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  • richardmitnick 12:07 pm on December 22, 2016 Permalink | Reply
    Tags: , Explorers Find Passage to Earth’s Dark Age, Geology,   

    From Quanta: “Explorers Find Passage to Earth’s Dark Age” 

    Quanta Magazine
    Quanta Magazine

    December 22, 2016
    Natalie Wolchover

    1
    Earth scientists hope that their growing knowledge of the planet’s early history will shed light on poorly understood features seen today, from continents to geysers. Eric King

    Geochemical signals from deep inside Earth are beginning to shed light on the planet’s first 50 million years, a formative period long viewed as inaccessible to science.

    In August, the geologist Matt Jackson left California with his wife and 4-year-old daughter for the fjords of northwest Iceland, where they camped as he roamed the outcrops and scree slopes by day in search of little olive-green stones called olivine.

    A sunny young professor at the University of California, Santa Barbara, with a uniform of pearl-snap shirts and well-utilized cargo shorts, Jackson knew all the best hunting grounds, having first explored the Icelandic fjords two years ago. Following sketchy field notes handed down by earlier geologists, he covered 10 or 15 miles a day, past countless sheep and the occasional farmer. “Their whole lives they’ve lived in these beautiful fjords,” he said. “They look up to these black, layered rocks, and I tell them that each one of those is a different volcanic eruption with a lava flow. It blows their minds!” He laughed. “It blows my mind even more that they never realized it!”

    The olivine erupted to Earth’s surface in those very lava flows between 10 and 17 million years ago. Jackson, like many geologists, believes that the source of the eruptions was the Iceland plume, a hypothetical upwelling of solid rock that may rise, like the globules in a lava lamp, from deep inside Earth. The plume, if it exists, would now underlie the active volcanoes of central Iceland. In the past, it would have surfaced here at the fjords, back in the days when here was there — before the puzzle-piece of Earth’s crust upon which Iceland lies scraped to the northwest.

    Other modern findings [Nature]about olivine from the region suggest that it might derive from an ancient reservoir of minerals at the base of the Iceland plume that, over billions of years, never mixed with the rest of Earth’s interior. Jackson hoped the samples he collected would carry a chemical message from the reservoir and prove that it formed during the planet’s infancy — a period that until recently was inaccessible to science.

    After returning to California, he sent his samples to Richard Walker to ferret out that message. Walker, a geochemist at the University of Maryland, is processing the olivine to determine the concentration of the chemical isotope tungsten-182 in the rock relative to the more common isotope, tungsten-184. If Jackson is right, his samples will join a growing collection of rocks from around the world whose abnormal tungsten isotope ratios have completely surprised scientists. These tungsten anomalies reflect processes that could only have occurred within the first 50 million years of the solar system’s history, a formative period long assumed to have been wiped from the geochemical record by cataclysmic collisions that melted Earth and blended its contents.

    The anomalies “are giving us information about some of the earliest Earth processes,” Walker said. “It’s an alternative universe from what geochemists have been working with for the past 50 years.”

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    Matt Jackson and his family with a local farmer in northwest Iceland. Courtesy of Matt Jackson.

    The discoveries are sending geologists like Jackson into the field in search of more clues to Earth’s formation — and how the planet works today. Modern Earth, like early Earth, remains poorly understood, with unanswered questions ranging from how volcanoes work and whether plumes really exist to where oceans and continents came from, and what the nature and origin might be of the enormous structures, colloquially known as “blobs,” that seismologists detect deep down near Earth’s core. All aspects of the planet’s form and function are interconnected. They’re also entangled with the rest of the solar system. Any attempt, for instance, to explain why tectonic plates cover Earth’s surface like a jigsaw puzzle must account for the fact that no other planet in the solar system has plates. To understand Earth, scientists must figure out how, in the context of the solar system, it became uniquely earthlike. And that means probing the mystery of the first tens of millions of years.

    “You can think about this as an initial-conditions problem,” said Michael Manga, a geophysicist at the University of California, Berkeley, who studies geysers and volcanoes. “The Earth we see today evolved from something. And there’s lots of uncertainty about what that initial something was.”

    Pieces of the Puzzle

    On one of an unbroken string of 75-degree days in Santa Barbara the week before Jackson left for Iceland, he led a group of earth scientists on a two-mile beach hike to see some tar dikes — places where the sticky black material has oozed out of the cliff face at the back of the beach, forming flabby, voluptuous folds of faux rock that you can dent with a finger. The scientists pressed on the tar’s wrinkles and slammed rocks against it, speculating about its subterranean origin and the ballpark range of its viscosity. When this reporter picked up a small tar boulder to feel how light it was, two or three people nodded approvingly.

    A mix of geophysicists, geologists, mineralogists, geochemists and seismologists, the group was in Santa Barbara for the annual Cooperative Institute for Dynamic Earth Research (CIDER) workshop at the Kavli Institute for Theoretical Physics. Each summer, a rotating cast of representatives from these fields meet for several weeks at CIDER to share their latest results and cross-pollinate ideas — a necessity when the goal is understanding a system as complex as Earth.

    Earth’s complexity, how special it is, and, above all, the black box of its initial conditions have meant that, even as cosmologists map the universe and astronomers scan the galaxy for Earth 2.0, progress in understanding our home planet has been surprisingly slow. As we trudged from one tar dike to another, Jackson pointed out the exposed sedimentary rock layers in the cliff face — some of them horizontal, others buckled and sloped. Amazingly, he said, it took until the 1960s for scientists to even agree that sloped sediment layers are buckled, rather than having piled up on an angle. Only then was consensus reached on a mechanism to explain the buckling and the ruggedness of Earth’s surface in general: the theory of plate tectonics.

    Projecting her voice over the wind and waves, Carolina Lithgow-Bertelloni, a geophysicist from University College London who studies tectonic plates, credited the German meteorologist Alfred Wegener for first floating the notion of continental drift in 1912 to explain why Earth’s landmasses resemble the dispersed pieces of a puzzle. “But he didn’t have a mechanism — well, he did, but it was crazy,” she said.

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    Earth scientists on a beach hike in Santa Barbara County, California. Natalie Wolchover/Quanta Magazine

    A few years later, she continued, the British geologist Sir Arthur Holmes convincingly argued that Earth’s solid-rock mantle flows fluidly on geological timescales, driven by heat radiating from Earth’s core; he speculated that this mantle flow in turn drives surface motion. More clues came during World War II. Seafloor magnetism, mapped for the purpose of hiding submarines, suggested that new crust forms at the mid-ocean ridge — the underwater mountain range that lines the world ocean like a seam — and spreads in both directions to the shores of the continents. There, at “subduction zones,” the oceanic plates slide stiffly beneath the continental plates, triggering earthquakes and carrying water downward, where it melts pockets of the mantle. This melting produces magma that rises to the surface in little-understood fits and starts, causing volcanic eruptions. (Volcanoes also exist far from any plate boundaries, such as in Hawaii and Iceland. Scientists currently explain this by invoking the existence of plumes, which researchers like Walker and Jackson are starting to verify and map using isotope studies.)

    The physical description of the plates finally came together in the late 1960s, Lithgow-Bertelloni said, when the British geophysicist Dan McKenzie and the American Jason Morgan separately proposed a quantitative framework for modeling plate tectonics on a sphere.

    The tectonic plates of the world were mapped in 1996, USGS.
    The tectonic plates of the world were mapped in 1996, USGS.

    Other than their existence, almost everything about the plates remains in contention. For instance, what drives their lateral motion? Where do subducted plates end up — perhaps these are the blobs? — and how do they affect Earth’s interior dynamics? Why did Earth’s crust shatter into plates in the first place when no other planetary surface in the solar system did? Also completely mysterious is the two-tier architecture of oceanic and continental plates, and how oceans and continents came to ride on them — all possible prerequisites for intelligent life. Knowing more about how Earth became earthlike could help us understand how common earthlike planets are in the universe and thus how likely life is to arise.

    The continents probably formed, Lithgow-Bertelloni said, as part of the early process by which gravity organized Earth’s contents into concentric layers: Iron and other metals sank to the center, forming the core, while rocky silicates stayed in the mantle. Meanwhile, low-density materials buoyed upward, forming a crust on the surface of the mantle like soup scum. Perhaps this scum accumulated in some places to form continents, while elsewhere oceans materialized.

    Figuring out precisely what happened and the sequence of all of these steps is “more difficult,” Lithgow-Bertelloni said, because they predate the rock record and are “part of the melting process that happens early on in Earth’s history — very early on.”

    Until recently, scientists knew of no geochemical traces from so long ago, and they thought they might never crack open the black box from which Earth’s most glorious features emerged. But the subtle anomalies in tungsten and other isotope concentrations are now providing the first glimpses of the planet’s formation and differentiation. These chemical tracers promise to yield a combination timeline-and-map of early Earth, revealing where its features came from, why, and when.

    A Sketchy Timeline

    Humankind’s understanding of early Earth took its first giant leap when Apollo astronauts brought back rocks from the moon: our tectonic-less companion whose origin was, at the time, a complete mystery.

    The rocks “looked gray, very much like terrestrial rocks,” said Fouad Tera, who analyzed lunar samples at the California Institute of Technology between 1969 and 1976. But because they were from the moon, he said, they created “a feeling of euphoria” in their handlers. Some interesting features did eventually show up: “We found glass spherules — colorful, beautiful — under the microscope, green and yellow and orange and everything,” recalled Tera, now 85. The spherules probably came from fountains that gushed from volcanic vents when the moon was young. But for the most part, he said, “the moon is not really made out of a pleasing thing — just regular things.”

    In hindsight, this is not surprising: Chemical analysis at Caltech and other labs indicated that the moon formed from Earth material, which appears to have gotten knocked into orbit when the 60 to 100 million-year-old proto-Earth collided with another protoplanet in the crowded inner solar system. This “giant impact” hypothesis of the moon’s formation [Science Direct], though still hotly debated [Nature]in its particulars, established a key step on the timeline of the Earth, moon and sun that has helped other steps fall into place.

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    A panorama of the Taurus-Littrow Valley created from photographs by Apollo 17 astronaut Eugene Cernan. Astronaut Harrison Schmitt is shown using a rake to collect samples. NASA

    Chemical analysis of meteorites is helping scientists outline even earlier stages of our solar system’s timeline, including the moment it all began.

    First, 4.57 billion years ago, a nearby star went supernova, spewing matter and a shock wave into space. The matter included radioactive elements that immediately began decaying, starting the clocks that isotope chemists now measure with great precision. As the shock wave swept through our cosmic neighborhood, it corralled the local cloud of gas and dust like a broom; the increase in density caused the cloud to gravitationally collapse, forming a brand-new star — our sun — surrounded by a placenta of hot debris.

    Over the next tens of millions of years, the rubble field surrounding the sun clumped into bigger and bigger space rocks, then accreted into planet parts called “planetesimals,” which merged into protoplanets, which became Mercury, Venus, Earth and Mars — the four rocky planets of the inner solar system today. Farther out, in colder climes, gas and ice accreted into the giant planets.

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    The planets of the solar system as depicted by a NASA computer illustration. Orbits and sizes are not shown to scale.
    Credit: NASA

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    Researchers use liquid chromatography to isolate elements for analysis. Rock samples dissolved in acid flow down ion-exchange columns, like the ones in Rick Carlson’s laboratory at the Carnegie Institution in Washington, to separate the elements. Mary Horan.

    The last of the Earth-melting “giant impacts” appears to have been the one that formed the moon; while subtracting the moon’s mass, the impactor was also the last major addition to Earth’s mass. Perhaps, then, this point on the timeline — at least 60 million years after the birth of the solar system and, counting backward from the present, at most 4.51 billion years ago — was when the geochemical record of the planet’s past was allowed to begin. “It’s at least a compelling idea to think that this giant impact that disrupted a lot of the Earth is the starting time for geochronology,” said Rick Carlson, a geochemist at the Carnegie Institution of Washington. In those first 60 million years, “the Earth may have been here, but we don’t have any record of it because it was just erased.”

    Another discovery from the moon rocks came in 1974. Tera, along with his colleague Dimitri Papanastassiou and their boss, Gerry Wasserburg, a towering figure in isotope cosmochemistry who died in June, combined many isotope analyses of rocks from different Apollo missions on a single plot, revealing a straight line called an “isochron” that corresponds to time. “When we plotted our data along with everybody else’s, there was a distinct trend that shows you that around 3.9 billion years ago, something massive imprinted on all the rocks on the moon,” Tera said.

    As the infant Earth navigated the crowded inner solar system, it would have experienced frequent, white-hot collisions, which were long assumed to have melted the entire planet into a global “magma ocean.” During these melts, gravity differentiated Earth’s liquefied contents into layers — core, mantle and crust. It’s thought that each of the global melts would have destroyed existing rocks, blending their contents and removing any signs of geochemical differences left over from Earth’s initial building blocks.

    The last of the Earth-melting “giant impacts” appears to have been the one that formed the moon; while subtracting the moon’s mass, the impactor was also the last major addition to Earth’s mass. Perhaps, then, this point on the timeline — at least 60 million years after the birth of the solar system and, counting backward from the present, at most 4.51 billion years ago — was when the geochemical record of the planet’s past was allowed to begin. “It’s at least a compelling idea to think that this giant impact that disrupted a lot of the Earth is the starting time for geochronology,” said Rick Carlson, a geochemist at the Carnegie Institution of Washington. In those first 60 million years, “the Earth may have been here, but we don’t have any record of it because it was just erased.”

    Another discovery from the moon rocks came in 1974. Tera, along with his colleague Dimitri Papanastassiou and their boss, Gerry Wasserburg, a towering figure in isotope cosmochemistry who died in June, combined many isotope analyses of rocks from different Apollo missions on a single plot, revealing a straight line called an “isochron” that corresponds to time. “When we plotted our data along with everybody else’s, there was a distinct trend that shows you that around 3.9 billion years ago, something massive imprinted on all the rocks on the moon,” Tera said.

    Wasserburg dubbed the event the “lunar cataclysm.” [Science Direct]. Now more often called the “late heavy bombardment,” it was a torrent of asteroids and comets that seems to have battered the moon 3.9 billion years ago, a full 600 million years after its formation, melting and chemically resetting the rocks on its surface. The late heavy bombardment surely would have rained down even more heavily on Earth, considering the planet’s greater size and gravitational pull. Having discovered such a momentous event in solar system history, Wasserburg left his younger, more reserved colleagues behind and “celebrated in Pasadena in some bar,” Tera said.

    As of 1974, no rocks had been found on Earth from the time of the late heavy bombardment. In fact, Earth’s oldest rocks appeared to top out at 3.8 billion years. “That number jumps out at you,” said Bill Bottke, a planetary scientist at the Southwest Research Institute in Boulder, Colorado. It suggests, Bottke said, that the late heavy bombardment might have melted whatever planetary crust existed 3.9 billion years ago, once again destroying the existing geologic record, after which the new crust took 100 million years to harden.

    In 2005, a group of researchers working in Nice, France, conceived of a mechanism to explain the late heavy bombardment — and several other mysteries about the solar system, including the curious configurations of Jupiter, Saturn, Uranus and Neptune, and the sparseness of the asteroid and Kuiper belts. Their “Nice model” [Nature] posits that the gas and ice giants suddenly destabilized in their orbits sometime after formation, causing them to migrate. Simulations by Bottke and others indicate that the planets’ migrations would have sent asteroids and comets scattering, initiating something very much like the late heavy bombardment. Comets that were slung inward from the Kuiper belt during this shake-up might even have delivered water to Earth’s surface, explaining the presence of its oceans.

    With this convergence of ideas, the late heavy bombardment became widely accepted as a major step on the timeline of the early solar system. But it was bad news for earth scientists, suggesting that Earth’s geochemical record began not at the beginning, 4.57 billion years ago, or even at the moon’s beginning, 4.51 billion years ago, but 3.8 billion years ago, and that most or all clues about earlier times were forever lost.

    Extending the Rock Record

    More recently, the late heavy bombardment theory and many other long-standing assumptions about the early history of Earth and the solar system have come into question, and Earth’s dark age has started to come into the light. According to Carlson, “the evidence for this 3.9 [billion-years-ago] event is getting less clear with time.” For instance, when meteorites are analyzed for signs of shock, “they show a lot of impact events at 4.2, 4.4 billion,” he said. “This 3.9 billion event doesn’t show up really strong in the meteorite record.” He and other skeptics of the late heavy bombardment argue that the Apollo samples might have been biased. All the missions landed on the near side of the moon, many in close proximity to the Imbrium basin (the moon’s biggest shadow, as seen from Earth), which formed from a collision 3.9 billion years ago. Perhaps all the Apollo rocks were affected by that one event, which might have dispersed the melt from the impact over a broad swath of the lunar surface. This would suggest a cataclysm that never occurred.

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    Lucy Reading-Ikkanda for Quanta Magazine

    Furthermore, the oldest known crust on Earth is no longer 3.8 billion years old. Rocks have been found in two parts of Canada dating to 4 billion and an alleged 4.28 billion years ago, refuting the idea that the late heavy bombardment fully melted Earth’s mantle and crust 3.9 billion years ago. At least some earlier crust survived.

    In 2008, Carlson and collaborators reported the evidence of 4.28 billion-year-old rocks in the Nuvvuagittuq greenstone belt in Canada. When Tim Elliott, a geochemist at the University of Bristol, read about the Nuvvuagittuq findings, he was intrigued to see that Carlson had used a dating method also used in earlier work by French researchers that relied on a short-lived radioactive isotope system called samarium-neodymium. Elliott decided to look for traces of an even shorter-lived system — hafnium-tungsten — in ancient rocks, which would point back to even earlier times in Earth’s history.

    The dating method works as follows: Hafnium-182, the “parent” isotope, has a 50 percent chance of decaying into tungsten-182, its “daughter,” every 9 million years (this is the parent’s “half-life”). The halving quickly reduces the parent to almost nothing; by 50 million years after the supernova that sparked the sun, virtually all the hafnium-182 would have become tungsten-182.

    That’s why the tungsten isotope ratio in rocks like Matt Jackson’s olivine samples can be so revealing: Any variation in the concentration of the daughter isotope, tungsten-182, measured relative to tungsten-184 must reflect processes that affected the parent, hafnium-182, when it was around — processes that occurred during the first 50 million years of solar system history. Elliott knew that this kind of geochemical information was previously believed to have been destroyed by early Earth melts and billions of years of subsequent mantle convection. But what if it wasn’t?

    Elliott contacted Stephen Moorbath, then an emeritus professor of geology at the University of Oxford and “one of the grandfather figures in finding the oldest rocks,” Elliott said. Moorbath “was keen, so I took the train up.” Moorbath led Elliott down to the basement of Oxford’s earth science building, where, as in many such buildings, a large collection of rocks shares the space with the boiler and stacks of chairs. Moorbath dug out specimens from the Isua complex in Greenland, an ancient bit of crust that he had pegged, in the 1970s, at 3.8 billion years old.

    Elliott and his student Matthias Willbold powdered and processed the Isua samples and used painstaking chemical methods to extract the tungsten. They then measured the tungsten isotope ratio using state-of-the-art mass spectrometers. In a 2011 Nature paper, Elliott, Willbold and Moorbath, who died in October, reported that the 3.8 billion-year-old Isua rocks contained 15 parts per million more tungsten-182 than the world average — the first ever detection of a “positive” tungsten anomaly on the face of the Earth.

    The paper scooped Richard Walker of Maryland and his colleagues, who months later reported [Science] a positive tungsten anomaly in 2.8 billion-year-old komatiites from Kostomuksha, Russia.

    Although the Isua and Kostomuksha rocks formed on Earth’s surface long after the extinction of hafnium-182, they apparently derive from materials with much older chemical signatures. Walker and colleagues argue that the Kostomuksha rocks must have drawn from hafnium-rich “primordial reservoirs” in the interior that failed to homogenize during Earth’s early mantle melts. The preservation of these reservoirs, which must trace to the first 50 million years and must somehow have survived even the moon-forming impact, “indicates that the mantle may have never been well mixed,” Walker and his co-authors wrote. That raises the possibility of finding many more remnants of Earth’s early history.

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    The 60 million-year-old flood basalts of Baffin Bay, Greenland, sampled by the geochemist Hanika Rizo (center) and colleagues, contain isotope traces that originated more than 4.5 billion years ago. Don Francis (left); courtesy of Hanika Rizo (center and right).

    The researchers say they will be able to use tungsten anomalies and other isotope signatures in surface material as tracers of the ancient interior, extrapolating downward and backward into the past to map proto-Earth and reveal how its features took shape. “You’ve got the precision to look and actually see the sequence of events occurring during planetary formation and differentiation,” Carlson said. “You’ve got the ability to interrogate the first tens of millions of years of Earth’s history, unambiguously.”

    Anomalies have continued to show up in rocks of various ages and provenances. In May, Hanika Rizo of the University of Quebec in Montreal, along with Walker, Jackson and collaborators, reported in Science the first positive tungsten anomaly in modern rocks — 62 million-year-old samples from Baffin Bay, Greenland. Rizo hypothesizes that these rocks were brought up by a plume that draws from one of the “blobs” deep down near Earth’s core. If the blobs are indeed rich in tungsten-182, then they are not tectonic-plate graveyards as many geophysicists suspect, but instead date to the planet’s infancy. Rizo speculates that they are chunks of the planetesimals that collided to form Earth, and that the chunks somehow stayed intact in the process. “If you have many collisions,” she said, “then you have the potential to create this patchy mantle.” Early Earth’s interior, in that case, looked nothing like the primordial magma ocean pictured in textbooks.

    More evidence for the patchiness of the interior has surfaced. At the American Geophysical Union meeting earlier this month, Walker’s group reported [2016 AGU Fall Meeting] a negative tungsten anomaly — that is, a deficit of tungsten-182 relative to tungsten-184 — in basalts from Hawaii and Samoa. This and other isotope concentrations in the rocks suggest the hypothetical plumes that produced them might draw from a primordial pocket of metals, including tungsten-184. Perhaps these metals failed to get sucked into the core during planet differentiation.

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    Tim Elliott collecting samples of ancient crust rock in Yilgarn Craton in Western Australia. Tony Kemp

    Meanwhile, Elliott explains the positive tungsten anomalies in ancient crust rocks like his 3.8 billion-year-old Isua samples by hypothesizing that these rocks might have hardened on the surface before the final half-percent of Earth’s mass — delivered to the planet in a long tail of minor impacts — mixed into them. These late impacts, known as the “late veneer,” would have added metals like gold, platinum and tungsten (mostly tungsten-184) to Earth’s mantle, reducing the relative concentration of tungsten-182. Rocks that got to the surface early might therefore have ended up with positive tungsten anomalies.

    Other evidence complicates this hypothesis, however — namely, the concentrations of gold and platinum in the Isua rocks match world averages, suggesting at least some late veneer material did mix into them. So far, there’s no coherent framework that accounts for all the data. But this is the “discovery phase,” Carlson said, rather than a time for grand conclusions. As geochemists gradually map the plumes and primordial reservoirs throughout Earth from core to crust, hypotheses will be tested and a narrative about Earth’s formation will gradually crystallize.

    Elliott is working to test his late-veneer hypothesis. Temporarily trading his mass spectrometer for a sledgehammer, he collected a series of crust rocks in Australia that range from 3 billion to 3.75 billion years old. By tracking the tungsten isotope ratio through the ages, he hopes to pinpoint the time when the mantle that produced the crust became fully mixed with late-veneer material.

    “These things never work out that simply,” Elliott said. “But you always start out with the simplest idea and see how it goes.”

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 6:04 am on December 6, 2016 Permalink | Reply
    Tags: Geology, Inorganic geochemistry, Molecular environmental science, , ,   

    From Stanford: “Eureka moment leads to new method of studying environmental toxins” 

    Stanford University Name
    Stanford University

    March 31, 2016 [Stanford just saw fit to put this in social media.]
    Ker Than

    1
    View of the TVA Kingston Fossil Plant fly ash spill. Work using X-ray beams is clarifying how pollutants bind or release from solid surfaces and move into groundwater. Photo: Brian Stansberry via Wikimedia Commons

    A technique for probing the surface of particles revealed how toxins move from the soil to groundwater.

    In 1986, Gordon Brown used SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) to visualize something no one had ever seen before: the exact way that atoms bond to a solid surface.

    SLAC/SSRL
    SLAC/SSRL

    The work stemmed from a eureka moment that Brown had during the doctoral defense of graduate student Kim Hayes but has since grown into one of the seminal works in inorganic geochemistry, and even spawned a new field of study — molecular environmental science.

    Knowing how charged ions interact with solid surfaces is crucial for understanding how toxic metal ions such as lead, arsenic and mercury or radioactive elements such as uranium may be released from particles in soils and sediments and into groundwater or vice versa. Using the techniques Brown’s team helped pioneer, scientists today can paint exquisitely detailed pictures of how metal ions bind to different solid surfaces, including those on nanoparticles.

    “You can determine what other atoms are around the pollutant ions of interest, the inter-atomic distances separating them and the number and types of chemical bonds that keep them bound to the surface,” says Brown, a professor of geological sciences and of photon science. “This is crucial for understanding how easily they move from one place to another.”


    Access mp4 video here .

    Synchrotron-generated X-rays like those produced at SSRL are ideal for this type of investigation for a number of reasons, says John Bargar, a senior scientist at SLAC and Brown’s former PhD student. For one thing, synchrotron X-rays are highly focused, much like laser beams. “All of the photons produced are condensed into either a pencil beam or a narrow fan,” Bargar says. “That means you can use nearly all of the photons that you’re making with very little waste.”

    Another advantage of synchrotron X-rays, Brown says, is that their extremely high intensity makes it possible to detect and study pollutant ions at the very low concentration levels typically found in many polluted environmental samples.

    Moreover, synchrotron X-rays are polarized, meaning their waves vibrate primarily in a single plane. By modifying the direction of polarization, scientists can create very powerful probes for studying chemical bonds in molecules.

    “A metal ion sitting inside a larger molecule is surrounded by many bonds. Oftentimes, we don’t want to interrogate all of those bonds at once,” Bargar says. “With polarized X-rays, we can selectively interrogate the bonds in a specific orientation.”

    Recently, Brown and Bargar have collaborated to study how organic matter and live microbial organisms affect the binding affinities of different environmental pollutants to solid surfaces. Bargar and Brown are also investigating ways to harness bacterial aggregations called biofilms to neutralize the effects of environmental pollutants. In addition, they are also using synchrotron X-rays at SSRL to look for more efficient ways of safely extracting oil and gas from tight shales via hydraulic fracturing, a process that is transforming the energy landscape of the United States.

    “The X-ray beams synchrotrons are able to generate today are about 15 orders of magnitude brighter than what was available when I was a graduate student. This has led to a revolution in all areas of science and engineering,” Brown says. “I could collect the data for my entire PhD thesis in one morning at SSRL now.”

    See the full article here .

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  • richardmitnick 8:55 am on November 30, 2016 Permalink | Reply
    Tags: , , Geology, Ring of Fire, Scientists have found the largest exposed fault on Earth   

    From Science Alert: “Scientists have found the largest exposed fault on Earth” 

    ScienceAlert

    Science Alert

    29 NOV 2016
    BEC CREW

    1
    Pulau Banta island in the Banta Sea. Credit: Jialiang Gao/Wikimedia

    For the first time, researchers have confirmed the existence of the largest exposed fault on Earth, and it could explain how a 7.2-km-deep (4.5-mile) abyss formed in the Pacific Ocean.

    Discovered beneath the Banda Sea in eastern Indonesia, the massive fault plane runs right through the notorious Ring of Fire – an explosive region where roughly 90 percent of the world’s earthquakes and 75 percent of all active volcanoes occur.

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    SVG version of File:Pacific_Ring_of_Fire.png, recreated using WDB vector data using code mentioned in File:Worldmap_wdb_combined.svg. 11 February 2009. Gringer

    For almost a century, scientists have known about the Weber Deep – a massive chasm lurking near the Maluku Islands of Indonesia that forms the deepest point of Earth’s oceans not within a trench.

    But until now, no one could figure out how it formed.

    To investigate, geologists from the Australian National University (ANU) in Canberra and Royal Holloway University of London analysed maps of the sea floor taken from the Banda Sea region in the Pacific Ocean.

    They discovered that rocks sitting the bottom of the sea were cut by hundreds of straight parallel scars.

    Simulations of the sea floor suggested that a massive piece of crust bigger than Belgium was at some point ripped apart by a massive crack – or fault – in the oceanic plates to form a deep depression in the ocean floor.

    The activity appeared to have left behind the biggest exposed fault plane ever detected on Earth, which the researchers have tentatively called the Banda Detachment.

    When a fault forms in Earth’s crust, it forms two main features: a fault plane, which is the flat surface of a fault; and the fault line, which is the intersection of a fault plane with the ground surface.

    The team’s simulations showed that the Banda Detachment fault plane was exposed over an area of 60,000 square kilometres (23,166 square miles) when the sea floor cracked.

    “We had made a good argument for the existence of this fault we named the Banda Detachment, based on the bathymetry [underwater topography] data and on knowledge of the regional geology,” said one of the researchers, Gordon Lister from ANU.

    3
    Diagram showing the Banda Detachment fault beneath the Weber Deep basin. Credit: ANU

    But as far as the researchers were concerned, this massive fault didn’t exist until they saw evidence of it with their own eyes.

    When they sailed out in the Pacific Ocean in eastern Indonesia, they identified prominent landforms in the water that were formed by the Banda Detachment fault plane.

    “I was stunned to see the hypothesised fault plane, this time not on a computer screen, but poking above the waves,” says one of the team, Jonathan Pownall from ANU. “The discovery will help explain how one of Earth’s deepest sea areas became so deep.”

    The team says the fact that the Weber Deep abyss formed right where the Banda Detachment was exposed could help researchers figure out how it formed.

    “Our research found that a 7 km-deep abyss beneath the Banda Sea off eastern Indonesia was formed by extension along what might be Earth’s largest-identified exposed fault plane,” says Pownall.

    The discovery could also help geologists predict the movements of one of the most tectonically active regions in the world – the Pacific Ring of Fire, a 40,000-km (25,000-mile) stretch of ocean dotted with no less than 452 volcanoes, which is around 75 percent of the world’s total.

    “In a region of extreme tsunami risk, knowledge of major faults such as the Banda Detachment, which could make big earthquakes when they slip, is fundamental to being able to properly assess tectonic hazards,” says Pownall.

    The research has been published in Geology.

    See the full article here .

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  • richardmitnick 5:59 am on November 23, 2016 Permalink | Reply
    Tags: , , , Curtin University, Geology, Meteorite recovered in WA with the help of stargazers and science app   

    From CSIRO via ABC: “Meteorite recovered in WA with the help of stargazers and science app” 

    CSIRO bloc

    Commonwealth Scientific and Industrial Research Organisation

    1
    ABC

    11.21.16
    Colin Cosier

    2
    The pristine meteorite sample recovered from Morawa, protected by a non-reactive Teflon bag. Supplied: Curtin University

    A meteorite estimated to be older than Earth has been recovered from a West Australian farm with the help of some enthusiastic stargazers and a phone app.

    The 1.15-kilogram meteor landed near Morawa on Halloween, discovered days later by members of Curtin University’s Desert Fireball Network (DFN).

    DFN founder Phil Bland said the fireball was located with the help of four skyward-pointing outback cameras and reports made to the Fireballs in the Sky citizen science app.

    He said retrieving the meteorite so quickly meant it is in good condition and scientifically valuable.

    “Our team was able to track the fall line and calculate its landing spot to within 200 metres of where it was subsequently found,” Professor Bland said.

    “It [the meteorite] is a type called a chondrite, which is a type of meteorite which has not been cooked up enough to melt.

    “So it can give us some information about that period of early solar system history.”

    “We’re hopeful, because we managed to get it in a very pristine way, that we can find some quite soluble elements or minerals in there, or volatile minerals that can tell us about water and organics in the solar system.

    “Meteorites tell us pretty much everything we want to know about the solar system … but unless we know where they came from, there’s a really big piece of that puzzle left.”

    3
    Curtin University’s Desert Fireball Network camera used a 30-second exposure to pick up the fireball. Supplied: Curtin University

    Prof Bland said of the 50,000 meteorites that have been discovered, the origins of only 20 to 30 are known.

    Meteorites decelerate to a free-fall velocity by the time they hit the earth, travelling at the same speed as a rock thrown from a tall building.

    Before falling through the atmosphere, the meteorite is predicted to have been 50-100 times bigger than its current size.

    Martin Towner from the Department of Applied Geology described the rock as a pristine, unweathered and a fresh sample.

    He said there was no visible impact on the ground where it was found, about 300 kilometres north-east of Perth.

    DFN’s Ben Hartig said they were at the correct field when they first looked, but called it a day before they found the meteor.

    The next morning they looked in another paddock, before it was finally discovered in the original field.

    “It was right at the end of the field, so we pretty much all thought we’d finished off that field and we then we see this black rock,” Mr Hartig said.

    Founder of WA’s Stargazers Club, Carol Redford, was one of those who uploaded her location to the app when she saw the meteorite streak through the sky.

    “I immediately grabbed my smart phone and headed outside,” said Ms Redford, who is also known as Galaxy Girl.

    4
    Desert Fireball Network search team with recovered meteorite. Supplied: Curtin University

    See the full article here .

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    CSIRO, the Commonwealth Scientific and Industrial Research Organisation, is Australia’s national science agency and one of the largest and most diverse research agencies in the world.

     
  • richardmitnick 8:41 am on October 14, 2016 Permalink | Reply
    Tags: , , , Geology, Microtektites, Signs of comet collision found in 5.5-million-year-old rocks, Spherules   

    From COSMOS: “Signs of comet collision found in 5.5-million-year-old rocks” 

    Cosmos Magazine bloc

    COSMOS

    14 October 2016
    Amy Middleton

    1
    Glass blobs in rocks found along the US east coast point to a comet collision a few million years ago. Marc Ward / Stocktrek Images / Getty Images

    Glassy spheres discovered in sedimentary rock have tipped off geologists about a previously unknown prehistoric comet crash – one that may have triggered a period of intense global warming.

    Morgan Schaller at the Rensselaer Polytechnic Institute in New York and colleagues found marble-like glassy spherules, known as microtektites, which they believe to be fragments of debris scattered into the air after an object collided with the Earth some 5.5 million years ago.

    They published their work in Science.

    2
    Examples of a few of the spherules examined in the study. M F Schaller et al, Science 2016

    The distinct structures and unique appearances of spherules, as well as the way they’re positioned in sediment, can offer clues about historic impact events.

    Schaller’s spherules were found in marine shelf sites on the Atlantic Coastal Plain, along the east coast of the US, dating back to the boundary between the Paleocene and Eocene epochs.

    This is known as the Paleocene-Eocene Thermal Maximum (PETM), one of the most dramatic climate events known to science.

    During this period, the global average temperature was 8 °C higher than it is today and the world largely devoid of ice. Massive amounts of carbon were injected into the atmosphere and oceans and many of the world’s organisms experienced drastic shifts in their evolution.

    This intense warming is particularly relevant to us, because it marks the closest comparative event to the global warming evident today.

    What may have kick-started the PETM is hotly debated, and theories stretch from volcanic degassing to the cycle of Earth’s orbit. Now, the possibility of a meteorite impact may be thrown into the mix.

    To draw clues from the spherules, the researchers analysed the size, structure, layout and abundance of the particles they had uncovered, and compared the data to evidence of other impact sites.

    Shape and colour of the fragments also offered clues about their origins.

    “The spherules often have surface pits and in some cases microcraters,” the researchers write, “indicating relative velocities high enough to fracture the spherules on impact with one another, or other objects, after solidification.”

    Not everyone’s convinced, though.

    Christian Koeberl, an impact specialist at the University of Vienna in Austria, said the spherules could have come from another time and been reworked into the PETM sediments.

    The researchers did not directly use radiometric dating on the spherules themselves – just the surrounding sediment.

    But the next step, according to the research team, is to uncover spherules in more locations and start to figure out how far the debris spread. This will help them eventually narrow down a potential crater location to mark the comet’s impact.

    See the full article here .

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  • richardmitnick 8:09 am on October 12, 2016 Permalink | Reply
    Tags: , , Geology, , , , ,   

    From Symmetry: “Recruiting team geoneutrino” 

    Symmetry Mag
    Symmetry

    10/11/16
    Leah Crane

    1
    Illustration by Sandbox Studio, Chicago with Corinne Mucha

    Physicists and geologists are forming a new partnership to study particles from inside the planet.

    The Earth is like a hybrid car.

    Deep under its surface, it has two major fuel tanks. One is powered by dissipating primordial energy left over from the planet’s formation. The other is powered by the heat that comes from radioactive decay.

    We have only a shaky understanding of these heat sources, says William McDonough, a geologist at the University of Maryland. “We don’t have a fuel gauge on either one of them. So we’re trying to unravel that.”

    One way to do it is to study geoneutrinos, a byproduct of the process that burns Earth’s fuel. Neutrinos rarely interact with other matter, so these particles can travel straight from within the Earth to its surface and beyond.

    Geoneutrinos hold clues as to how much radioactive material the Earth contains. Knowing that could lead to insights about how our planet formed and its modern-day dynamics. In addition, the heat from radioactive decay plays a key role in driving plate tectonics.

    The tectonic plates of the world were mapped in 1996, USGS.
    The tectonic plates of the world were mapped in 1996, USGS

    Understanding the composition of the planet and the motion of the plates could help geologists model seismic activity.

    To effectively study geoneutrinos, scientists need knowledge both of elementary particles and of the Earth itself. The problem, McDonough says, is that very few geologists understand particle physics, and very few particle physicists understand geology. That’s why physicists and geologists have begun coming together to build an interdisciplinary community.

    “There’s really a need for a beyond-superficial understanding of the physics for the geologists and likewise a nonsuperficial understanding of the Earth by the physicists,” McDonough says, “and the more that we talk to each other, the better off we are.”

    There are hurdles to overcome in order to get to that conversation, says Livia Ludhova, a neutrino physicist and geologist affiliated with Forschungzentrum Jülich and RWTH Aachen University in Germany. “I think the biggest challenge is to make a common dictionary and common understanding—to get a common language. At the basic level, there are questions on each side which can appear very naïve.”

    In July, McDonough and Gianpaolo Bellini, emeritus scientist of the Italian National Institute of Nuclear Physics and retired physics professor at the University of Milan, led a summer institute for geology and physics graduate students to bridge the divide.

    “In general, geology is more descriptive,” Bellini says. “Physics is more structured.”

    This can be especially troublesome when it comes to numerical results, since most geologists are not used to working with the defined errors that are so important in particle physics.

    At the summer institute, students began with a sort of remedial “preschool,” in which geologists were taught how to interpret physical uncertainty and the basics of elementary particles and physicists were taught about Earth’s interior. Once they gained basic knowledge of one another’s fields, the scientists could begin to work together.

    This is far from the first interdisciplinary community within science or even particle physics. Ludhova likens it to the field of radiology: There is one expert to take an X-ray and another to determine a plan of action once all the information is clear. Similarly, particle physicists know how to take the necessary measurements, and geologists know what kinds of questions they could answer about our planet.

    Right now, only two major experiments are looking for geoneutrinos: KamLAND at the Kamioka Observatory in Japan and Borexino at the Gran Sasso National Laboratory in Italy. Between the two of them, these observatories detect fewer than 20 geoneutrinos a year.

    KamLAND
    KamLAND at the Kamioka Observatory in Japan

    INFN/Borexino Solar Neutrino detector, Gran Sasso, Italy
    INFN/Borexino Solar Neutrino detector, Gran Sasso, Italy

    Between the two of them, these observatories detect fewer than 20 geoneutrinos a year.

    Because of the limited results, geoneutrino physics is by necessity a small discipline: According to McDonough, there are only about 25 active neutrino researchers with a deep knowledge of both geology and physics.

    Over the next decade, though, several more neutrino detectors are anticipated, some of which will be much larger than KamLAND or Borexino. The Jiangmen Underground Neutrino Observatory (JUNO) in China, for example, should be ready in 2020.

    JUNO Neutrino detector China
    JUNO Neutrino detector China

    Whereas Borexino’s detector is made up of 300 tons of active material, and KamLAND’s contains 1000, JUNO’s will have 20,000 tons.

    The influx of data over the next decade will allow the community to emerge into the larger scientific scene, Bellini says. “There are some people who say ‘now this is a new era of science’—I think that is exaggerated. But I do think that we have opened a new chapter of science in which we use the methods of particle physics to study the Earth.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:15 pm on October 10, 2016 Permalink | Reply
    Tags: , , Geology, Intertropical Convergence Zone, Paleoceanography, Paleography   

    From Eos: “Simulating the Climate 145 Million Years Ago” 

    Eos news bloc

    Eos

    10.10.16
    Shannon Hall

    A new model shows that the Intertropical Convergence Zone wasn’t always a single band around the equator, which had drastic effects on climate.

    1
    Upper Jurassic (145- to 160-million-year-old) finely laminated organic carbon-rich shale interspersed with homogeneous, low-carbon mudrock of the Kimmeridge Clay Formation in Kimmeridge Bay, England. Variation in rock type reflects the ocean response to a monsoon-like climate 30°N during the Late Jurassic. Credit: Howard Armstrong

    The United Kingdom was once a lush oasis. That can be read from sediments within the Kimmeridge Clay Formation, which were deposited around 160 to 145 million years ago on Dorset’s “Jurassic Coast.” A favorite stomping ground for fossil hunters and the source rock for North Sea oil, the formation is rich in organic matter, which suggests that it likely formed when global greenhouse conditions were at least 4 times higher than present levels.

    Normally, organic matter disappears rapidly after an organism dies, as the nutrients are consumed by other life forms and the carbon decays. However, when the seas are starved of oxygen, which occurs when plankton numbers swell owing to increasing levels of carbon dioxide, then organic matter is preserved. An abundance of so-called black shales, or organic-rich muds, within the Kimmeridge Clay Formation points to this past.

    Here Armstrong et al. used those black shales to build new climate simulations that better approximate the climate toward the end of the Jurassic period. The model simulated 1422 years of time that suggested a radically different Intertropical Convergence Zone—the region where the Northern and Southern Hemisphere trade winds meet—than the one today. The convergence of these trade winds produces a global belt of clouds near the equator and is responsible for most of the precipitation on Earth.

    2
    This figure shows the path (in red) of the Intertropical Convergence Zone as it forks, where the Pacific Ocean met the western coast of the American continents. Credit: Armstrong et al. [2016]

    Today the Intertropical Convergence Zone in the Atlantic strays, at most, 12° away from the equator. However, 145 million years ago, when the continents were still much closer together, the model showed that the zone split, like a fork in the road, where the Pacific Ocean met the western coast of the American continents. The zone was driven apart by the proto-Appalachian mountain range to the north and the North African mountains to the south. The northern fork, which was much stronger than the southern one, extended as far as about 30° north, passing over the United Kingdom and the location of the Kimmeridge Clay Formation.

    Not only were the researchers able to verify that the United Kingdom was once a tropical oasis, but they were also able to simulate and map the climate 145 million years ago—research that will help scientists better understand how Earth will react to anthropogenic warming today and in the future. (Paleoceanography, doi:10.1002/2015PA002911, 2016)

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 5:26 pm on October 7, 2016 Permalink | Reply
    Tags: , , Geology, New insights into early terrestrial planet formation,   

    From Tokyo Tech: “New insights into early terrestrial planet formation” 

    tokyo-tech-bloc

    Tokyo Institute of Technology

    October 7, 2016
    No writer credit

    Scientists at Tokyo Tech have demonstrated that the relatively high levels of precious metals (gold, platinum, etc.) in the Earth’s mantle likely originated from one large-scale planetary impact prior to the formation of the Earth’s crust. This implies that the early Earth was a more benign place than previously thought, with fewer impacts from space.

    The debate surrounding the formation of the planets in our solar system, particularly the terrestrial (‘rocky’) planets, has been ongoing for many years. Scientists have long used computer models coupled with analysis of ancient meteorites to piece together the most likely scenarios that led to the planets forming as we know them today. A few puzzles still remain, including why Mars is much smaller than most models predict, and why the Earth in particular has a large amount of iron-loving, or ‘siderophile’, material in its mantle. Metals like gold, platinum and palladium would ordinarily be sequestered in the metallic core. The existing explanation for the latter is that the Earth was pummelled by meteors in its early life, leaving the highly siderophile elements (HSE) beneath the crust.

    Now, Ramon Brasser and Shigeru Ida at the Earth-Life Science Institute at Tokyo Institute of Technology, Japan, together with an international team of researchers from the University of Colorado (USA), the University of Dundee (UK) and the University of Oslo (Norway), have shown that the Earth’s HSE budget was most likely the result of a single, large-scale impact from space rather than the slow accumulation of material from many smaller meteors. This single impact may or may not have been the same one that created the Moon.

    Brasser’s team simulated the evolution of the terrestrial planets up to 300 million years after their first formation, a much longer time-scale than in previous studies. They collated information regarding the precious metal budget of Earth, Moon and Mars, and data on lunar cratering, and ran simulations to determine the circumstances that would fit the observations.

    Their results show that the total mass of planetesimals – accumulations of planet-forming material floating in space – at the time of the event that formed the Moon was less than previously thought. Mars accumulated 0.06% of its total mass in meteors during the period of the late veneer on Earth. The single, large-scale impact that created Earth’s HSE complement was unique to Earth, and must have occurred before the crust had begun to form around 4.45 billion years ago. Brasser and his team have shown that the early Earth at the time of life’s emergence was not under a constant, intense bombardment from meteors as previously thought.

    Background
    The early solar system

    There is still much debate around the early formation and behaviour of the planets that orbit our Sun. While the initial formation processes for the terrestrial planets — accumulation of material into ‘planetesimals’ followed by the gradual growth into full-size planets — is well-researched, it has proven difficult to solve some of the more complex enigmas about the inner solar system.

    Recently, the ‘Grand Tack’ theory was proposed in which Jupiter shifted its path inwards towards the sun before tracking back to its current position. This movement, together with the formation of Saturn and its associated resonance with Jupiter, meant that the two gas planets pulled an immense amount of debris and material away from the inner solar system when they shifted back outwards. This accounts for the smaller size of Mars and for the current composition of the asteroid belt.

    Questions regarding the unexplained high levels of iron-loving material (highly siderophile element, or HSE) in the Earth’s mantle, and indeed beneath the crust of Mars, still remain.

    Implications of the current study

    By combining data from various sources and simulating the early evolution of the terrestrial planets using computer models incorporating the Grand Tack theory, Brasser and his team have provided new insights into the HSE conundrum. Their simulations suggest that the Earth’s mantle composition was altered primarily by one large-scale impact — possibly the same impact that created the Moon — rather than by a multitude of small meteor impacts. Their results also show that there was far less debris and material floating in the inner solar system by the time the Moon-forming event occurred than scientists had anticipated. This implies that the early Earth may have been a more benign place than previously thought, and the team suggest that their findings should be incorporated into future simulations of the early solar system.

    1
    The crescent Earth rises above the lunar horizon in this spectacular photograph taken from the Apollo 17 spacecraft in lunar orbit during final lunar landing mission in the Apollo program. Image Credit: NASA

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    Tokyo Tech is the top national university for science and technology in Japan with a history spanning more than 130 years. Of the approximately 10,000 students at the Ookayama, Suzukakedai, and Tamachi Campuses, half are in their bachelor’s degree program while the other half are in master’s and doctoral degree programs. International students number 1,200. There are 1,200 faculty and 600 administrative and technical staff members.

    In the 21st century, the role of science and technology universities has become increasingly important. Tokyo Tech continues to develop global leaders in the fields of science and technology, and contributes to the betterment of society through its research, focusing on solutions to global issues. The Institute’s long-term goal is to become the world’s leading science and technology university.

     
  • richardmitnick 7:23 am on October 7, 2016 Permalink | Reply
    Tags: , Case of Earth’s missing continental crust solved: It sank, Geology, ,   

    From U Chicago: “Case of Earth’s missing continental crust solved: It sank” 

    U Chicago bloc

    University of Chicago

    October 4, 2016
    Carla Reiter

    Mantle swallowed massive chunk of Eurasia and India, study finds

    1
    UChicago scientists have concluded that half the original mass of Eurasia and India disappeared into the Earth’s interior before the two continents began their slow-motion collision approximately 60 million years ago. The participating UChicago scientists are (from left) Miquela Ingalls, doctoral student in geophysical sciences; David Rowley, professor in geophysical sciences; and Albert Colman, assistant professor in geophysical sciences. Rowley holds a rock of the type they believe sank into the interior. Photo by Jean Lachat

    How do you make half the mass of two continents disappear? To answer that question, you first need to discover that it’s missing.

    That’s what a trio of University of Chicago geoscientists and their collaborator did, and their explanation for where the mass went significantly changes prevailing ideas about what can happen when continents collide. It also has important implications for our understanding of when the continents grew to their present size and how the chemistry of the Earth’s interior has evolved.

    The study, published online Sept. 19 in Nature Geoscience, examines the collision of Eurasia and India, which began about 60 million years ago, created the Himalayas and is still in (slow) progress. The scientists computed with unprecedented precision the amount of landmass, or “continental crust,” before and after the collision.

    “What we found is that half of the mass that was there 60 million years ago is missing from the earth’s surface today,“ said Miquela Ingalls, a graduate student in geophysical sciences who led the project as part of her doctoral work.

    The result was unexpectedly large. After considering all other ways the mass might be accounted for, the researchers concluded that so huge a mass discrepancy could only be explained if the missing chunk had gone back down into the Earth’s mantle—something geoscientists had considered more or less impossible on such a scale.

    When tectonic plates come together, something has to give.

    The tectonic plates of the world were mapped in 1996, USGS.
    The tectonic plates of the world were mapped in 1996, USGS

    According to plate tectonic theory, the surface of the Earth comprises a mosaic of about a dozen rigid plates in relative motion. These plates move atop the upper mantle, and plates topped with thicker, more buoyant continental crust ride higher than those topped with thinner oceanic crust. Oceanic crust can dip and slide into the mantle, where it eventually mixes together with the mantle material. But continental crust like that involved in the Eurasia-India collision is less dense, and geologists have long believed that when it meets the mantle, it is pushed back up like a beach ball in water, never mixing back in.

    Geology 101 miscreant

    “We’re taught in Geology 101 that continental crust is buoyant and can’t descend into the mantle,” Ingalls said. The new results throw that idea out the window.

    “We really have significant amounts of crust that have disappeared from the crustal reservoir, and the only place that it can go is into the mantle,” said David Rowley, a professor in geophysical sciences who is one of Ingalls’ advisors and a collaborator on the project. “It used to be thought that the mantle and the crust interacted only in a relatively minor way. This work suggests that, at least in certain circumstances, that’s not true.”

    The scientists’ conclusion arose out of meticulous calculations of the amount of mass there before and after the collision, and a careful accounting of all possible ways it could have been distributed. Computing the amount of crust “before” is a contentious problem involving careful dating of the ages of strata and reconstructions of past plate positions, Ingalls said. Previous workers have done similar calculations but have often tried to force the “before” and “after” numbers to balance, “trying to make the system match up with what we think we already know about how tectonics works.”

    Ingalls and collaborators made no such assumptions. They used recently revised estimates about plate movements to figure out how large the two plates were at the onset of collision, and synthesized more than 20 years’ worth of data on the geology of various regions of the Earth to calculate how thick the crust would have been.

    “By looking at all of the relevant data sets, we’ve been able to say what the mass of the crust was at the beginning of collision,” Rowley said.

    Limited options

    There were only a few places for the displaced crust to go after the collision: Some was thrust upward, forming the Himalayas, some was eroded and deposited as enormous sedimentary deposits in the oceans, and some was squeezed out the sides of the colliding plates, forming Southeast Asia.

    “But accounting for all of these different types of mass loss, we still find that half of the continental crust involved in this collision is missing today,” Ingalls said. “If we’ve accounted for all possible solutions at the surface, it means the remaining mass must have been recycled wholesale into the mantle.”

    If large areas of continental crust are recycled back into the mantle, scientists can at last explain some previously puzzling geochemistry. Elements including lead and uranium are periodically erupted from the mantle through volcanic activity. Such elements are relatively abundant in continental crust, but scarce in the mantle. Yet the composition of some mantle-derived rocks indicates that they have been contaminated by continental crust. So how did continental material mix back into the mantle?

    “The implication of our work is that, if we’re seeing the India-Asia collision system as an ongoing process over Earth’s history, there has been a continuous mixing of the continental crustal elements back into the mantle,” said Rowley. “And they can then be re-extracted and seen in some of those volcanic materials that come out of the mantle today.”

    Funding: National Science Foundation

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    An intellectual destination

    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.

     
  • richardmitnick 9:55 am on September 4, 2016 Permalink | Reply
    Tags: Anthropocene – the Age of Humans, , Geology   

    From EarthSky: “Experts declare Anthropocene has begun” 

    1

    EarthSky

    August 31, 2016
    Deborah Byrd

    1
    Nuclear test at Bikini Atoll, 1946. Image via U.S. Dept. of Energy.

    Has humanity become so prevalent and powerful on Earth that we’re now globally affecting the geologic record, the actual rock record used by geologists to divide the past into named blocks? If the answer is yes, should scientists declare we’ve entered a new geologic epoch? This week, a group of 35 scientists said, yes, we are globally affecting the rock record and, yes, we should officially consider a new epoch. They would name it the Anthropocene, meaning Age of Humans, a word first introduced by two scientists in the year 2000 that’s now gaining wider scientific acceptance. The Anthropocene Work Group reported this conclusion on Monday (August 29, 2016) to the 35th International Geological Congress going on this week in Cape Town, South Africa.

    If scientists decide to accept the Anthropocene into the Geologic Time Scale, they’ll have to decide when it began. Scientists speak of golden spikes in Earth’s sediment layers, events laid down in the rocks that clearly demarcate one geologic epoch from another.

    A widely known example of a golden spike occurred with the demise of the dinosaurs, 65 million years ago. Most scientists believe an asteroid strike ended their dominance, due to the discovery in the late 1970s of iridium in the rock record on all parts of Earth. Iridium is rare on Earth (found mostly in Earth’s core), but common in the rest of the solar system. This layer of iridium in the rock record is said to mark the time of the asteroid impact; it’s the golden spike that marks the end of the Cretaceous epoch.

    What would be the golden spike separating the Anthropocene – the Age of Humans – from the rest of history? The answer is arbitrary, and members of the Anthropocene Work Group do not entirely agree.

    But 28 of the 35 scientists do agree that the golden spike for the Anthropocene comes around the 1950s. That’s when the great acceleration began on Earth, when our human impacts intensified and began to happen globally, not just locally, scientists say.

    About 10 members of the Anthropocene Work Group said they felt the start of the Anthropocene would coincide with the beginning of nuclear bomb testing. It started in the late 1940s and caused radioactive elements to be dispersed across Earth and thus laid down in the rock record.

    Other group members pointed to other ongoing signs of the Age of Humans, however, which will ultimately find their way into the rock record, including plastic pollution, soot from power stations, aluminium and concrete particles and high levels of nitrogen and phosphate in soils, derived from artificial fertilizers.

    And so defining when and how the Anthropocene began – assuming scientists do accept it and include it in the Geologic Time Scale – is a task that lies ahead.

    2
    Plastics aren’t permanent. They’ll eventually break down into fragments that’ll become buried in Earth’s sediments. When future geologists uncover these fragments, they might point to the start of the Anthropocene. Image via Plastic Ocean Gyre blog.

    Colin Waters from the British Geological Survey is secretary to the Anthropocene Work Group. He told the BBC:

    “This is an update on where we are in our discussions.

    We’ve got to a point where we’ve listed what we think the Anthropocene means to us as a working group.

    The majority of us think it is real; that there is clearly something happening; that there are clearly signals in the environment that are recognizable and make the Anthropocene a distinct unit; and the majority of us think it would be justified to formally recognise it.

    That doesn’t mean it will be formalized, but we’re going to go through the procedure of putting in a submission.”

    3
    If the Anthropocene were formally defined as a geological epoch beginning in 1945, then newer structures – such as the Grant Marsh Interstate 94 bridge over the Missouri River in Bismarck, N.D. (foreground) – would be classified as Anthropocene. Older structures with or without recent updates, such as the Bismarck railroad bridge (center) would be classified as Holocene and Anthropocene. Photo via Joel M. Galloway, USGS.

    So the word Anthropocene, though not a part of the official scientific lexicon yet, is gaining acceptance among scientists. You can read more about the history of the word, which was coined in the year 2000 by atmospheric chemist Paul Crutzen and ecologist Eugene Stoermer in this article: What is the Anthropocene?

    By the way, scientists now speak of our geologic age – basically everything since the end of the last major Ice Age, corresponding to the rise of complex human civilizations – as the Holocene. Holo is from a Greek root meaning whole or entire. You sometimes hear the Holocene called the Recent age.

    Some have argued that the word Holocene is good enough to describe our human impact and that we don’t need the new term Anthropocene. There are arguments for and against including the Anthropocene in the Geologic Time Scale under the subheads multiple meanings and contrasting philosophies – and also hierarchy – in this article.

    In the meantime, just remember the word Anthropocene.

    You’ll be hearing more about it in the years ahead.

    4
    The Geologic Time Spiral from the U.S. Geologic Survey.

    Bottom line: The Anthropocene Work Group reported their conclusions on August 29, 2016 to the 35th International Geological Congress in Cape Town, South Africa. The group said that the new epoch Anthropocene should be considered for official inclusion in the Geological Time Scale.

    See the full article here .

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