geologist’s dream—one of the most extensive, continuous limestone rock sequences anywhere on the planet (See Father and Son). The “Scaglia rossa” is the local name for the attractive pink outcrops found along the mountainsides and gorges of the area (“Scaglia” means scale or flake and refers to how the rock is easily chipped into the square blocks used for buildings, such as the Roman theater. “Rossa” refers to the pink color). The massive formation is composed of many layers that span about 400 meters in total. Once an ancient seabed, the rocks represent some 50 million years of Earth’s history.

    Watch and download mp4 video here .
    The Death of the Dinosaurs: The disappearance of the dinosaurs at the end of the Cretaceous period represented a long-standing scientific mystery. This three-act film tells the story of the extraordinary detective work that solved it. Howard Hughes Medical Institute

    Geologists have long used fossils to help identify parts of the rock record from around the world and Walter employed this strategy in studying the formations around Gubbio. Throughout the limestone he found fossilized shells of tiny creatures, called foraminifera or “forams” for short, a group of single-celled protists that can only be seen with a magnifying lens. But in one centimeter of clay that separated two limestone layers, he found no fossils at all. Furthermore, in the older layer below the clay, the forams were more diverse and much larger than in the younger layer above the clay (See Foraminifera). Everywhere he looked around Gubbio, he found that thin layer of clay and the same difference between the forams below and above it.

    Temp 2
    Father and Son: Luis (left) and Walter Alvarez at a limestone outcrop near Gubbio, Italy. Walter’s right hand is touching the top of the Cretaceous limestone, at the K-T boundary. Courtesy of Lawrence Berkeley National Laboratory

    Walter was puzzled. What had happened to cause such a change in the forams? How fast did it happen? How long a period of time did that thin layer without forams represent?

    These questions about seemingly mundane microscopic creatures and one centimeter of clay in a 1,300-foot-thick rock bed in Italy might appear to be trivial. But their pursuit led Walter to a truly Earth-shattering discovery about one of the most important days in the history of life.

    Temp 3
    Foraminifera : Walter Alvarez was puzzled by the rapid, dramatic change in foram size between the end of the Cretaceous (pictured at the bottom here) and the beginning of the Tertiary (top) periods, which is seen worldwide. These specimens are from a different location (not Gubbio). Images courtesy of Brian Huber, Smithsonian Museum of Natural History

    The K-T Boundary

    From the distribution of fossils and other geological data, it was known that the Gubbio formation spanned parts of both the Cretaceous [usually abbreviated K for its German translation Kreide (chalk)] and Tertiary periods. The names of these and other geological time periods come from early geologists’ ideas about the major intervals in Earth history, and from some of the features that mark particular times. In one scheme, the history of life is divided into three eras—the Paleozoic (“ancient life,” the first animals), the Mesozoic (“middle life,” the age of dinosaurs), and the Cenozoic (“recent life,” the age of mammals). The Cretaceous period, named after characteristic chalky deposits, forms the last third of the Mesozoic era. The Tertiary period (which has been renamed and subdivided into the Paleogene and Neogene) begins at the end of the Cretaceous 65 million years ago and ends at the beginning of the Quaternary period 2.6 million years ago.

    Temp 4
    Geologic time scale: Geologists organize Earth’s history into eras and periods. The KT boundary falls right at the border of the Cretaceous period and the Tertiary period, around 65 million years ago.

    Walter and his colleague Bill Lowrie spent several years studying the Gubbio formation, sampling up from the Tertiary and down through the Cretaceous. They were first interested in trying to correlate reversals in the Earth’s magnetic field with the fossil record as a way of deciphering the time-scale of Earth’s history. They learned to figure out where they were in the rock formation by the forams characteristic of certain deposits, and by learning to recognize the boundary between the Cretaceous and Tertiary rocks. That boundary was always right where the dramatic reduction in foram diversity size occurred. The rocks below were Cretaceous and the rocks above were Tertiary, and the thin layer of clay was in the gap between (See The K-T Boundary at Gubbio). The boundary is referred to as the K-T boundary.

    One thousand kilometers from Gubbio, at Caravaca on the southeast coast of Spain, a Dutch geologist, Jan Smit, had noticed a similar pattern of changes in forams in rocks around the K-T boundary. Smit knew that the K-T boundary marked the most famous extinction of all—the dinosaurs. When a colleague pointed out that fact to Walter, he became even more interested in those little forams and the K-T boundary.

    Temp 5
    The K-T boundary at Gubbio: The white Cretaceous limestone is separated from the reddish Tertiary limestone by a thin clay layer (marked with coin). Courtesy of Frank Schonian, Museum of Natural History, Berlin

    Walter was relatively new to academic geology. After he received his Ph.D. he had worked for the exploration arm of a multinational oil company in Libya, until Colonel Qaddafi expelled all of the Americans out of the country. His work on magnetic reversals had gone well but he realized that the abrupt change in the Gubbio forams and the K-T extinction presented a much bigger mystery that he became determined to solve.

    One of the first questions Walter wanted to answer, naturally, was how long it took for that thin clay layer to form? To answer this he would need some help. It is very common for children to get help from their parents with their science projects. However, it is extremely unusual, as it was in Walter’s case, that the “child” is in their late 30s. But few children of any age had a Dad like Walter’s.

    From A-Bombs to Cosmic Rays

    Luis Alvarez knew very little about geology or paleontology but he knew a lot about physics. He was a central figure in the birth and growth of nuclear physics. He received his Ph.D. in physics in 1936 from the University of Chicago and worked at the University of California, Berkeley under Ernest Lawrence, the recipient of the 1939 Nobel Prize in Physics for the invention of the cyclotron.

    His early work in physics was interrupted by the onset of World War II. During the first years of the war, Luis worked on the development of radar and systems that would help airplanes land safely in poor visibility. He received the Collier Trophy, the highest honor in aviation, for developing the Ground Controlled Approach (GCA) system for bad weather landings.

    In the middle of the war, he was recruited into the Manhattan Project, the top secret national effort to develop atomic weapons. Alvarez and his student Lawrence Johnston designed detonators for the bombs. Robert Oppenheimer, the director of the Manhattan Project, then put him in charge of measuring the energy released by the bombs. Luis was one of the very few to witness the first two atomic blasts. He flew as a scientific eyewitness to the first test of the atomic bomb in the New Mexico desert and then shortly thereafter to the bomb dropped on Hiroshima, Japan.

    After the war, Luis returned to physics research. He developed the use of large liquid hydrogen bubble chambers for tracking the behavior of particles. Luis received the Nobel Prize in Physics in 1968 for his work in particle physics.

    That would seem to be a nice capstone to an illustrious career. But several years later his son Walter moved to Berkeley, where Luis had worked for many years, to join the university’s geology department. This gave father and son the chance to talk often about science. One day, Walter gave his dad a small polished cross-section of Gubbio K-T boundary rock and explained the mystery within it. Luis, then in his late 60s, was hooked and started thinking about how to help Walter crack it. They started brainstorming about how to measure the rates of change around the K-T boundary. They needed some kind of atomic timekeeper.

    Luis, obviously an expert on radioactivity and decay, first suggested that they measure the abundance of beryllium-10 (10Be) in the K-T clay. This isotope is constantly created in the atmosphere by the action of cosmic rays on oxygen. The more time the clay represented, the more 10Be would be present. Luis put Walter in touch with a physicist who knew how to do the measurements. But just as Walter was set to work, he learned that the published half-life of 10Be was wrong, The actual half-life was shorter, and too little 10Be would be left after 65 million years to measure it.

    Fortunately, Luis had another idea.

    Space Dust

    Luis remembered that meteorites are 10,000 times richer in elements from the platinum group than is the Earth’s crust. He figured that the rain of dust from outer space should be falling, on average, at a constant rate. Therefore, by measuring the amount of space dust (platinum elements) in rock samples, one could calculate how long they had taken to form.

    These elements are not abundant, but they are measurable. Walter figured that if the clay bed had been deposited over a few thousand years, it would contain a detectable amount of platinum group material, but if it had been deposited more quickly, it would be free of these elements.

    Luis decided that iridium, not platinum itself, was the best element to measure because it was more easily detected. He also knew the physicists to do the measurements, the two nuclear chemists Frank Asaro and Helen Michel at the Berkeley Radiation Laboratory.

    Walter gave Asaro a set of samples from across the Gubbio K-T boundary. For months he heard nothing back. The analytical techniques Asaro was using were slow, his equipment was not working, and he had other projects to work on.

    Nine months later Walter got a call from his dad. Asaro wanted to show them his results. They had expected iridium levels on the order 0.1 parts per billion (ppb) of sample. Asaro found 3 ppb of iridium in the portion of the clay bed, about 30 times more than expected and than the level found in other layers of the rock bed.

    Temp 6
    The iridium anomaly: The levels of iridium across the Gubbio formation are plotted. Note the spike in the K-T boundary clay.Data redrawn from Alvarez, et al. 1980 by Leanne Olds

    Why would that thin layer have so much iridium?

    Before they got too carried away with speculation, it was important to know if the high level of iridium was an anomaly of rocks around Gubbio, or a more widespread phenomenon. Walter went looking for another exposed K-T boundary site that they could sample. He found a place called Stevns Klint, south of Copenhagen, Denmark. Walter visited the clay bed there and could see right away that “something unpleasant had happened to the Danish sea bottom” when the clay was deposited. The cliff face was almost entirely made of white chalk, full of all kinds of fossils. But the thin K-T clay bed was black, stunk of sulfur, and had only fish bones in it. Walter deduced that during the time this “fish clay” was deposited, the sea was an oxygen-starved graveyard. He collected samples and delivered them to Frank Asaro.

    In the Danish fish clay, iridium levels were 160 times background levels.

    Walter suggested to Jan Smit that he also look for iridium in his clay samples. The Spanish clay also contained a spike of iridium. So did a sample taken from a K-T boundary in New Zealand, confirming that the phenomenon was global.

    Something very unusual, and very bad, had happened at the K-T boundary. The forams, the clay, the iridium, the dinosaurs were all signs—but of what?

    It Came From Outer Space

    The Alvarez’s concluded right away that the iridium must have been of extraterrestrial origin. They thought of a supernova, the explosion of a star that could shower earth with its elemental guts. The idea had been kicked around before in paleontological and astrophysics circles.

    Luis knew that heavy elements are produced in stellar explosions, so if that idea was right, there would be other elements besides iridium in unusual amounts in the boundary clay. The key isotope to measure was plutonium-244 with a half-life of 75 million years. It would be still present in the clay layer, but decayed in ordinary earth rocks. Rigorous testing proved there was no elevated level of plutonium. Everyone was at first disappointed, but the sleuthing continued.

    Luis kept thinking of some kind of scenario that could account for a worldwide die-off. He thought that maybe the solar system passed through a gas cloud, that the sun had become a nova, or that the iridium could have come from Jupiter. None of these ideas held up. An astronomy colleague at Berkeley, Chris McKee, suggested that an asteroid could have hit the earth. Luis at first thought that would only create a tidal wave, and he could not see how a giant tidal wave could kill the dinosaurs in Montana or Mongolia.

    Then he started to think about the volcanic explosion of the island of Krakatoa, in 1883. He recalled that miles of rock had been blasted into the atmosphere and that fine dust particles had circled the globe, and stayed aloft for two years or more. Luis also knew from nuclear bomb tests that radioactive material mixed rapidly between hemispheres. Maybe a large amount of dust from a large impact could turn day into night for a few years, cooling the planet and shutting down photosynthesis?

    If so, how big an asteroid would it have been?

    From the iridium measurements in the clay, the concentration of iridium in so-called chondritic meteorites and the surface area of the Earth, Luis calculated the mass of the asteroid to be about 300 billion metric tons. He then used various methods to infer that the asteroid had a diameter of 10 ± 4 kilometers (km).

    That diameter might not seem enormous with respect to the 13,000-km diameter of the Earth. But now consider the energy of the impact. Such an asteroid would enter the atmosphere traveling at about 25 km per second—over 50,000 miles per hour. It would punch a hole in the atmosphere 10 km across and hit the planet with the energy of 108 megatons of TNT. (The largest atomic bomb ever exploded released the equivalent of about one megaton—the asteroid was 100 million times more powerful.) With that energy, the impact crater would be about 200 km across and 40 km deep, and immense amounts of material would be ejected from the impact.

    The team had their foram- and dinosaur-killing scenario.

    Hell on Earth

    The asteroid crossed the atmosphere in about one second, heating the air in front of it to several times the temperature of the sun. On impact, the asteroid vaporized, an enormous fireball erupted out into space, and rock particles were launched as far as halfway to the moon. Huge shock waves passed through the bedrock, then curved back up to the surface and shot melted blobs and bedrock out to the edge of the atmosphere and beyond. A second fireball erupted from the pressure on the shocked limestone bedrock. For a radius of a few hundred kilometers or more from ground zero, life was annihilated. Further away, matter ejected into space fell back to earth at high speeds—like trillions of meteors—heated up on re-entry, heating the air and igniting fires. Tsunamis, landslides, and earthquakes further ripped apart landscapes nearer to the impact.

    Elsewhere in the world, death came a bit more slowly.

    The debris and soot in the atmosphere blocked out the sun, and the darkness may have lasted for months. This shut down photosynthesis and halted food chains at their base. Analysis of plant fossils and pollen grains indicate that half or more plant species disappeared in some locations. Animals at successively higher levels of the food chain succumbed. The K-T boundary marks more than the end of the dinosaurs, it is also the end of belemnites, ammonites, and marine reptiles. Paleontologists estimate that more than half of all the planet’s species went extinct. On land, nothing larger than 25 kilograms in body size survived.

    It was the end of the Mesozoic world.

    Where Is the Hole?

    Luis, Walter, Frank Asaro, and Helen Michel put together the whole story—the Gubbio forams, the iridium anomaly, the asteroid theory, the killing scenario—in a single paper published in the journal Science in June 1980.1 It is a remarkable, bold synthesis across different scientific fields, perhaps unmatched in scope by any other single paper in the modern scientific literature. Jan Smit and Jan Hertogen published their study based on Spanish rocks in the journal Nature, and reached a similar conclusion.2

    They were concerned, however, that the scientific community was not well prepared to accept the impact hypothesis. They had good reason to be worried. For the previous 150 years, since the beginning of modern geology, the emphasis had been on the power of gradual change. The science of geology had supplanted biblical stories of catastrophes. The idea of a catastrophic event on Earth was not just disturbing, it was considered unscientific. Until the asteroid impact papers, explanations for the disappearance of the dinosaurs usually invoked gradual changes in climate or in the food chain to which the animals could not adapt.

    Some geologists scoffed at the catastrophe scenario and some paleontologists were not at all persuaded by the asteroid theory. It was pointed out that the highest dinosaur bone in the fossil record at the time was 3 meters below the K-T boundary. Some suggested that perhaps the dinosaurs were already gone when the asteroid hit.3 Other paleontologists rebutted that dinosaur bones are so scarce, one should not expect to find them right up against the boundary.4 Rather, they argued the rich fossil record of forams and other creatures is the more revealing record, and forams and ammonites do persist right up to the K-T boundary.

    Of course, there was a somewhat larger problem that begged explanation: Where on Earth was that huge crater? To the skeptics and proponents this was an obvious weakness of the hypothesis, and so the hunt was on to find the impact zone, if it existed.

    At the time, there were only three known craters on Earth 100 km or more in size. None were the right age. If the asteroid had hit the ocean, which, after all, covers more than two-thirds of the planet’s surface, then searchers might be out of luck. The deep ocean was not well mapped, and a substantial part of the pre-Tertiary ocean floor has been swallowed up into the deep Earth in the continual movement of tectonic plates.

    In the decade following the proposal of the asteroid theory, many clues and trails were pursued, often to dead ends. As the failures mounted, Walter began to believe that the impact had in fact been in an ocean.

    Then a promising clue emerged from a riverbed in Texas. The Brazos River empties into the Gulf of Mexico. The sandy bed of the river is right at the K-T boundary. When examined closely by geologists familiar with the pattern of deposits left by tsunamis, the sandy bed was found to have features that could only be accounted for by a giant tsunami, perhaps more than 100 meters high. Moroever, mixed in with the tsunami debris were tektites—small bits of glassy rock that were ejected from the impact crater in molten form and cooled as they rained back down to Earth.5,6

    Temp 7
    Tektites: Tektites from Dogie Creek, Wyoming (top) and Beloc, Haiti (bottom). Note the bubbles within the glassy sphere—these formed in the vacuum of space as the particles were ejected out of the atmosphere.Top figure courtesy of Geological Society of Canada; bottom figure from Smit, J. [5]

    Many scientists were on the hunt for the impact site. Alan Hildebrand, a graduate student at the University of Arizona was one of the most tenacious. Alan concluded that the Brazos River tsunami bed was a crucial hint to the crater’s location—that it was in the Gulf of Mexico or the Caribbean. He looked at available maps to see if there might be any candidate craters around. He found some rounded features on maps of the sea floor north of Colombia. He also learned of some circular-shaped “gravity anomalies,” places where the concentration of mass varies, on the coast of Mexico’s Yucatan Peninsula.

    Alan searched for any other hints that he was on the right track. Alan noticed a report of tektites in late Cretaceous rocks from a site on Haiti. When he visited the lab that had made the report, he recognized the material as impact tektites. He then went to Haiti and discovered that the deposits there included very large tektites, along with shocked quartz grains—another signature of impacts. He and his advisor William Boynton surmised that the impact site was within 1,000 km of Haiti.

    When Hildebrand and Boynton presented their findings at a conference, they were contacted by Carlos Byars, a reporter for the Houston Chronicle. Byars told Hildebrand that geologists working for the state-owned Mexican oil company PEMEX might have discovered the crater many years earlier. Glen Penfield and Antonio Camargo had studied the circular gravity anomalies in the Yucatan. PEMEX would not allow them to release company data but they did suggest at a conference in 1981—just a year after the Alvarez’s asteroid proposal—that the feature they mapped might be the crater. Penfield had even written to Walter Alvarez with that suggestion.

    In 1991, Hildebrand, Boynton, Penfield, Camargo, and colleagues formally proposed that the 180-km-diameter crater (almost exactly the size predicted by the Alvarez team) one-half mile below the village of Chicxulub [Cheech-zhoo-loob] on the Yucatan Peninsula was the long-sought K-T impact crater.7,8

    Temp 8
    Location of Chicxulub crater and key impact evidence sites: The map shows locations of various impact evidence—the tsunami bed in the Brazos River, tektites in Haiti, the Ocean Drilling Site 1049, and the crater and surrounding ejected material on the Yucatan Peninsula. Leanne Olds

    There were still crucial tests to be done to determine if Chicxulub was truly the “smoking gun.” Another important issue was the age of the rock. This was no easy task to determine because the crater was buried. The best approach would be to test the core rock samples from the wells drilled by PEMEX in the region decades earlier. At first, it was feared that all of the core samples had been destroyed in a warehouse fire. They were eventually located and the rock that was melted by the impact could be dated by a number of laboratories. The results were spectacular. One lab obtained a figure of 64.98 + 0.05 million years, another a value of 65.2 + 0.4 million years. Right on the button—the melt rock was the same age as the K-T boundary.

    The Haitian tektites were also dated to this age, as was a deposit of material ejected from the impact. Detailed chemical analysis showed that the Chicxulub melt rock contained high levels of iridium9 and that it and the Haitian tektites came from the same source. Furthermore, the Haitian tektites had extremely low water content and the gas pressure inside was nearly zero, indicating that the glass solidified while in ballistic flight outside the atmosphere.

    Within a little more than a decade, what had at first seemed to be a radical and, to some, outlandish idea, had been supported by all sorts of indirect evidence, and then ultimately confirmed by direct evidence. Geologists subsequently identified ejected material that covers most of the Yucatan and is deposited at more than 100 K-T boundary sites around the world.10 We now understand that the history of life on Earth has not been the steady, gradual process envisioned by generations of geologists since Lyell and Darwin.

    The identification of the huge crater, while a great advance for the asteroid theory, was bittersweet for Walter. Luis Alvarez had passed away in 1988, just before its discovery.

    Temp 9
    K-T boundary sites: At left, a core sample, drilled at a site about 500km east of Florida (Ocean Drilling Project Site 1049), beautifully depicts the K-T event. Note the very large layer of ejected material on top of which the iridium-containing layer settled. On the right, an exquisitely well-preserved site near Tbilisi, Republic of Georgia, reveals a graded layer of spherules (smaller particles at the top, larger at the bottom) ejected from the impact that is also highly enriched in iridium (86 ppb). Left image courtesy of Integrated Ocean Drilling Program; right image from Smit, J. [5]

    One Punch or Two?

    The discovery of the K-T asteroid impact prompted extensive examination of whether other extinctions were due to impacts. It appears that none of the other four major extinctions of the past 500 million years is attributable to an impact. Yet, there have been many sizable asteroid or comet impacts on Earth over the same period, although none as large as the K-T strike. Since most impacts do not cause extinctions, and most extinctions are not due to impacts, the question has been raised of why the K-T asteroid was so devastating?

    Some scientists have suggested that where the asteroid struck was important. The target rock that was vaporized included a large amount of gypsum, which liberated a large amount of sulfur aerosols that could exacerbate the blockage of the sun, as well as produce acid rain that would alter bodies of water as well as soils. In addition, the impact liberated a large amount of chlorine sufficient to destroy today’s ozone layer.11

    But other evidence has accumulated that a period of massive volcanic eruptions might have weakened Earth’s ecosystems before the K-T impact. The so-called Deccan Traps in present-day western India have been shown to have poured massive amounts of carbon dioxide and sulfur dioxide into the atmosphere in episodic eruptions beginning several hundred thousand years prior to the K-T impact.12 Indeed, for many years, there has been an ongoing debate among some scientists as to whether the Deccan Traps or the K-T impact were the primary cause of the mass extinction. Because of the temporal coincidence between the K-T impact and the onset of the mass extinction, the consensus view has been that the K-T impact was the primary cause of extinction.13 Very recently, new geological evidence has suggested a scenario that may reconcile both viewpoints. It now appears that the largest Deccan eruptions occurred very close to the time of the impact.14,15 This has led some scientists to suggest that the seismic effect of the impact rocking the Earth’s mantle may have been sufficient to trigger enormous, climate-altering eruptions. In this scenario, the asteroid would be the first punch, and volcanism the knockout blow.

    Sean B. Carroll is a professor of molecular biology and genetics at the University of Wisconsin-Madison and Vice President for Science Education at the Howard Hughes Medical institute. His new book The Serengeti Rules will be published in March by Princeton University Press.


    1. Alvarez, L.W., Alvarez, W., Asaro, F., & Michel, H.V. Extraterrestrial cause for the Cretaceous-Tertiary extinction: Experimental results and theoretical interpretation. Science 208, 1095–1108 (1980).

    2. Smit, J. & Hertogen, J. An extraterrestrial event at the Cretaceous-Tertiary boundary. Nature 285, 198–200 (1980).

    3. Clemens, W.A., Archibald, J.D. & Hickey, L.J. Out with a whimper not a bang. Paleobiology 7, 293–98 (1981).

    4. Signor, P.W. & Lipps, J.H. Sampling bias, gradual extinction patterns and castastrophes in the fossil record. Geological Society of America Special Papers 190, 291–96 (1982).

    5. Smit, J. The global stratigraphy of the Cretaceous-Tertiary boundary impact ejecta. Annual Review of Earth and Planetary Sciences 27, 75–113 (1999).

    6. Simonson, B.M. & Glass, B.P. Spherule layers—Records of ancient impacts. Annual Review of Earth and Planetary Sciences 32, 329–361 (2004).

    7. Hildebrand, A.R., et al. Chicxulub crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico. Geology 19, 867–71 (1991).

    8. Pope, K.O., Ocampo, A.C., & Duller, C.E. Mexican site for K/T impact crater? Nature (Scientific Correspondence) 351, 105 (1991).

    9. Schuraytz, B.C., et al. Iridium metal in Chicxulub impact melt: Forensic chemistry on the K-T smoking gun. Science 271, 1573–1576 (1996).

    10. Claeys, P., Kiessling, W., & Alvarez, W. Distribution of Chicxulub ejecta at the Cretaceous-Tertiary Boundary. In Koeberl, C., & MacLeod, K.G., (Eds.) Catastrophic Events and Mass Extinctions: Impacts and Beyond Geological Society of America Special Paper, Boulder, CO (2002).

    11. Kring, D.A. The Chicxulub impact event and its environmental consequences at the Cretaceous-Tertiary boundary. Palaeogeography, Palaeoclimatology, Palaeoecology 255, 4-21 (2007).

    12. Schoene, B., et al. U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science 347, 182-184 (2015).

    13. Schulte, P., et al. The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary. Science 327, 1214–1218 (2010).

    14. Richards, M.A., et al. Triggering of the largest Deccan eruptions by the Chicxulub impact. Geological Society of America Bulletin (2015). Retrieved from doi: 10.1130/B31167.1

    15. Renne, P.R., et al. State shift in Deccan volcanism at the Cretaceous-Paleogene boundary, possibly induced by impact. Science 350, 76-78 (2015).

    See the full article here .

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