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

    From Nautilus: “The Day the Mesozoic Died” 

    Nautilus

    Nautilus

    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.

    References

    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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  • richardmitnick 4:08 pm on January 13, 2016 Permalink | Reply
    Tags: , Geology, , What is under the East Antarctic Ice Sheet   

    From GIZMODO: “There’s Something Enormous Buried Beneath the East Antarctic Ice Sheet” 

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    GIZMODO

    1.13.16
    Maddie Stone

    Temp 1

    Every week, we’re bombarded with images of dazzling terrains on Mars and Pluto, but there are still geologic wonders to be discovered right here on Earth. Case in point: a new study suggests there could be a canyon system more than twice as long as the Grand Canyon buried beneath an ice sheet in Antarctica. If confirmed, the frozen chasm would be the world’s longest by a wide margin.

    Faint traces of a ravine system stretching across the remote Princess Elizabeth Land in East Antarctica were first spotted by satellite images. A team of geologists then used radio-echo sounding, wherein radio waves are sent through the ice to map the shape of the rock beneath it. The results of this analysis, published recently in the journal Geology, reveal a chain of winding features over 600 miles long and half a mile deep buried beneath miles of ice.

    According to the researchers, the scarred landscape was probably carved out by liquid water long before the ice sheet grew. Satellite images also suggest that the canyon might be connected to a previously undiscovered subglacial lake, one that could cover up to 480 square miles.

    “It’s astonishing to think that such large features could have avoided detection for so long,” lead study author Steward Jamieson of Durham University said in a statement.

    Astonishing, yes—but not quite confirmed. We won’t know for sure that this canyon really exists until Jamieson’s preliminary results are verified by a comprehensive radio-echo sounding analysis of the entire landscape. That airborne survey is scheduled to take place later this year.

    If its existence is confirmed, the canyon system will become the world’s longest, handily stealing the title from Greenland’s Grand Canyon, which covers over 460 miles. Astonishingly, that canyon wasn’t discovered until 2013, when remote sensing data allowed scientists to peer through thick ice and reconstruct the rugged topography below. If one thing is clear from this recent spate of geologic finds, it’s that the age of discovery is far from over.

    Read the full scientific paper. at Geology.

    See the full article here .

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  • richardmitnick 6:02 pm on October 1, 2015 Permalink | Reply
    Tags: , , , Geology, , U Kansas   

    From Kansas: “Scientists refine hunt for Mars life by analyzing rock samples in Western U.S” 

    U Kansas bloc

    University of Kansas

    LAWRENCE — The search for life beyond Earth is one of the grandest endeavors in the history of humankind — a quest that could transform our understanding of our universe both scientifically and spiritually.

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    Petrographic thin section made from core sample. This 30 micron thin slice of rock allows a view of the types of features thought to be microbial. Here, the blue layers are an epoxy added in to see void-space in the rock, and the grey is sediment. The morphology of the orange-brown layers are suggestive of microbial activity, such as they way they roll over themselves in the bottom left and smoothly drape over the triangular feature. This type of deposition demonstrates that the sediment had to have a degree of cohesive stickiness, such as that provided by the presence of microbial mats.

    With news coming this week that NASA has confirmed the presence of flowing saltwater on the surface of Mars, the hunt for life on the Red Planet has new momentum.

    “One of the many reasons this is exciting is that life as we currently know it requires water,” said Alison Olcott-Marshall, assistant professor of geology at the University of Kansas. “So the fact that it’s present at Mars means that the most basic and universal requirement for life was fulfilled.”

    In the journal Astrobiology, Olcott-Marshall recently has published an analysis of Eocene rocks found in the Green River Formation, a lake system extending over parts of Colorado, Utah and Wyoming.

    Marshall and co-author Nicholas A. Cestari, a masters student in her lab, found these Green River rocks have features that visually indicate the presence of life, and they argue that probes to Mars should identify similar indicators on that planet and double-check them through chemical analysis.

    “Once something is launched into space, it becomes much harder to do tweaks — not impossible, but much, much harder,” Olcott-Marshall said. “Scientists are still debating the results of some of the life-detection experiments that flew to Mars on the Viking Missions in the late ’70s, in a large part because of how the experiments were designed. Looking at Earth-based analogs lets us get some of these bumps smoothed out here on Earth, when we can revise, replicate and re-run experiments easily.”

    2
    Petrographic thin section made from core sample. This 30 micron thin slice of rock allows a view of the types of features thought to be microbial, such as the layers that fold over themselves in the middle of the sample marked 2534.8’. This demonstrates that the sediment had to have a degree of cohesive stickiness, such as that provided by the presence of microbial mats.

    The researchers examined cored samples of rock from 50 million years ago that included sections of “microbial mats.”

    “Microbial mats are essentially the microbial world’s version of apartment buildings — they are layered communities of microbes, and each layer represents a different metabolic strategy,” Olcott-Marshall said. “Generally, the photosynthetic microbes are at the top, and then every successive layer makes use of the waste products of the level above. Thus, not only does a microbial mat contain a great deal of biology, but a great number of chemicals, pigments and metabolic products are made, which means lots of potential biosignatures.”

    At times during the Eocene, the Green River Formation’s water chemistry purged fish and other organisms from the lake, providing room for these microbes to thrive.

    “During these times, ‘microbialites’ formed — these are rocks thought to be made by microbial processes, essentially the preserved remnants of microbial mats. The Green River Formation has a wide variety of these structures, and these features are why we went looking in these rocks, as microbialites are one life-detection target on Mars.”

    First, the researchers visually inspected the cored samples for signs of biology by identifying geological signs associated with microbialites — such as “stromatolites.”

    “These are things like finely laminated sediments, where each lamination follows the ones below, or signs of cohesive sediment, things like layers that roll over onto themselves or are at an angle steeper than what gravity would allow,” Olcott-Marshall said. “These are all thought to be signs that microbes are helping hold sediment together.”

    If visual examination pointed to the presence of biology in sections of the rock cores, the researchers looked to confirm the presence of life. They powdered those rock samples in a ball mill, and then used hot organic solvents like methanol to remove any organic carbons that might have been preserved in the rocks. That solvent was then concentrated and analyzed with gas chromatography/mass spectroscopy.

    “GC/MS allows an identification of compounds, including organic molecules, preserved in a rock,” Olcott-Marshall said. “Viking was the first time that a GC/MS was sent to Mars, and there is one up there right now on Curiosity collecting data.”

    NASA Viking 2
    NASA/Viking 2

    NASA Mars Curiosity Rover
    NASA/Mars Curiosity Rover

    Through GC/MS, the researchers determined that rock structures appearing to be biological indeed hosted living organisms millions of years ago: analysis showed the presence of lipid biomarkers.

    “A lipid biomarker is the preserved remnant of a lipid, or a fat, once synthesized by an organism,” Olcott-Marshall said. “These can be simple or very complex. Different organisms make different lipids, so identifying the biomarker can often allow a deeper understanding of the biota or the environment present when a rock was formed. These are a type of biosignature.”

    The researchers said their results could be a powerful guide for sample selection on Mars.

    “There is a GC/MS on Curiosity right now, but there are only nine sample cups dedicated for looking for biomarkers like these,” Olcott-Marshall said. “It’s crucial those nine samples are ones most likely to guarantee success. Additionally, one of the goals of the planned 2020 rover mission is to identify samples for caching for eventual return to Earth. The amount of sample that can be returned is likely very small, thus, once again, doing our best to guarantee success is very important. What this shows is that we can use visual inspection to help us screen for these samples that are likely to be successful for further biosignature analysis.”

    She said microbial and non-microbial rocks are found in similar environments, with identical preservation histories for millions of years, and many of the same chemical parameters, such as amounts of organic carbon preserved in the rocks.

    “The only difference is that one rock is shaped in a way people have associated with biology, and sure enough, those rocks are the ones that seem to preserve the biosignatures, at least in the Green River,” she said.

    See the full article here.

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    U Kansas campus

    Since its founding, the University of Kansas has embodied the aspirations and determination of the abolitionists who settled on the curve of the Kaw River in August 1854. Their first goal was to ensure that the new Kansas Territory entered the union as a free state. Another was to establish a university.

    Nearly 150 years later, KU has become a major public research and teaching institution of 28,000 students and 2,600 faculty on five campuses (Lawrence, Kansas City, Overland Park, Wichita, and Salina). Its diverse elements are united by their mission to educate leaders, build healthy communities, and make discoveries that change the world.

    A member of the prestigious Association of American Universities since 1909, KU consistently earns high rankings for its academic programs. Its faculty and students are supported and strengthened by endowment assets of more than $1.44 billion. It is committed to expanding innovative research and commercialization programs.

    KU has 13 schools, including the only schools of pharmacy and medicine in the state, and offers more than 360 degree programs. Particularly strong are special education, city management, speech-language pathology, rural medicine, clinical child psychology, nursing, occupational therapy, and social welfare. Students, split almost equally between women and men, come from all 50 states and 105 countries and are about 15 percent multicultural. The University Honors Program is nationally recognized, and KU has produced 26 Rhodes Scholars, more than all other Kansas schools combined.

     
  • richardmitnick 7:20 am on August 10, 2015 Permalink | Reply
    Tags: , , , Geology   

    From Cosmos: “Earth’s early magnetic field locked in 4.2 billion-year-old crystals” 

    Cosmos Magazine bloc

    COSMOS

    10 Aug 2015
    Belinda Smith

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    An artist’s depiction of Earth’s magnetic field deflecting high-energy protons from the Sun four billion years ago (not to scale).Credit: Michael Osadciw / University of Rochester.

    Like tiny compasses frozen in time, ancient zircon gems from Western Australia have shown Earth’s magnetic field is at least four billion years old – more than 700 million years older than previous evidence suggested. Because the magnetic field protects the Earth’s atmosphere from destructive solar rays, it raises the possibility that life could have made its debut much earlier than previously thought.

    A North American team, led by John Tarduno at New York’s University of Rochester, found the young Earth had a chaotic magnetic field that was, at times, as strong as our field today. They reported their work in Science in July.

    It’s “astonishing to be able to probe the magnetic field that far back”, says Louis Moresi, a geoscientist at the University of Melbourne.

    Earth formed some 4.5 billion years ago, accreting from dust and proto-planetary fragments swirling around the Sun. Even in the near absolute zero temperatures of space, enough heat was trapped in the colliding mass to melt material in its core. Over time, the radioactive decay of uranium and other ‘hot’ elements has kept the core molten.

    Today, if you were to drill through the crust, you’d travel through 2,900 kilometres of rocky mantle before reaching the outer core. You’d then slither through 2,200 kilometres of liquid iron, before hitting a metallic inner core about 1,200 kilometres in diameter – a little smaller than the Moon. The inner core is kept solid by the enormous pressures at the centre of the Earth.

    It’s the liquid outer core, constantly stirred by convection currents, that generates our magnetic field. Just as hot air rises, hot iron rises towards Earth’s cooler surface, carrying heat that escapes through the mantle and crust. As the iron cools, it sinks, providing a constant stirring motion that generates our magnetic field.

    The mantle layer is vital to maintaining this motion. If it is too thin, the heat in the core dissipates quickly, along with the magnetic field. If it is too insulating, the vital convection currents shut down.

    Thanks to the Earth’s daily rotation and the stabilising solid inner core, the convection currents in the molten outer core have settled into spiralling columns that lie parallel to the Earth’s axis, giving us the elegant north-south dipole our compasses use today. What was it like in the Earth’s youth?

    It’s hard to say. Our dynamic planet’s surface is continually crushed, stretched and recycled – thanks to plate tectonics – and rock remnants from the Earth’s earliest days are scarce.

    3
    The tectonic plates of the world were mapped in the second half of the 20th century.

    But thanks to a zircon crystal dug out of 4.4-billion-year-old sandstone on a Western Australian sheep ranch, we may have a clue. The University of Wisconsin-Madison-led study last year claimed the gemstone was born 100 million years after the Earth itself.

    For Tarduno and his team, that report raised an exciting possibility. They realised that like mosquitoes in amber, tiny iron oxide grains also known as magnetite would be trapped inside the zircon as it solidified and could have recorded the ancient magnetic field. His team returned to the same area and collected 25 zircon crystals dated from 3.3 to 4.2 billion years old, and examined them for microscopic magnetite flakes. But a super-sensitive instrument was needed to pick out the magnetic alignment in the grains.

    Enter the superconducting quantum interference device (the SQUID).
    SQUID

    SQUID superconducting quantum interference device

    This ultra-high-definition magnetometer can detect faint magnetic fields – as much as 100 billion times weaker than the energy needed to move a compass needle. The SQUID found the magnetite grains harboured magnetic fields of varying strengths – from the equivalent of today’s magnetic field, to 12% of its strength.

    2
    A 4.4 billion-year-old zircon crystal from the Jack Hills region of Western Australia, which is the oldest bit of the Earth’s crust.Credit: John Valley

    Before this study, the oldest evidence for a magnetic field on Earth came from South African rocks dated at 3.2 and 3.45 billion years old. Two of the oldest zircons in Tarduno’s study were 750 million years older. “It’s amazing what they could get out of these little guys,” Moresi says, adding they really are “miracle crystals”.

    So why does the age of the magnetic field affect life’s appearance on Earth?

    Basically, the field shields us from our life-giver – the Sun. Streams of charged particles flow from the Sun, bombarding the inner planets and stripping away their water and atmosphere – unless a magnetic field is strong enough to deflect the onslaught.

    Tarduno points to our neighbour, Mars. The barren world once had a magnetic field, but no longer – nor any surface liquid water or atmosphere to speak of. Scientists think that around four billion years ago the Earth and Mars were battered by asteroids. On Mars, the onslaught over-heated its mantle. As the heat gradient between the core and mantle was lost, its core’s convection currents slowed and eventually stopped, switching off its magnetic shield and allowing the solar wind to whisk its atmosphere away. “It may also be a major reason why Mars was unable to sustain life,” he says.

    But the Earth was a little larger, and able to weather the storm. Ensconced in its protective magnetic bubble, life could begin to flourish.

    See the full article here.

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  • richardmitnick 1:53 pm on July 29, 2015 Permalink | Reply
    Tags: , , Geology   

    From ASU Via KJZZ: “Debate Continues Over Age Of The Grand Canyon” 

    ASU Bloc

    ASU

    KJZZ
    1

    July 27, 2015
    Melissa Sevigny

    1
    A view from the South Rim of the Grand Canyon. (Photo by Melissa Sevigny – KNAU)

    New research supports the long-held hypothesis that the Grand Canyon is as young as 6 million years. That’s what geologists originally believed before a different study claimed it was tens of millions of years older.

    The study, which was conducted by geologists at Arizona State University, compares the western Grand Canyon with the Grand Wash Cliffs. It found that the canyon is steeper than the cliffs, which suggests erosion started more recently.

    “So our conclusion is that it’s younger than the activity on the Grand Wash Fault,” said Andrew Darling, lead author of the study. “If the canyon’s younger than the fault, that would be consistent with the 6 million year old canyon age.”

    A previous study in 2012 revitalized research and debate when it claimed the Grand Canyon might be as old as 70 million years. That study looked at the decay of radioactive elements in rocks. The ASU study looked at geomorphology, particularly erosion rates.

    See the full article here.

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    ASU is the largest public university by enrollment in the United States.[11] Founded in 1885 as the Territorial Normal School at Tempe, the school underwent a series of changes in name and curriculum. In 1945 it was placed under control of the Arizona Board of Regents and was renamed Arizona State College.[12][13][14] A 1958 statewide ballot measure gave the university its present name.
    ASU is classified as a research university with very high research activity (RU/VH) by the Carnegie Classification of Institutions of Higher Education, one of 78 U.S. public universities with that designation. Since 2005 ASU has been ranked among the Top 50 research universities, public and private, in the U.S. based on research output, innovation, development, research expenditures, number of awarded patents and awarded research grant proposals. The Center for Measuring University Performance currently ranks ASU 31st among top U.S. public research universities.[15]

    ASU awards bachelor’s, master’s and doctoral degrees in 16 colleges and schools on five locations: the original Tempe campus, the West campus in northwest Phoenix, the Polytechnic campus in eastern Mesa, the Downtown Phoenix campus and the Colleges at Lake Havasu City. ASU’s “Online campus” offers 41 undergraduate degrees, 37 graduate degrees and 14 graduate or undergraduate certificates, earning ASU a Top 10 rating for Best Online Programs.[16] ASU also offers international academic program partnerships in Mexico, Europe and China. ASU is accredited as a single institution by The Higher Learning Commission.

    ASU Tempe Campus
    ASU Tempe Campus

     
  • richardmitnick 9:36 am on July 23, 2015 Permalink | Reply
    Tags: , Geology,   

    From OSU: “Satellites peer into rock 50 miles beneath Tibetan Plateau” 

    OSU

    Ohio State University

    July 21, 2015
    Pam Frost Gorder

    1
    Topography (left) and a shaded relief map (right) of the rock deep beneath the Tibetan Plateau. Color indicates kilometers below Earth’s surface. Image by Younghong Shin of the Korea Institute of Geosciences and Mineral Resource, courtesy of The Ohio State University.

    Gravity data captured by satellite has allowed researchers to take a closer look at the geology deep beneath the Tibetan Plateau.

    The analysis, published in the journal Nature Scientific Reports, offers some of the clearest views ever obtained of rock moving up to 50 miles below the plateau, in the lowest layer of Earth’s crust.

    There, the Indian tectonic plate presses continually northward into the Eurasian tectonic plate, giving rise to the highest mountains on Earth—and deadly earthquakes, such as the one that killed more than 9,000 people in Nepal earlier this year.

    The study supports what researchers have long suspected: Horizontal compression between the two continental plates is the dominant driver of geophysical processes in the region, said C.K. Shum, professor and Distinguished University Scholar in the Division of Geodetic Science, School of Earth Sciences at The Ohio State University and a co-author of the study.

    “The new gravity data onboard the joint NASA-German Aerospace Center GRACE gravimeter mission and the European Space Agency’s GOCE gravity gradiometer missionenabled scientists to build global gravity field models with unprecedented accuracy and resolution, which improved our understanding of the crustal structure,” Shum said. “Specifically, we’re now able to better quantify the thickening and buckling of the crust beneath the Tibetan Plateau.”

    NASA Grace
    NASA/Grace

    ESA GOCE Spacecraft
    ESA/GOCE

    Younghong Shin

    Shum is part of an international research team led by Younghong Shin of the Korea Institute of Geosciences and Mineral Resource. With other researchers in Korea, Italy and China, they are working together to conduct geophysical interpretations of the Tibetan Plateau geodynamics using the latest combined gravity measurements by the GOCE gravity gradiometer and the GRACE gravimeter missions.

    Satellites such as GRACE and GOCE measure small changes in the force of gravity around the planet. Gravity varies slightly from place to place in part because of an uneven distribution of rock in Earth’s interior.

    The resulting computer model offers a 3-D reconstruction of what’s happening deep within the earth.

    As the two continental plates press together horizontally, the crust piles up. Like traffic backing up on a congested freeway system, the rock follows whatever side roads may be available to relieve the pressure.

    But unlike cars on a freeway, the rock beneath Tibet has two additional options for escape. It can push upward to form the Himalayan mountain chain, or downward to form the base of the Tibetan Plateau.

    The process takes millions of years, but caught in the 3-D image of the computer model, the up-and-down and side-to-side motions create a complex interplay of wavy patterns at the boundary between the crust and the mantle, known to researchers as the Mohorovičić discontinuity, or “Moho.”

    “What’s particularly useful about the new gravity model is that it reveals the Moho topography is not random, but rather has a semi-regular pattern of ranges and folds, and agrees with the ongoing tectonic collision and current crustal movement measured by GPS,” Shin said.

    As such, the researchers hope that the model will provide new insights into the analysis of collisional boundaries around the world.

    Co-author Carla Braitenberg of the University of Trieste said that the study has already helped explain one curious aspect of the region’s geology: the sideways motion of the Tibetan Plateau. While India is pushing the plateau northward, GPS measurements show that portions of the crust are flowing eastward and even turning to the southeast.

    “The GOCE data show that the movement recorded at the surface has a deep counterpart at the base of the crust,” Braitenberg said. Connecting the rock flow below to movement above will help researchers better understand the forces at work in the region.

    Those same forces led to the deadly Nepal earthquake in April 2015. But Shum said that the new model almost certainly won’t help with earthquake forecasting—at least not in the near future.

    “I would say that we would understand the mechanism more if we had more measurements,” he said, but such capabilities “would be very far away.”

    Even in California—where, Shum pointed out, different tectonic processes are at work than in Tibet—researchers are unable to forecast earthquakes, despite having abundant GPS, seismic and gravity data. Even less is known about Tibet, in part because the rough terrain makes installing GPS equipment difficult.

    Other co-authors on the study included Sang Mook Lee of Seoul National University; Sung-Ho Na of the University of Science and Technology in Daejeon, Korea;

    Kwang Sun Choi of Pusan National University; Houtse Hsu of the Institute of Geodesy & Geophysics, Chinese Academy of Sciences; and Young-Sue Park and Mutaek Lim of the Korea Institute of Geosciences and Mineral Resource.

    This research was supported by the Basic Research Project of the Korea Institute of Geoscience and Mineral Resources, funded by the Ministry of Science, ICT and Future Planning of Korea. Shum was partially supported by NASA’s GRACE Science Team Program and Concept in Advanced Geodesy Program. Braitenberg was partially supported by the European Space Agency’s Center for Earth Observation as part of the GOCE User ToolBox project.

    See the full article here.

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  • richardmitnick 8:20 am on June 5, 2015 Permalink | Reply
    Tags: , , Geology,   

    From Michigan Tech: “Clues to the Earth’s Ancient Core” 

    Michigan Tech bloc

    Michigan Technical University

    June 4, 2015
    Allison Mills

    1
    Aleksey Smirnov drills into an outcrop in Australia’s Widgiemooltha dike swarm.

    Old rocks hold on to their secrets. Now, a geophysicist at Michigan Technological University has unlocked clues trapped in the magnetic signatures of mineral grains in those rocks.. These clues will help clear up the murky history of the Earth’s early core.

    The journal Earth and Planetary Science Letters published a paper on the subject earlier this year. Aleksey Smirnov, an associate professor of geophysics and adjunct associate professor of physics at Michigan Tech, led the study. The work is a part of a large research program led by Smirnov and supported by the National Science Foundation (NSF), including his CAREER Award, a prestigious NSF grant. Through this work, he has traveled the world seeking rocks that provide insight into the ancient earth’s core.

    Earth’s Ancient Geodynamo

    The magnetic field comes from the earth’s core: The solid inner core, made of iron, spins and powers convective currents in the liquid outer core. Those currents create the magnetic field, and the system is called the geodynamo.

    “At any point, the field can be described by its direction and strength,” Smirnov says, adding that the modern magnetic field is weaker than that of a refrigerator magnet and that intensity has changed throughout geologic time. “What we call paleointensity in our paper refers to the field’s strength,” he explains.

    Smirnov and his co-author, David Evans of Yale University, examined the paleointensity measurements of rocks more than two billion years old. Rocks that old record a magnetic field from a rather mysterious geodynamo.

    That’s because the core didn’t always have a solid center — it used to be all liquid. And being liquid would make for a weak, chaotic magnetic field.

    “What happened at some point, because the earth is constantly cooling, the center formed a small, solid inner core,” Smirnov says. “But this event is uncertain in terms of timing.”

    A number of models analyze what this timing could have been, but they estimate any time between half a billion years ago and three billion years ago — which is like saying an adolescent will hit puberty sometime between ages 8 to 30. To better pinpoint the timing of the inner core’s formation, Smirnov scours the world for old Precambrian rocks.

    Magnetic Records in Rocks

    Smirnov focuses on rocks that are not just old, but magnetic, and he tests the samples in the Earth Magnetism Lab at Michigan Tech. Within the lab is a room, built above the concrete floor and boxed in with a special steel alloy — it’s a metal-free zone. Inside the room, Smirnov uses a magnetometer: a device that measures magnetic properties in rocks and, more specifically, their iron-rich minerals.

    2

    Magnetite is an iron oxide with magnetic properties, and when it crystallizes in a rock, it records the strength and orientation of the earth’s magnetic field. Some rocks record this better than others; an ideal rock cools fast and is well-preserved.

    “Because of the rarity of well-preserved extrusive Precambrian rocks,” Smirnov writes in his paper, “relatively quickly cooled shallow intrusions such as mafic dikes and sills represent an attractive alternative target for paleointensity studies.”

    The rocks Smirnov and his team sampled in Australia’s Widgiemooltha dike swarm are the best available, considering the cluster of intrusive rock formations has been eroded, buried and baked over the past two billion years. The dike swarm is important because the Widgiemooltha rocks, collected from 24 different field sites, contain key magnetite grains. After some time in the lab’s magnetometer, the minerals begin to reveal their long-held magnetic secrets.

    Basal Mantle Ocean and Beyond

    Given the rocks’ age and the chaotic nature of the early magnetic field, Smirnov predicted the paleointensity recorded in the magnetite grains would be weak. However, he and his team found the paleointensity readings were relatively strong.

    “This contradicts the models that show a young solid inner core — and right now, that’s a mystery,” Smirnov says. Although, he adds, there is a new theory that is consistent with this data.

    In the basal mantle ocean theory, the boundary between the solid mantle — the bulk of earth’s interior — and the early earth’s core could have been swaddled in a dense layer of partially melted rock. The difference in composition and density could have been enough to jumpstart a stronger magnetic field.

    Delving deeper into the core’s evolution has significance beyond the earth’s interior, too. The magnetic field helps protect life on earth from cosmic radiation. Understanding the ancient geodynamo could also expand our knowledge of earth’s earliest life. Smirnov plans to study that connection — and more exceptionally old rocks — in the next leg of his research.

    See the full article here.

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    Michigan Tech Campus
    Michigan Technological University (http://www.mtu.edu) is a leading public research university developing new technologies and preparing students to create the future for a prosperous and sustainable world. Michigan Tech offers more than 130 undergraduate and graduate degree programs in engineering; forest resources; computing; technology; business; economics; natural, physical and environmental sciences; arts; humanities; and social sciences.
    The College of Sciences and Arts (CSA) fills one of the most important roles on the Michigan Tech campus. We play a part in the education of every student who comes through our doors. We take pride in offering essential foundational courses in the natural sciences and mathematics, as well as the social sciences and humanities—courses that underpin every major on campus. With twelve departments, 28 majors, 30-or-so specializations, and more than 50 minors, CSA has carefully developed programs to suit many interests and skill sets. From sound design and audio technology to actuarial science, applied cognitive science and human factors to rhetoric and technical communication, the college offers many unique programs.

     
  • richardmitnick 1:21 pm on April 6, 2015 Permalink | Reply
    Tags: , Geology, , Sinkholes   

    From livescience: “Why Dangerous Sinkholes Keep Appearing Along the Dead Sea” 

    Livescience

    April 06, 2015
    Tanya Lewis

    1
    Credit: Eli Raz

    For millennia, the salty, mineral-rich waters of the Dead Sea have drawn visitors and health pilgrims to its shores. But in recent years, gaping chasms have been opening up without warning along its banks, posing a threat to such visitors and tourism in general.

    4
    Satellite photograph showing the location of the Dead Sea

    Nestled between Israel and the Palestinian territories to the west, and Jordan to the east, the Dead Sea is famous for is extreme salinity (34 percent salt, almost 10 times as salty as the ocean), and for having the lowest elevation on Earth, at 1,407 feet (429 meters) below sea level.

    But for the past few decades, the sea has been shrinking rapidly, due to the diversion of water from the Jordan River (which feeds the Dead Sea) and mineral mining from its waters in the south. The water’s surface is currently receding by about 3 feet (1 m) per year, according to Hanan Ginat, a geologist and academic chairman of the Dead Sea and Arava Research Center, in Israel.

    2
    For the past few decades, the sea has been receding by about 3 feet (1m) per year, due to the diversion of water from the Jordan River (which feeds the Dead Sea) and mineral mining from its waters in the south. As the briny water recedes, fresh groundwater wells up and dissolves layers of salt, creating large underground cavities, above which sinkholes form. (Image credit: Eli Raz)

    3
    Geologist Eli Raz of Israel’s Dead Sea and Arava Research Center has studied the sinkhole problem in depth. Raz found that many of the craters developed along seismic fault lines in the Jordan Rift Valley. Inside these faults, the dissolved salts are less stable and more susceptible to invading freshwater, which hollows out the gaping holes, Raz’s studies suggest. (Image credit: Eli Raz)

    As the briny water recedes, fresh groundwater wells up and dissolves layers of salt, creating large underground cavities, above which sinkholes form. The holes can open up without warning, Ginat told Live Science. “We’re looking for systems to forecast where they will happen, but it’s very complicated,” he added.

    The main reason for the Dead Sea’s decline is diversion of water from the Jordan River, which used to provide about 450 billion gallons (1.7 billion cubic meters), but now only provides about 20 percent of that, Ginat said. A factory called Dead Sea Works, which pumps out seawater to harvest its salts and minerals, plays a role in the problem, he said.

    Ginat’s colleague at Dead Sea and Arava Research Center, geologist Eli Raz, has studied the sinkhole problem in depth. Raz found that many of the craters developed along seismic fault lines in the Jordan Rift Valley. Inside these faults, the dissolved salts are less stable and more susceptible to invading freshwater, which hollows out the gaping holes, Raz’s studies suggest.

    The sinkholes were first noticed in the 1970s, but have been forming more rapidly in recent years. The holes are dangerous for people who visit or live in the area, and while no one has been killed, the problem should be taken seriously, researchers warn. The sinkholes can reach up to 82 feet (25 m) deep and 131 feet (40 m) in diameter, and nearby holes sometimes join to form giant ones, according to Raz and his colleagues. More than 4,000 sinkholes exist today, mostly on the sea’s western shores, Ginat said.

    However, there may be a way to stave off the Dead Sea’s decline. Authorities have proposed a canal that would run from the Red Sea to the Dead Sea, called the Red Sea-Dead Sea Conduit, which, in addition to providing water to Jordan, Israel and the Palestinian territories, would bring salt water to the Dead Sea and generate electricity to supply its own energy. Israel and Jordan approved the first stage of the project last month, Ginat said.

    “You can’t stop the sinkholes,” Ginat said. But when people plan roads, buildings and other infrastructure, they should take note of the research, “and choose where to put things [based on] the knowledge we have about the sinkholes,” he said.

    Other areas of the world are also home to puzzling sinkholes. For instance, in Siberia, at least seven giant craters have been found since 2014, which scientists believe to be the result of the explosive release of methane gas from melting permafrost. Researchers have called for urgent investigation of the craters out of safety concerns.

    See the full article here.

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  • richardmitnick 9:32 am on January 14, 2015 Permalink | Reply
    Tags: , , Geology   

    From astrobio.net: “Rare Mineral found in a Wisconsin Crater” 

    Astrobiology Magazine

    Astrobiology Magazine

    Jan 14, 2015
    Aaron L. Gronstal

    1
    With support from the NASA Astrobiology Program, Cavosie brought students from the University of Puerto Rico to study outcrops at the Rock Elm meteorite impact structure. Reidite was found in the samples they collected. Credit: Aaron Cavosie

    Scientists have discovered one of the rarest minerals on Earth in a Wisconsin impact crater.

    Aaron Cavosie of the University of Puerto Rico, and member of the NASA Astrobiology Institute Team at the University of Wisconsin, brought students to an impact site in Rock Elm, Wisconsin to collect samples. In those samples, Cavosie and colleagues discovered the mineral reidite, making Rock Elm the fourth site on Earth where the mineral has been found in nature.

    Reidite is created at high pressures and was first identified in the laboratory in the 1960s. The conditions in which reidite forms have been well-constrained by experiments in the lab but, prior to Rock Elm, it was only found naturally in the Chesapeake Bay Impact Structure (Virginia), the Ries Crater (Germany), and the Xiuyan Crater (China).

    The Rock Elm structure is 6.5 kilometers in diameter and was formed during the Middle Ordovician. This means that the reidite found at Rock Elm is at least 450 million years old, making it the oldest preserved reidite yet discovered.

    Another important aspect of the research is that the reidite was found in sandstone – the first time the mineral was spotted in this type of rock. There are many other impact structures that have been formed in sandstone, and its possible that a re-examination of these sites could reveal more reidite.

    “I get the sense that, because reidite had never been found in this kind of rock, if something’s never found there, your not going to go look for it purposefully,” said Cavosie in an interview with Wisconsin Public Radio. “Now that we’ve identified this recorder of even far more extreme impact conditions than what was known previously at Rock Elm, that tool can be applied to many, many other localities to try to recreate the impact conditions and better understand the effects on the surface environments of some of these impacts.”

    Wisconsin Public Radio produced an interview with Aaron Cavosie and Bill Cordua of UW-River Falls, who discovered the Rock Elm disturbance. To listen to the show, visit: http://www.wpr.org/listen/682916

    The initial findings were presented at the 2014 GSA Annual Meeting in Vancouver.

    See the full article here.

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  • richardmitnick 10:00 pm on January 2, 2015 Permalink | Reply
    Tags: , Geology, , ,   

    From U Chicago: “Modern genetics confirm ancient relationship between fins and hands” 

    U Chicago bloc

    University of Chicago

    December 29, 2014
    John Easton

    Paleontologists have documented the evolutionary adaptations necessary for ancient lobe-finned fish to transform pectoral fins used underwater into strong, bony structures, such as those of Tiktaalik roseae. This enabled these emerging tetrapods, animals with limbs, to crawl in shallow water or on land. But evolutionary biologists have wondered why the modern structure called the autopod—comprising wrists and fingers or ankles and toes—has no obvious morphological counterpart in the fins of living fishes.

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    Tiktaalik

    In the Dec. 22, 2014, issue of the Proceedings of the National Academy of Sciences, researchers argue previous efforts to connect fin and fingers fell short because they focused on the wrong fish. Instead, they found the rudimentary genetic machinery for mammalian autopod assembly in a non-model fish, the spotted gar, whose genome was recently sequenced.

    “Fossils show that the wrist and digits clearly have an aquatic origin,” said Neil Shubin, the Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy and a leader of the team that discovered Tiktaalik in 2004. “But fins and limbs have different purposes. They have evolved in different directions since they diverged. We wanted to explore, and better understand, their connections by adding genetic and molecular data to what we already know from the fossil record.”

    Initial attempts to confirm the link based on shape comparisons of fin and limb bones were unsuccessful. The autopod differs from most fins. The wrist is composed of a series of small nodular bones, followed by longer thin bones that make up the digits. The bones of living fish fins look much different, with a set of longer bones ending in small circular bones called radials.

    The primary genes that shape the bones, known as the HoxD and HoxA clusters, also differ. The researchers first tested the ability of genetic “switches” that control HoxD and HoxA genes from teleosts—bony, ray-finned fish—to shape the limbs of developing transgenic mice. The fish control switches, however, did not trigger any activity in the autopod.

    Teleost fish—a vast group that includes almost all of the world’s important sport and commercial fish—are widely studied. But researchers began to realize they were not the ideal comparison for studies of how ancient genes were regulated. When they searched for wrist and digit-building genetic switches, they found “a lack of sequence conservation” in teleost species.

    They traced the problem to a radical change in the genetics of teleost fish. More than 300 million years ago, after the fish-like creatures that would become tetrapods split off from other bony fish, a common ancestor of the teleost lineage went through a whole-genome duplication—a phenomenon that has occurred multiple times in evolution.

    By doubling the entire genetic repertoire of teleost fish, this WGD provided them with enormous diversification potential. This may have helped teleosts to adapt, over time, to a variety of environments worldwide. In the process, “the genetic switches that control autopod-building genes were able to drift and shuffle, allowing them to change some of their function, as well as making them harder to identify in comparisons to other animals, such as mice,” said Andrew Gehrke, a graduate student in the Shubin Lab and lead author of the study.

    Not all bony fishes went through the whole genome duplication, however. The spotted gar, a primitive freshwater fish native to North America, split off from teleost fishes before the WGD.

    When the research team compared Hox gene switches from the spotted gar with tetrapods, they found “an unprecedented and previously undescribed level of deep conservation of the vertebrate autopod regulatory apparatus.” This suggests, they note, a high degree of similarity between “distal radials of bony fish and the autopod of tetrapods.”

    They tested this by inserting gar gene switches related to fin development into developing mice. This evoked patterns of activity that were “nearly indistinguishable,” the authors note, from those driven by the mouse genome.

    “Overall,” the researchers conclude, “our results provide regulatory support for an ancient origin of the ‘late’ phase of Hox expression that is responsible for building the autopod.”

    This study was supported by the Brinson Foundation, the National Science Foundation, the Brazilian National Council for Scientific and Technological Development grants, the National Institutes of Health, the Volkswagen Foundation in Germany, the Alexander von Humboldt-Foundation, the Spanish and Andalusian governments, and Proyecto de Excelencia.

    Additional authors include Mayuri Chandran and Tetsuya Nakamura from the University of Chicago; Igor Schneider from the Instituto de Ciencias Biologicas, Universida de Federal do Para, Belem, Brazil; Elisa de la Calle-Mustienes, Juan J. Tena, Carlos Gomez-Marin and José Luis Gómez-Skarmeta from the Centro Andaluz de Biología del Desarrollo, Sevilla, Spain; and Ingo Braasch and John H. Postlethwait from the Institute of Neuroscience, University of Oregon.

    See the full article here.

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    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

     
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