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  • richardmitnick 5:10 pm on November 20, 2014 Permalink | Reply
    Tags: , , Geology   

    From Caltech: “Caltech Geologists Discover Ancient Buried Canyon in South Tibet” 

    Caltech Logo
    Caltech

    11/20/2014
    Kimm Fesenmaier

    A team of researchers from Caltech and the China Earthquake Administration has discovered an ancient, deep canyon buried along the Yarlung Tsangpo River in south Tibet, north of the eastern end of the Himalayas. The geologists say that the ancient canyon—thousands of feet deep in places—effectively rules out a popular model used to explain how the massive and picturesque gorges of the Himalayas became so steep, so fast.

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    The general location of the Himalayan range

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    This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge—the new discoveries falsify this hypothesis. Credit: Ping Wang

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    The wide valley floor of the Nyang River, a tributary of the Yarlung Tsangpo. Here, the valley floor of the paleocanyon lies at a depth of about 800 meters below the present-day river.
    Credit: Ping Wang

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    This Google Earth image looks down the Yarlung Tsangpo Valley towards the Namche Barwa (right) and Gyala Peri massifs (left). The confluence with the Nyang River (joining from the right) is shown in the foreground. Here, the valley floor is about 4 kilometers wide and the paleocanyon lies about 800-900 meters below the present-day river.
    Credit: Map data: Google, Mapabc.com, DigitalGlobe, and Cnes/Spot Image

    “I was extremely surprised when my colleagues, Jing Liu-Zeng and Dirk Scherler, showed me the evidence for this canyon in southern Tibet,” says Jean-Philippe Avouac, the Earle C. Anthony Professor of Geology at Caltech. “When I first saw the data, I said, ‘Wow!’ It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today. That was a big discovery, in my opinion.”

    Geologists like Avouac and his colleagues, who are interested in tectonics—the study of the earth’s surface and the way it changes—can use tools such as GPS and seismology to study crustal deformation that is taking place today. But if they are interested in studying changes that occurred millions of years ago, such tools are not useful because the activity has already happened. In those cases, rivers become a main source of information because they leave behind geomorphic signatures that geologists can interrogate to learn about the way those rivers once interacted with the land—helping them to pin down when the land changed and by how much, for example.

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    World plate tectonics

    “In tectonics, we are always trying to use rivers to say something about uplift,” Avouac says. “In this case, we used a paleocanyon that was carved by a river. It’s a nice example where by recovering the geometry of the bottom of the canyon, we were able to say how much the range has moved up and when it started moving.”

    The team reports its findings in the current issue of Science.

    Last year, civil engineers from the China Earthquake Administration collected cores by drilling into the valley floor at five locations along the Yarlung Tsangpo River. Shortly after, former Caltech graduate student Jing Liu-Zeng, who now works for that administration, returned to Caltech as a visiting associate and shared the core data with Avouac and Dirk Scherler, then a postdoc in Avouac’s group. Scherler had previously worked in the far western Himalayas, where the Indus River has cut deeply into the Tibetan Plateau, and immediately recognized that the new data suggested the presence of a paleocanyon.

    Liu-Zeng and Scherler analyzed the core data and found that at several locations there were sedimentary conglomerates, rounded gravel and larger rocks cemented together, that are associated with flowing rivers, until a depth of 800 meters or so, at which point the record clearly indicated bedrock. This suggested that the river once carved deeply into the plateau.

    To establish when the river switched from incising bedrock to depositing sediments, they measured two isotopes, beryllium-10 and aluminum-26, in the lowest sediment layer. The isotopes are produced when rocks and sediment are exposed to cosmic rays at the surface and decay at different rates once buried, and so allowed the geologists to determine that the paleocanyon started to fill with sediment about 2.5 million years ago.

    The researchers’ reconstruction of the former valley floor showed that the slope of the river once increased gradually from the Gangetic Plain to the Tibetan Plateau, with no sudden changes, or knickpoints. Today, the river, like most others in the area, has a steep knickpoint where it meets the Himalayas, at a place known as the Namche Barwa massif. There, the uplift of the mountains is extremely rapid (on the order of 1 centimeter per year, whereas in other areas 5 millimeters per year is more typical) and the river drops by 2 kilometers in elevation as it flows through the famous Tsangpo Gorge, known by some as the Yarlung Tsangpo Grand Canyon because it is so deep and long.

    Combining the depth and age of the paleocanyon with the geometry of the valley, the geologists surmised that the river existed in this location prior to about 3 million years ago, but at that time, it was not affected by the Himalayas. However, as the Indian and Eurasian plates continued to collide and the mountain range pushed northward, it began impinging on the river. Suddenly, about 2.5 million years ago, a rapidly uplifting section of the mountain range got in the river’s way, damming it, and the canyon subsequently filled with sediment.

    “This is the time when the Namche Barwa massif started to rise, and the gorge developed,” says Scherler, one of two lead authors on the paper and now at the GFZ German Research Center for Geosciences in Potsdam, Germany.

    That picture of the river and the Tibetan Plateau, which involves the river incising deeply into the plateau millions of years ago, differs quite a bit from the typically accepted geologic vision. Typically, geologists believe that when rivers start to incise into a plateau, they eat at the edges, slowly making their way into the plateau over time. However, the rivers flowing across the Himalayas all have strong knickpoints and have not incised much at all into the Tibetan Plateau. Therefore, the thought has been that the rapid uplift of the Himalayas has pushed the rivers back, effectively pinning them, so that they have not been able to make their way into the plateau. But that explanation does not work with the newly discovered paleocanyon.

    The team’s new hypothesis also rules out a model that has been around for about 15 years, called tectonic aneurysm, which suggests that the rapid uplift seen at the Namche Barwa massif was triggered by intense river incision. In tectonic aneurysm, a river cuts down through the earth’s crust so fast that it causes the crust to heat up, making a nearby mountain range weaker and facilitating uplift.

    The model is popular among geologists, and indeed Avouac himself published a modeling paper in 1996 that showed the viability of the mechanism. “But now we have discovered that the river was able to cut into the plateau way before the uplift happened,” Avouac says, “and this shows that the tectonic aneurysm model was actually not at work here. The rapid uplift is not a response to river incision.”

    The other lead author on the paper, Tectonic control of Yarlung Tsangpo Gorge revealed by a buried canyon in Southern Tibet, is Ping Wang of the State Key Laboratory of Earthquake Dynamics, in Beijing, China. Additional authors include Jürgen Mey, of the University of Potsdam, in Germany; and Yunda Zhang and Dingguo Shi of the Chengdu Engineering Corporation, in China. The work was supported by the National Natural Science Foundation of China, the State Key Laboratory for Earthquake Dynamics, and the Alexander von Humboldt Foundation.

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 9:06 am on November 14, 2014 Permalink | Reply
    Tags: , Geology,   

    From Huff Post: “Scientists Venture Deep Inside Mysterious Siberian Crater And Come Back With Incredible Photos” 

    Huffington Post
    The Huffington Post

    11/13/2014
    Macrina Cooper-White

    Scientists are closing in on what caused three massive holes to open up mysteriously in northern Siberia last July.

    This week a team of Russian researchers roped their way down 34 feet to the bottom of the largest crater and found no evidence of alien beings or meteorites that some people had offered up as possible explanations.

    We managed to go down into the funnel, all was successful,” Vladimir Pushkarev, director of the Russian Center of Arctic Exploration and the leader of the team, told The Siberian Times. “We took all the probes we planned, and made measurements. Now scientists need time to process all the data and only then can they draw conclusions.”

    Scroll down for photos.

    So what did cause the holes to form? According to Pushkarev, the leading theory is that the holes were created by pockets of gas that exploded underground.

    “As of now we don’t see anything dangerous in the sudden appearance of such holes,” he told The Siberian Times, “but we’ve got to study them properly to make absolutely sure we understand the nature of their appearance and don’t need to be afraid about them.”

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

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    Vladimir Pushkarev/The Siberian Times

    See the full article here.

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  • richardmitnick 11:01 am on November 9, 2014 Permalink | Reply
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    From livescience: “Crater Hunters Find New Clues to Ancient Impact Storm” 

    Livescience

    October 31, 2014
    Becky Oskin

    Back when Wisconsin and western Russia once shared an address south of the equator, a violent collision in the asteroid belt blasted Earth with meteorites.

    hole
    A meteor crater in northern Quebec, Canada.
    Credit: NASA Earth Observatory

    The space rock smashup showered Earth with up to 100 times more meteorites than today’s rate (a rock the size of a football field hits the planet about every 10,000 years). Yet, only a dozen or so impact craters have been found from the ancient bombardment 470 million years ago, during the Ordovician Period. Most are in North America, Sweden and western Russia. There are only about 185 known impact craters on Earth of any age, while the moon has more than 100,000.

    But the number of Ordovician craters may soon take off. That’s because it’s easier and cheaper than ever to hunt down evidence that confirms an impact. The clinchers include shocked minerals, deformed rocks and structural features that match other craters.

    “Google Earth images are not good enough to identify an impact structure,” noted planetary geologist Christian Köeberl on Oct. 22, at the Geological Society of America’s annual meeting in Vancouver, British Columbia. During the Vancouver meeting, researchers presented new clues that bring suspected craters in Wisconsin, Kentucky and Tennessee closer to official listings as Ordovician impact craters.

    The three enigmatic structures retain their circular shape, but have lost most of their original features through erosion. In the last century, quarrying has also slowly dismantled the Wisconsin crater. Only the central uplift seems to persist. When a meteorite hits, the impact’s force causes the underlying rock to rebound upward, leaving a topographic high in the center of the crater.

    In each state, researchers looked for traces of minerals shattered or heated by the impact. So far, no one has found one of the smoking guns in crater research: shatter cones, the finely fractured rocks created when the shock wave travels through the ground. The fractures are often arranged in a conical shape, like an ice cream cone.

    Three little craters

    thr
    Fractured rocks exposed in a quarry in Brussels Hill, Wisconsin. Credit: Emily Zawacki

    But even without a smoking gun, at Brussels Hill in Door County, Wisconsin, a meteorite impact is the best explanation for the perfectly round, 130-foot-tall (40 meters) hill, said Emily Zawacki, an undergraduate at Lawrence University in Appleton, Wisconsin. The flat-topped peak is filled with fractured blocks of Cambrian sandstone that should lie some 1,300 feet below the younger carbonate rocks. The fragmented rocks all tilt toward the center of the hill, and a series of faults radiate outward from its center.

    The evidence all points to a deeply eroded impact crater, Zawacki said. “This is a highly disturbed area in otherwise flat-lying stratigraphy,” Zawacki said. “It very clearly is anomalous and we feel a meteoritic impact best explains it.”

    In the middle of Tennessee, the Howell Structure has confounded geologists for decades. The bowl-shaped basin is about the same diameter as Brussels Hill (about 1.2 miles, or 2 km). In this case, however, the suspected crater is weaker than the surrounding rocks, creating a depression. A pile of fragmented carbonate and other craterlike features suggests an impact origin.

    Keith Milam, a professor at Ohio University in Athens, recently uncovered a rare trove of rock cores drilled at Howell in the 1960s. John Bensko, a retired lunar geologist from NASA’s Marshall Space Flight Center, provided the 15 segments. Bensko oversaw the testing of drilling equipment intended for the canceled Apollo 18 program. The first tests on the rock cores suggest the fragmented carbonate rocks were shocked by a meteorite impact, Milam reported at the Vancouver meeting.

    Finally, the Jeptha Knob structure in Kentucky is a site that stands out on Google Earth and just needs the right mineral evidence to certify its impact origin. “I don’t think you can say for sure this is an impact structure yet,” said Eric Gibbs, an undergraduate at Ohio University in Athens. Gibbs is testing the X-ray diffraction pattern produced by minerals from the crater. The pattern shortens and widens with increasing shock, he said.

    ord
    A partial map of Ordovician continents and impact craters. Credit: Jens Ormö et al., Scientific Reports

    The initial tests, presented at the Vancouver geology meeting, support an impact origin for the hill. Jeptha Knob is the highest point in Kentucky’s Bluegrass Region, rising some 300 feet (90 m) above the surrounding farms. The round crater is ringed by faults and busted-up Ordovician limestone, but topped by flat layers of younger carbonate rocks.

    The apparent alignment of many of these craters makes it seem that some coincidence favored Earth’s tropical latitudes during the big Ordovician bombardment.

    At the time, North America was flipped backward and sitting across the equator. The Baltica continent — western Russia, Sweden and Finland — was just to the south. There are six confirmed Ordovician craters in the central United States and more in the middle of Canada. There are five confirmed craters in Sweden; and this month a double crater was identified in central Sweden at Lockne and Malinga, according to a study published Oct. 24 in the journal Scientific Reports. Who knows how many more are buried under the protective limestones and shales of the huge Ordovician seas?

    See the full article, with additional material, here.

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  • richardmitnick 2:23 pm on November 7, 2014 Permalink | Reply
    Tags: , , , Geochemistry, Geology   

    From Caltech: “Unexpected Findings Change the Picture of Sulfur on the Early Earth” 

    Caltech Logo
    Caltech

    11/07/2014
    Kimm Fesenmaier

    Scientists believe that until about 2.4 billion years ago there was little oxygen in the atmosphere—an idea that has important implications for the evolution of life on Earth. Evidence in support of this hypothesis comes from studies of sulfur isotopes preserved in the rock record. But the sulfur isotope story has been uncertain because of the lack of key information that has now been provided by a new analytical technique developed by a team of Caltech geologists and geochemists. The story that new information reveals, however, is not what most scientists had expected.

    slope
    2.5 billion-year-old sedimentary strata exposed in the Northern Cape Province of South Africa. Credit: Jess Adkins/Caltech

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    Reef mounds formed of radiating calcium carbonate crystal fans on the Archean seafloor. Credit: Jess Adkins/Caltech

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    Cross-section view of calcium carbonate crystal fans that grew on the seafloor circa 2.6 billion years ago. Credit: Jess Adkins/Caltech

    “Our new technique is 1,000 times more sensitive for making sulfur isotope measurements,” says Jess Adkins, professor of geochemistry and global environmental science at Caltech. “We used it to make measurements of sulfate groups dissolved in carbonate minerals deposited in the ocean more than 2.4 billion years ago, and those measurements show that we have been thinking about this part of the sulfur cycle and sulfur isotopes incorrectly.”

    The team describes their results in the November 7 issue of the journal Science. The lead author on the paper is Guillaume Paris, an assistant research scientist at Caltech.

    Nearly 15 years ago, a team of geochemists led by researchers at UC San Diego discovered there was something peculiar about the sulfur isotope content of rocks from the Archean era, an interval that lasted from 3.8 billion to about 2.4 billion years ago. In those ancient rocks, the geologists were analyzing the abundances of stable isotopes of sulfur.

    When sulfur is involved in a reaction—such as microbial sulfate reduction, a way for microbes to eat organic compounds in the absence of oxygen—its isotopes are usually fractionated, or separated, from one another in proportion to their differences in mass. That is, 34S gets fractionated from 32S about twice as much as 33S gets fractionated from 32S. This process is called mass-dependent fractionation, and, scientists have found that it dominates in virtually all sulfur processes operating on Earth’s surface for the last 2.4 billion years.

    However, in older rocks from the Archean era (i.e., older than 2.4 billion years), the relative abundances of sulfur isotopes do not follow the same mass-related pattern, but instead show relative enrichments or deficiencies of 33S relative to 34S. They are said to be the product of mass-independent fractionation (MIF).

    The widely accepted explanation for the occurrence of MIF is as follows. Billions of years ago, volcanism was extremely active on Earth, and all those volcanoes spewed sulfur dioxide high into the atmosphere. At that time, oxygen existed at very low levels in the atmosphere, and therefore ozone, which is produced when ultraviolet radiation strikes oxygen, was also lacking. Today, ozone prevents ultraviolet light from reaching sulfur dioxide with the energy needed to fractionate sulfur, but on the early Earth, that was not the case, and MIF is the result. Researchers have been able to reproduce this effect in the lab by shining lasers onto sulfur dioxide and producing MIF.

    Geologists have also measured the sulfur isotopic composition of sedimentary rocks dating to the Archean era, and found that sulfides—sulfur-bearing compounds such as pyrite (FeS2)—include more 33S than would be expected based on normal mass-dependent processes. But if those minerals are enriched in 33S, other minerals must be correspondingly lacking in the isotope. According to the leading hypothesis, those 33S-deficient minerals should be sulfates—oxidized sulfur-bearing compounds—that were deposited in the Archean ocean.

    “That idea was put forward on the basis of experiment. To test the hypothesis, you’d need to check the isotope ratios in sulfate salts (minerals such as gypsum), but those don’t really exist in the Archean rock record since there was very little oxygen around,” explains Woody Fischer, professor of geobiology at Caltech and a coauthor on the new paper. “But there are trace amounts of sulfate that got trapped in carbonate minerals in seawater.”

    However, because those sulfates are present in such small amounts, no one has been able to measure well their isotopic composition. But using a device known as a multicollector inductively-coupled mass spectrometer to precisely measure multiple sulfur isotopes, Adkins and his colleague Alex Sessions, a professor of geobiology, developed a method that is sensitive enough to measure the isotopic composition of about 10 nanomoles of sulfate in just a few tens of milligrams of carbonate material.

    The authors used the method to measure the sulfate content of carbonates from an ancient carbonate platform preserved in present-day South Africa, an ancient version of the depositional environments found in the Bahamas today. Analyzing the samples, which spanned 70 million years and a variety of marine environments, the researchers found exactly the opposite of what had been predicted: the sulfates were actually enriched by 33S rather than lacking in it.

    “Now, finally, we’re looking at this sulfur cycle and the sulfur isotopes correctly,” Adkins says.

    What does this mean for the atmospheric conditions of the early Earth? “Our findings underscore that the oxygen concentrations in the early atmosphere could have been incredibly low,” Fischer says.

    Knowledge of sulfate isotopes changes how we understand the role of biology in the sulfur cycle, he adds. Indeed, the fact that the sulfates from this time period have the same isotopic composition as sulfide minerals suggests that the sulfides may be the product of microbial processes that reduced seawater sulfate to sulfide (which later precipitated in sediments in the form of pyrite). Previously, scientists thought that all of the isotope fractionation could be explained by inorganic processes alone.

    In a second paper also in the November 7 issue of Science, Paris, Adkins, Sessions, and colleagues from a number of institutions around the world report on related work in which they measured the sulfates in Indonesia’s Lake Matano, a low-sulfate analog of the Archean ocean.

    At about 100 meters depth, the bacterial communities in Lake Matano begin consuming sulfate rather than oxygen, as do most microbial communities, yielding sulfide. The researchers measured the sulfur isotopes within the sulfates and sulfides in the lake water and sediments and found that despite the low concentrations of sulfate, a lot of mass-dependent fractionation was taking place. The researchers used the data to build a model of the lake’s sulfur cycle that could produce the measured fractionation, and when they applied their model to constrain the range of concentrations of sulfate in the Archean ocean, they found that the concentration was likely less than 2.5 micromolar, 10,000 times lower than the modern ocean.

    “At such low concentration, all the isotopic variability starts to fit,” says Adkins. “With these two papers, we were able to come at the same problem in two ways—by measuring the rocks dating from the Archean and by looking at a model system today that doesn’t have much sulfate—and they point toward the same answer: the sulfate concentration was very low in the Archean ocean.”

    Samuel M. Webb of the Stanford Synchrotron Radiation Lightsource is also an author on the paper, “Neoarchean carbonate-associated sulfate records positive Δ33S anomalies.” The work was supported by funding from the National Science Foundation’s Division of Earth Sciences, the Henry and Camille Dreyfus Foundation’s Postdoctoral Program in Environmental Chemistry, and the David and Lucile Packard Foundation.

    Paris is also a co-lead author on the second paper, Sulfate was a trace constituent of Archean seawater. Additional authors on that paper are Sean Crowe and CarriAyne Jones of the University of British Columbia and the University of Southern Denmark; Sergei Katsev of the University of Minnesota Duluth; Sang-Tae Kim of McMaster University; Aubrey Zerkle of the University of St. Andrews; Sulung Nomosatryo of the Indonesian Institute of Sciences; David Fowle of the University of Kansas; James Farquhar of the University of Maryland, College Park; and Donald Canfield of the University of Southern Denmark. Funding was provided by an Agouron Institute Geobiology Fellowship and a Natural Sciences and Engineering Research Council of Canada Postdoctoral Fellowship, as well as by the Danish National Research Foundation and the European Research Council.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 7:20 pm on November 3, 2014 Permalink | Reply
    Tags: , Geology,   

    From livescience: “Rare Mineral Discovered in Ancient Meteorite Impact Crater” 

    Livescience

    November 03, 2014
    Becky Oskin

    A rare mineral known from just three massive meteorite impacts has now turned up in a Wisconsin crater.

    Researchers discovered the mineral, called reidite, at the Rock Elm impact structure in western Wisconsin. Reidite is a dense form of zircon, one of the hardiest minerals on Earth.

    This is the oldest reidite ever found,, said Aaron Cavosie, a geochemist at the University of Puerto Rico in Mayagüez. The Rock Elm meteorite crater is 450 million to 470 million years old, he said.

    Scientists first discovered the unusual high-pressure zircon in a laboratory in the 1960s. Reidite was finally identified in nature starting in 2001, at three impact sites: the Chesapeake Bay Crater in Virginia, Ries Crater in Germany and Xiuyan Crater in China.

    The reidite was an utterly unexpected find for Cavosie, who was collecting zircons to establish a more precise impact age for the Rock Elm crater. “No one in their right mind would have looked for reidite in sandstone,” he told Live Science. The Rock Elm crater was gouged out of carbonate rocks and sandstone that contains tiny fragments of quartz and zircon. The earlier reidite discoveries were all in impact melt breccias — a mix of rock that melted and cooled into glass during the impact and unmelted rock fragments. [Crash! The 10 Biggest Impact Craters on Earth]

    “I work with the oldest zircons on Earth, and reidite is so much rarer than 4.4-billion-year-old zircons,” said Cavosie, who presented the results of the research Oct. 22 at the Geological Society of America’s annual meeting in Vancouver, British Columbia.

    reidite
    The rare mineral reidite was discovered in Wisconsin’s Rock Elm Crater Credit: Aaron Cavosie

    Zircon morphs into reidite when shock waves from meteorite impacts hike up pressures and temperatures to extreme levels, equal to those deep inside the Earth where diamonds form. The pressure makes minerals tightly repack their molecules into denser crystal structures. Reidite has the same composition as regular zircon but is about 10 percent denser.

    The specks of reidite Cavosie spotted are smaller than the diameter of a human hair and are scattered within “shocked” zircons that were fractured during the Rock Elm impact. But each mineral reflects light differently, which caught Cavosie’s eye as he examined slices of rock under a powerful microscope. Working with colleagues in Australia, Cavosie confirmed the presence of reidite by zapping the tiny zircons with electrons. Every mineral scatters electrons in a unique way, and the tests confirmed the presence of reidite, Cavosie announced in Vancouver.

    “This is a cool find in the realm of high-pressure metamorphism,” Cavosie said.

    It takes incredible pressure to transform zircon into reidite, so the mineral’s presence means the Rock Elm crater underwent much higher shock pressures than originally thought, Cavosie said. The transition to reidite takes place anywhere between 30 and 80 gigapascals. Earlier pressure estimates from the crater’s shocked quartz topped out at 10 gigapascals, according to previous studies.

    Any impact crater carved from sandstone will also have zircon, and Cavosie now thinks reidite is likely more common than scientists previously thought. “It’s now time to look for it where we never would have anticipated finding it,” he said.

    See the full article here.

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  • richardmitnick 1:46 pm on November 2, 2014 Permalink | Reply
    Tags: , , , Geology   

    From astrobio.net: “Lack of oxygen delayed the rise of animals on Earth” 

    Astrobiology Magazine

    Astrobiology Magazine

    Nov 2, 2014
    No Writer Credit

    Geologists are letting the air out of a nagging mystery about the development of animal life on Earth.

    Scientists have long speculated as to why animal species didn’t flourish sooner, once sufficient oxygen covered the Earth’s surface. Animals began to prosper at the end of the Proterozoic period, about 800 million years ago — but what about the billion-year stretch before that, when most researchers think there also was plenty of oxygen?

    Well, it seems the air wasn’t so great then, after all.

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    Christopher Reinhard and Noah Planavsky conduct research for the study in China. Credit: Yale University

    In a study published Oct. 30 in Science, Yale researcher Noah Planavsky and his colleagues found that oxygen levels during the “boring billion” period were only 0.1% of what they are today. In other words, Earth’s atmosphere couldn’t have supported a diversity of creatures, no matter what genetic advancements were poised to occur.

    “There is no question that genetic and ecological innovation must ultimately be behind the rise of animals, but it is equally unavoidable that animals need a certain level of oxygen,” said Planavsky, co-lead author of the research along with Christopher Reinhard of the Georgia Institute of Technology. “We’re providing the first evidence that oxygen levels were low enough during this period to potentially prevent the rise of animals.”

    The scientists found their evidence by analyzing chromium (Cr) isotopes in ancient sediments from China, Australia, Canada, and the United States. Chromium is found in the Earth’s continental crust, and chromium oxidation is directly linked to the presence of free oxygen in the atmosphere.

    Specifically, the team studied samples deposited in shallow, iron-rich ocean areas, near the shore. They compared their data with other samples taken from younger locales known to have higher levels of oxygen.

    Oxygen’s role in controlling the first appearance of animals has long vexed scientists. “We were missing the right approach until now,” Planavsky said. “Chromium gave us the proxy.” Previous estimates put the oxygen level at 40% of today’s conditions during pre-animal times, leaving open the possibility that oxygen was already plentiful enough to support animal life.

    In the new study, the researchers acknowledged that oxygen levels were “highly dynamic” in the early atmosphere, with the potential for occasional spikes. However, they said, “It seems clear that there is a first-order difference in the nature of Earth surface Cr cycling” before and after the rise of animals.

    “If we are right, our results will really change how people view the origins of animals and other complex life, and their relationships to the co-evolving environment,” said co-author Tim Lyons of the University of California-Riverside. “This could be a game changer.”

    “There’s a lot of interest right now in a broader discussion surrounding the role that environmental stability played in the evolution of complex life, and we think our results are a significant contribution to that,” Reinhard said.

    See the full article here.

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  • richardmitnick 3:24 pm on October 25, 2014 Permalink | Reply
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    From livesience: “Telltale Signs of Life Could Be Deepest Yet” 

    Livescience

    October 24, 2014
    Becky Oskin

    Telltale signs of life have been discovered in rocks that were once 12 miles (20 kilometers) below Earth’s surface — some of the deepest chemical evidence for life ever found.

    life
    White aragonite veins on Washington’s San Juan Islands may contain evidence of deep microbial life.
    Credit: Philippa Stoddard

    Researchers found carbon isotopes in rocks on Washington state’s South Lopez Island that suggest the minerals grew from fluids flush with microbial methane. Methane from living creatures has distinct levels of carbon isotopes that distinguish it from methane gas that arises from rocks. (Isotopes are atoms of the same element with different numbers of neutrons in their nuclei.)

    In a calcium carbonate mineral called aragonite, the standard mix of carbon isotopes was radically shifted toward lighter carbon isotopes (by about 50 per mil, or parts per thousand). This ratio is characteristic of methane gas made by microorganisms, said Philippa Stoddard, an undergraduate student at Yale University who presented the research Tuesday (Oct. 21) at the Geological Society of America‘s annual meeting in Vancouver, British Columbia. “These really light signals are only observed when you have biological processes,” she told Live Science.

    The pale aragonite veins cut through basalt rocks that sat offshore North America millions of years ago. The veins formed after the basalt was sucked into an ancient subduction zone, one that predated today’s Cascadia subduction zone. Two tectonic plates smash together at subduction zones, and one plate descends under the other, creating deep trenches.

    Methane gas supplied the carbon as aragonite crystallized in cracks in the basalt, and replaced pre-existing limestone. The researchers think that microbes produced the methane gas as a waste product.

    “We reason that you could have life deeper in subduction zones, because you have a lot of water embedded in those rocks, and the rocks stay cold longer as the [plate] comes down,” Stoddard said.

    But the South Lopez Island aragonite suggests the minerals formed under extreme conditions that push the limits of life on Earth. For example, temperatures reached more than 250 degrees Fahrenheit (122 degrees Celsius), above the stability limit for DNA, Stoddard said. However, the researchers think the higher pressures at these depths may have counterbalanced the effects of the heat. The rocks are now visible thanks to faulting, which pushed them back up to the surface.

    Stoddard and her collaborators plan to sample more of the aragonite and other rocks nearby, to gain a better understanding of where the fluids came from and pin down the temperatures at which the rocks formed.

    Methane seeps teeming with million of microbes are found on the seafloor offshore Washington and Oregon along the Cascadia subduction zone. And multicellular life has been documented in the Mariana Trench, the deepest spot on Earth, and in South African mines 0.8 miles (1.3 km) deep. Researchers also have discovered microbes feasting on rocks within the oceanic crust itself.

    See the full article here.

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  • richardmitnick 4:19 pm on October 21, 2014 Permalink | Reply
    Tags: , , Geology, USGS   

    From livescience: “Earthquake Forecast: 4 California Faults Are Ready to Rupture” 

    Livescience

    October 13, 2014
    Becky Oskin

    With several faults slicing through the San Francisco Bay Area, forecasting the next deadly earthquake becomes a question of when and where, not if.

    Now researchers propose that four faults have built up enough seismic strain (stored energy) to unleash destructive earthquakes, according to a study published today (Oct. 13) in the Bulletin of the Seismological Society of America.

    The quartet includes the Hayward Fault, the Rodgers Creek Fault, the Green Valley Fault and the Calaveras Fault. While all are smaller pieces of California’s San Andreas Fault system, which is more than 800 miles (1,300 kilometers) long, the four faults are a serious threat because they directly underlie cities. [Photo Journal: The Gorgeous San Andreas Fault]

    fault
    San Francisco Bay Area earthquake faults are drawn in red.

    saf
    Description: USGS diagram of San Andreas Fault
    Date: 14 March 2006

    “The Hayward Fault is just right in the heart of where people live, and the most buildings and the most infrastructure,” said Jim Lienkaemper, lead study author and a research geophysicist at the U.S. Geological Survey’s Earthquake Science Center in Menlo Park, California. “But it’s not just one fault, it’s the whole shopping basket. If you are in the middle of the Bay Area, you are near a whole lot of faults, and I’m concerned about all of them.”

    Lienkaemper and his colleagues gauged the potential for destructive earthquakes by monitoring tiny surface shifts along California faults. Certain faults are in constant motion, creeping steadily by less than 0.4 inches (1 centimeter) each year. These slow movements add up over time, cracking sidewalk curbs and buildings. They also serve as clues to what’s happening deep below ground, where earthquakes strike.

    “If you figure out where faults are creeping, it tells you where they’re locked and how much they’re locked,” Lienkaemper told Live Science.

    Fault creep varies, with some faults sliding at a snail’s pace and others barely budging. Models suggest that the diversity comes from locked zones that are 3 to 6 miles (5 to 10 km) below the surface, where the fault is stuck instead of sliding. For example, the relatively fast-creeping southern Hayward Fault is only about 40 percent locked, on average, while the slow-creeping Rodgers Creek Fault is 89 percent locked, the study reports. When these locked areas build up a critical amount of strain, they break apart in an earthquake.
    earthquakes

    sfa
    Map of Bay Area earthquake faults and creep measurement sites.
    Credit: USGS

    Lienkaemper and his co-author estimated a fault’s future earthquake potential by combining creep measurements with mathematical fault models and other regional data, such as the time since the last earthquake.

    The Hayward Fault has banked enough energy for a magnitude-6.8 earthquake, according to the study. The Rodgers Creek Fault could trigger a magnitude-7.1 earthquake, and the Green Valley Fault also has the potential to unleash a magnitude-7.1 shaker. The Northern Calaveras Fault is set for a magnitude-6.8 temblor.

    Of all Bay Area faults, the Hayward Fault is most likely to spawn a damaging earthquake in the next 30 years, scientists think. Its 1868 earthquake was called the Big One until the great 1906 San Francisco quake came along. The Hayward Fault has ruptured about every 140 years for its previous five large earthquakes. The probability of a magnitude-6.7 earthquake on the Hayward Fault is 30 percent in the next 30 years.

    Though 146 years have now passed since the last Hayward earthquake, that doesn’t mean the fault is overdue for another quake, Lienkaemper said. “The average is 160 years, but the uncertainty is plus or minus 100 years, which is almost as big as the time [interval] itself.” The 160-year average comes from an analysis of data collected from trenches dug across the fault that revealed evidence of earthquakes over thousands of years.

    The Rodgers Creek and Green Valley Faults are also closing in on their average repeat times between earthquakes.

    See the full article here.

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  • richardmitnick 3:51 pm on October 16, 2014 Permalink | Reply
    Tags: , Geology,   

    From UC Berkeley: “Earth’s magnetic field could flip within a human lifetime” 

    UC Berkeley

    UC Berkeley

    October 14, 2014
    Robert Sanders

    Imagine the world waking up one morning to discover that all compasses pointed south instead of north.

    It’s not as bizarre as it sounds. Earth’s magnetic field has flipped – though not overnight – many times throughout the planet’s history. Its dipole magnetic field, like that of a bar magnet, remains about the same intensity for thousands to millions of years, but for incompletely known reasons it occasionally weakens and, presumably over a few thousand years, reverses direction.

    team
    Left to right, Biaggio Giaccio, Gianluca Sotilli, Courtney Sprain and Sebastien Nomade sitting next to an outcrop in the Sulmona basin of the Apennine Mountains that contains the Matuyama-Brunhes magnetic reversal. A layer of volcanic ash interbedded with the lake sediments can be seen above their heads. Sotilli and Sprain are pointing to the sediment layer in which the magnetic reversal occurred. (Photo by Paul Renne)

    Now, a new study by a team of scientists from Italy, France, Columbia University and the University of California, Berkeley, demonstrates that the last magnetic reversal 786,000 years ago actually happened very quickly, in less than 100 years – roughly a human lifetime.

    “It’s amazing how rapidly we see that reversal,” said UC Berkeley graduate student Courtney Sprain. “The paleomagnetic data are very well done. This is one of the best records we have so far of what happens during a reversal and how quickly these reversals can happen.”

    Sprain and Paul Renne, director of the Berkeley Geochronology Center and a UC Berkeley professor-in- residence of earth and planetary science, are coauthors of the study, which will be published in the November issue of Geophysical Journal International and is now available online.

    Flip could affect electrical grid, cancer rates

    The discovery comes as new evidence indicates that the intensity of Earth’s magnetic field is decreasing 10 times faster than normal, leading some geophysicists to predict a reversal within a few thousand years.

    Though a magnetic reversal is a major planet-wide event driven by convection in Earth’s iron core, there are no documented catastrophes associated with past reversals, despite much searching in the geologic and biologic record. Today, however, such a reversal could potentially wreak havoc with our electrical grid, generating currents that might take it down.

    And since Earth’s magnetic field protects life from energetic particles from the sun and cosmic rays, both of which can cause genetic mutations, a weakening or temporary loss of the field before a permanent reversal could increase cancer rates. The danger to life would be even greater if flips were preceded by long periods of unstable magnetic behavior.

    “We should be thinking more about what the biologic effects would be,” Renne said.

    Dating ash deposits from windward volcanoes

    The new finding is based on measurements of the magnetic field alignment in layers of ancient lake sediments now exposed in the Sulmona basin of the Apennine Mountains east of Rome, Italy. The lake sediments are interbedded with ash layers erupted from the Roman volcanic province, a large area of volcanoes upwind of the former lake that includes periodically erupting volcanoes near Sabatini, Vesuvius and the Alban Hills.

    two
    Leonardo Sagnotti, standing, and coauthor Giancarlo Scardia collecting a sample for paleomagnetic analysis.

    Italian researchers led by Leonardo Sagnotti of Rome’s National Institute of Geophysics and Volcanology measured the magnetic field directions frozen into the sediments as they accumulated at the bottom of the ancient lake.

    Sprain and Renne used argon-argon dating, a method widely used to determine the ages of rocks, whether they’re thousands or billions of years old, to determine the age of ash layers above and below the sediment layer recording the last reversal. These dates were confirmed by their colleague and former UC Berkeley postdoctoral fellow Sebastien Nomade of the Laboratory of Environmental and Climate Sciences in Gif-Sur-Yvette, France.

    Because the lake sediments were deposited at a high and steady rate over a 10,000-year period, the team was able to interpolate the date of the layer showing the magnetic reversal, called the Matuyama-Brunhes transition, at approximately 786,000 years ago. This date is far more precise than that from previous studies, which placed the reversal between 770,000 and 795,000 years ago.

    “What’s incredible is that you go from reverse polarity to a field that is normal with essentially nothing in between, which means it had to have happened very quickly, probably in less than 100 years,” said Renne. “We don’t know whether the next reversal will occur as suddenly as this one did, but we also don’t know that it won’t.”

    Unstable magnetic field preceded 180-degree flip

    Whether or not the new finding spells trouble for modern civilization, it likely will help researchers understand how and why Earth’s magnetic field episodically reverses polarity, Renne said.
    the polar wanderingsThe ‘north pole’ — that is, the direction of magnetic north — was reversed a million years ago. This map shows how, starting about 789,000 years ago, the north pole wandered around Antarctica for several thousand years before flipping 786,000 years ago to the orientation we know today, with the pole somewhere in the Arctic.

    The magnetic record the Italian-led team obtained shows that the sudden 180-degree flip of the field was preceded by a period of instability that spanned more than 6,000 years. The instability included two intervals of low magnetic field strength that lasted about 2,000 years each. Rapid changes in field orientations may have occurred within the first interval of low strength. The full magnetic polarity reversal – that is, the final and very rapid flip to what the field is today – happened toward the end of the most recent interval of low field strength.

    Renne is continuing his collaboration with the Italian-French team to correlate the lake record with past climate change.

    Renne and Sprain’s work at the Berkeley Geochronology Center was supported by the Ann and Gordon Getty Foundation.

    See the full article here.

    Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

    UC Berkeley Seal

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  • richardmitnick 3:43 pm on September 19, 2014 Permalink | Reply
    Tags: , , Geology,   

    From astrobio.net: “What set the Earth’s plates in motion?” 

    Astrobiology Magazine

    Astrobiology Magazine

    Sep 19, 2014
    Source: University of Sidney

    The mystery of what kick-started the motion of our earth’s massive tectonic plates across its surface has been explained by researchers at the University of Sydney.

    “Earth is the only planet in our solar system where the process of plate tectonics occurs,” said Professor Patrice Rey, from the University of Sydney’s School of Geosciences.

    “The geological record suggests that until three billion years ago the earth’s crust was immobile so what sparked this unique phenomenon has fascinated geoscientists for decades. We suggest it was triggered by the spreading of early continents then eventually became a self-sustaining process.”

    Professor Rey is lead author of an article on the findings published in Nature on Wednesday, 17 September.

    The other authors on the paper are Nicolas Flament, also from the School of Geosciences and Nicolas Coltice, from the University of Lyon.

    split
    The image shows a snapshot from the film after 45 million years of spreading. The pink is the region where the mantle underneath the early continent has melted, facilitating its spreading, and the initiation of the plate tectonic process. Credit: Patrice Rey, Nicolas Flament and Nicolas Coltice.

    The image shows a snapshot after 45 million years of spreading. The pink is the region where the mantle underneath the early continent has melted, facilitating its spreading, and the initiation of the plate tectonic process. Credit: Patrice Rey, Nicolas Flament and Nicolas Coltice.

    There are eight major tectonic plates that move above the earth’s mantle at rates up to 150 millimetres every year.

    In simple terms the process involves plates being dragged into the mantle at certain points and moving away from each other at others, in what has been dubbed ‘the conveyor belt’.

    Plate tectonics depends on the inverse relationship between density of rocks and temperature.

    At mid-oceanic ridges, rocks are hot and their density is low, making them buoyant or more able to float. As they move away from those ridges they cool down and their density increases until, where they become denser than the underlying hot mantle, they sink and are ‘dragged’ under.

    ridge
    Mid-ocean ridge

    But three to four billion years ago, the earth’s interior was hotter, volcanic activity was more prominent and tectonic plates did not become cold and dense enough to spontaneously sank.

    “So the driving engine for plate tectonics didn’t exist,” said Professor Rey said.

    “Instead, thick and buoyant early continents erupted in the middle of immobile plates. Our modelling shows that these early continents could have placed major stress on the surrounding plates. Because they were buoyant they spread horizontally, forcing adjacent plates to be pushed under at their edges.”

    “This spreading of the early continents could have produced intermittent episodes of plate tectonics until, as the earth’s interior cooled and its crust and plate mantle became heavier, plate tectonics became a self-sustaining process which has never ceased and has shaped the face of our modern planet.”

    The new model also makes a number of predictions explaining features that have long puzzled the geoscience community.

    See the full article here.

    NASA

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