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  • richardmitnick 8:37 am on June 23, 2016 Permalink | Reply
    Tags: , , , Geology,   

    From JPL-Caltech: “NASA Scientists Discover Unexpected Mineral on Mars” 

    NASA JPL Banner

    JPL-Caltech

    June 22, 2016
    Guy Webster
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-6278
    guy.webster@jpl.nasa.gov

    William P. Jeffs
    Johnson Space Center, Houston
    281-483-5111
    william.p.jeffs@nasa.gov

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    This low-angle self-portrait of NASA’s Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called “Buckskin.” Bright powder from that July 30, 2015, drilling is visible in the foreground. Credit: NASA/JPL-Caltech/MSSS

    Scientists have discovered an unexpected mineral in a rock sample at Gale Crater on Mars, a finding that may alter our understanding of how the planet evolved.

    NASA’s Mars Science Laboratory rover, Curiosity, has been exploring sedimentary rocks within Gale Crater since landing in August 2012. In July 2015, on Sol 1060 (the number of Martian days since landing), the rover collected powder drilled from rock at a location named “Buckskin.” Analyzing data from an X-ray diffraction instrument on the rover that identifies minerals, scientists detected significant amounts of a silica mineral called tridymite.

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    A common form of Tridymite, ultra thin colorless tabulars (image width: 1,1 mm) – Locality: Wannenköpfe, Ochtendung, Eifel region, Germany 2005

    This detection was a surprise to the scientists, because tridymite is generally associated with silicic volcanism, which is known on Earth but was not thought to be important or even present on Mars.

    The discovery of tridymite might induce scientists to rethink the volcanic history of Mars, suggesting that the planet once had explosive volcanoes that led to the presence of the mineral.

    Scientists in the Astromaterials Research and Exploration Science (ARES) Division at NASA’s Johnson Space Center in Houston led the study. A paper on the team’s findings has been published in the Proceedings of the National Academy of Sciences.

    “On Earth, tridymite is formed at high temperatures in an explosive process called silicic volcanism. Mount St. Helens, the active volcano in Washington State, and the Satsuma-Iwojima volcano in Japan are examples of such volcanoes. The combination of high silica content and extremely high temperatures in the volcanoes creates tridymite,” said Richard Morris, NASA planetary scientist at Johnson and lead author of the paper. “The tridymite was incorporated into ‘Lake Gale’ mudstone at Buckskin as sediment from erosion of silicic volcanic rocks.”

    The paper also will stimulate scientists to re-examine the way tridymite forms. The authors examined terrestrial evidence that tridymite could form at low temperatures from geologically reasonable processes and not imply silicic volcanism. They found none. Researchers will need to look for ways that it could form at lower temperatures.

    “I always tell fellow planetary scientists to expect the unexpected on Mars,” said Doug Ming, ARES chief scientist at Johnson and co-author of the paper. “The discovery of tridymite was completely unexpected. This discovery now begs the question of whether Mars experienced a much more violent and explosive volcanic history during the early evolution of the planet than previously thought.”

    To view the paper, go to:

    http://www.pnas.org/content/early/2016/06/07/1607098113.full

    To learn more about the ARES Division, go to:

    http://ares.jsc.nasa.gov/aboutares/index.cfm

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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

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  • richardmitnick 9:16 am on June 22, 2016 Permalink | Reply
    Tags: , , Geology, , Traces of Ancient Buried Subduction Zone Found in China   

    From Eos: “Traces of Ancient Buried Subduction Zone Found in China” 

    Eos news bloc

    Eos

    6.22.16
    Lily Strelich

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    The Devil City, a wind erosion landform near the town of Urho in the western Junggar region of northwestern China. Deep below this landscape and surrounding areas lie remnants of an ancient subduction zone, researchers report. Credit: Yixian Xu

    Practically every geological feature on the face of the Earth is a result of the steady movement of tectonic plates. Mammoth slabs of oceanic and continental crust jostle and leapfrog each other, and the traces of these plate motions are sometimes preserved in the rock record. Reconstructing the history of tectonic plate movement is essential to better understand the history of the planet.

    However, identifying ancient subduction zones remains a challenge because scientists rarely see traces of collisions between oceanic slabs and continental crust. Now Xu et al. have found new evidence of a fossil intraoceanic subduction zone in northwest China.

    The team focused on the geology of the Darbut belt, a part of the western Junggar region of northwest China, and collected magnetotelluric data using 60 broadband stations located along a 182-kilometer stretch running northwest to southeast. This technique allows scientists to measure the electrical conductivity of geological materials and recognize features of both modern and fossil subduction zones—for example, spotting a resistive oceanic plate under conductive oceanic upper mantle.

    Using this method, the researchers were able to obtain a resistivity model of the area, which they interpreted alongside geological and geophysical observational data, mineral physics experiments, and geodynamic modeling from previous studies.

    Hidden beneath the accretionary layers of the western Junggar basin, they spotted the remains of a late Carboniferous intraoceanic subduction system. It is similar to a modern intraoceanic convergent boundary and unusually well preserved—no major tectonic events took place in the millennia since to destroy these geologic features. The authors believe this discovery provides valuable insight into the formation of collision belts and the potential exploration of mineral resources in the area. (Journal of Geophysical Research: Solid Earth, doi:10.1002/2015JB012394, 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 4:00 pm on June 15, 2016 Permalink | Reply
    Tags: , , Geology, New Type of Meteorite Linked to Ancient Asteroid Collision,   

    From UC Davis: “New Type of Meteorite Linked to Ancient Asteroid Collision” 

    UC Davis bloc

    UC Davis

    June 15, 2016
    Becky Oskin

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    The black, grainy meteorite embedded in rock from a Swedish quarry fell to Earth 470 million years ago. Chemically distinct from any meteorite yet discovered, it is likely debris from a massive collision in the asteroid belt. (Qing-zhu Yin, UC Davis).

    An ancient space rock discovered in a Swedish quarry is a type of meteorite never before found on Earth, scientists reported June 14 in the journal Nature Communications.

    “In our entire civilization, we have collected over 50,000 meteorites, and no one has seen anything like this one before,” said study co-author Qing-zhu Yin, professor of geochemistry and planetary sciences at the University of California, Davis. “Discovering a new type of meteorite is very, very exciting.”

    The new meteorite, called Ost 65, appears to be from the missing partner in a massive asteroid collision 470 million years ago. The collision sent debris falling to Earth over about a million years and may have influenced a great diversification of life in the Ordovician Period. One of the objects involved in this collision is well-known: It was the source of L-chondrites, still the most common type of meteorite. But the identity of the object that hit it has been a mystery.

    Ost 65 was discovered in Sweden’s Thorsberg quarry, source of more than 100 fossil meteorites. Measuring just under 4 inches wide, it looks like a gray cow patty plopped into a pristine layer of fossil-rich pink limestone. The Ost 65 rock is called a fossil meteorite because the original rock is almost completely altered except for a few hardy minerals — spinels and chromite. Analyses of chromium and oxygen isotopes in the surviving minerals allowed the researchers to conclude the Ost 65 meteorite is chemically distinct from all known meteorite types.

    By measuring how long Ost 65 was exposed to cosmic rays, the team established that it traveled in space for about a million years before it fell to Earth 470 million years ago. This timeline matches up with L-chondrite meteorites found in the quarry, leading the study authors to suggest the rock is a fragment of the other object from the Ordovician collision. The original object may have been destroyed during the collision, but it’s also possible that the remains are still out in space.

    Meteorites may have influenced evolution

    Researchers think that about 100 times as many meteorites slammed into Earth during the Ordovician compared with today, thanks to the massive collision in the asteroid belt. This rain of meteorites may have opened new environmental niches for organisms, thus boosting both the diversity and complexity of life on Earth.

    “I think this shows the interconnectedness of the entire solar system in space and time, that a random collision 470 million years ago in the asteroid belt could dictate the evolutionary path of species here on Earth,” Yin said.

    The study was led by Birger Schmitz, of Lund University in Sweden. Yin, of UC Davis, together with his postdoctoral fellow Matthew Sanborn, made the very precise measurement of chromium in tiny mineral grains within the meteorite. Researchers from the University of Hawaii at Manoa analyzed its oxygen isotopes.

    The new findings strengthen suspicions that more recent meteorite falls on Earth do not represent the full range of rocks drifting through the solar system. Yin said there is potential to better understand the history of our solar system by collecting meteorite fragments preserved in Earth’s ancient rocks. “If we can go back even further in time, we may eventually be able to find some of the true building blocks of Earth,” Yin said.

    The research was funded by NASA, the UC Office of the President and a European Research Council Advanced Grant.

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    UC Davis Campus

    The University of California, Davis, is a major public research university located in Davis, California, just west of Sacramento. It encompasses 5,300 acres of land, making it the second largest UC campus in terms of land ownership, after UC Merced.

     
  • richardmitnick 10:06 am on June 12, 2016 Permalink | Reply
    Tags: Antarctica, , Geology,   

    From U Colorado: “Antarctic lakes provide glimpse of ancient forest fires” 

    U Colorado

    University of Colorado Boulder

    June 8, 2016

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    LANDSAT 7

    The perpetually ice-covered lakes in Antarctica’s McMurdo Dry Valleys preserve the dissolved remnants of black carbon from thousand-year-old wildfires as well as modern day fossil fuel use, according to a new study led by the University of Colorado Boulder.

    The distinctive molecular signatures can provide researchers with a glimpse into the planet’s long history of combustion. Atmospheric black carbon, which is generated by wildfires or fossil fuel use, becomes preserved in glaciers, which in turn serve as long-term reservoirs and chemical time capsules.

    The McMurdo Dry Valleys of Antarctica are the largest ice-free region of the continent and are considered a polar desert environment due to their low humidity, scarce precipitation and lack of plant life. During the summer, glacial melt feeds closed-basin lakes. Some of these lakes have saline bottom waters from drawdown events about a thousand years ago.

    These briny bottom waters preserve the chemical signatures of fires that occurred thousands of years ago and thousands of miles away, the study found. Dissolved black carbon is present in the world’s oceans as well as on land, and now has been found to be detectible in the pristine, isolated lakes of Antarctica.

    “We know the long-term history of these lakes and that there are no local forest fires burning nearby, so we can be more certain that these woody signatures have come over from South America, Africa or Australia, for instance,” said Alia Khan, a graduate researcher in the Institute of Arctic and Alpine Research (INSTAAR) at CU-Boulder and lead author of the study.

    “Overall there have been relatively few direct measurements of dissolved black carbon in the cryosphere due to the difficulty of sample collection from these remote environments,” Khan added. “These are the first we know of from freshwater lakes in Antarctica.”

    Closer to the top of the lakes, the researchers also found low, but distinct, concentrations of man-made black carbon, possibly from helicopter use in and around the Antarctic continent.

    The study may open new avenues of inquiry into how black carbon signatures have shifted over time and how dissolved black carbon is transported to the world’s oceans and lakes.

    “Having a new chemical tool that allows us to identify the source and transformation of black carbon is very exciting,” said Diane McKnight, a professor of Civil, Environmental and Architectural Engineering at CU-Boulder, an INSTAAR fellow and a co-author of the study.

    See the full article here .

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    U Colorado Campus

    As the flagship university of the state of Colorado, CU-Boulder is a dynamic community of scholars and learners situated on one of the most spectacular college campuses in the country. As one of 34 U.S. public institutions belonging to the prestigious Association of American Universities (AAU) – and the only member in the Rocky Mountain region – we have a proud tradition of academic excellence, with five Nobel laureates and more than 50 members of prestigious academic academies.

    CU-Boulder has blossomed in size and quality since we opened our doors in 1877 – attracting superb faculty, staff, and students and building strong programs in the sciences, engineering, business, law, arts, humanities, education, music, and many other disciplines.

    Today, with our sights set on becoming the standard for the great comprehensive public research universities of the new century, we strive to serve the people of Colorado and to engage with the world through excellence in our teaching, research, creative work, and service.

     
  • richardmitnick 10:33 am on June 9, 2016 Permalink | Reply
    Tags: , Geology, How two tiny dots defy the history of life and the solar system,   

    From New Scientist: “How two tiny dots defy the history of life and the solar system” 

    NewScientist

    New Scientist

    20 April 2016 [In social media today]
    Colin Stuart

    Two specks of rock that formed when Earth was young suggest we’ve got to rethink everything from the story of the solar system to the origins of life.

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    Neil Stevens

    OF THE 200,000 shards of rock that Mark Harrison has retrieved from Australia since the mid-1980s, only one contained what he was looking for. Two flecks of graphite, each barely the size of a red blood cell. Small, perhaps, but capable of overturning everything we know about life on Earth. Harrison, a geologist at the University of California, Los Angeles, remembers thinking to himself: “By golly, they’re a dead ringer for a biogenic origin.” Biogenic means made by life – but how? These graphite flecks were found in a zircon crystal that had lain trapped deep in the Jack Hills of Western Australia for 4.1 billion years. So they seem to imply our planet was inhabited at least 300 million years earlier than anyone had previously imagined.

    What’s more, these first living organisms would date from a time before our planet was thought capable of harbouring any life at all. In these early years, Earth was supposedly a molten hellhole racked by volcanism and bombarded by space debris, zinging around a solar system yet to find inner peace. If Harrison’s fossils are all they seem, they wouldn’t only rewrite the history of life and Earth – but the entire solar system’s as well.

    When it came to explaining how these things all got started, we thought we had it more or less worked out. Some 4.6 billion years ago, a vast cloud of dust and gas in some corner of an unremarkable galaxy began to collapse into a dense ball of matter. As more and more surrounding material was pulled towards it, the temperature and pressure at its core increased, to the point where nuclear fusion kicked in. This released vast quantities of energy and marked the moment our sun became a star.
    ..

    As the newborn star slowly began to spin, smaller bodies started to coalesce in orbit around it. Close in, vast quantities of water ice were boiled away, leaving only metallic compounds behind to form the smaller rocky planets. Further out, cooler temperatures allowed giant worlds of ice and gas to form. All in a single plane along smooth, near-circular tracks.

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    Rewriters of the solar system: tiny shards of zircon. Elizabeth Bell, et al./UCLA

    It was a nice story, but as further details emerged, it became apparent that this picture was incomplete. For one thing, it struggled to explain the quantity and distribution of the so-called Trojan asteroids, thousands of tiny bodies that chase after Jupiter in its orbit. The Kuiper belt, the icy band beyond Neptune that Pluto belongs to, was equally difficult to justify: many of its bodies orbit at far greater angles to the planetary plane than the conventional picture would allow. Perhaps most perplexing of all, however, was the evidence our cosmic neighbourhood had once been under heavy bombardment. Rocks returned to Earth by the Apollo astronauts suggested the widespread cratering on our own moon was the result of a protracted assault which took place 3.9 billion years ago – a ruction the conventional model found hard to explain.

    The solution, named after the city in France where it was devised in 2005, was the Nice model. In this refinement of the traditional story, our solar system’s four giant planets started out much closer together than they are today. This configuration was unstable, leading to hundreds of millions of years of gravitational tussling, during which the giant planets migrated into their current positions, disturbing the millions of tiny bodies littering the ancient solar system. Many fell under Jupiter’s gravitational influence, becoming its Trojan followers, while others settled in the solar system’s outer regions as highly angled denizens of the Kuiper belt.

    Meanwhile, asteroids in the band between Mars and Jupiter were dislodged from orbit, many going on to collide with the innermost planets. This period of intense activity, known as the Late Heavy Bombardment (LHB), would have left deep craters on the moon and given our fledgling planet a serious knock during the turbulent early stages of its development.

    The small number of surviving solid rocks from this period have led us to picture early Earth as a fiery world covered in volcanoes bursting through a molten crust. The LHB’s few hundred million years of constant collisions contributed to a nightmarish landscape so extreme that the geological period is known as the Hadean, after the Greek god of the underworld. The existence of life in such a hellscape was considered preposterous. Instead, the first traces of biogenic carbon, dated at 3.8 billion years old, neatly coincide with the time Earth was finally at peace and the bombardment from outer space had slowed.

    Hence the excitement if Harrison’s fleck of graphite really is what it appears to be: evidence not only of our planet’s oldest known life form, but one that emerged at an impossible time. His smoking gun was the ratio of isotopes carbon-13 and carbon-12, within the sample. “If you were looking at this carbon ratio today, you would say it was biogenic,” he says.

    Astonishing as it is, Chris Ballentine from the University of Oxford cautions against getting carried away. “It is one inclusion in one zircon,” he says. “But this sets the bar for people to find more and really show there was life around back then.”

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    Hellmouth: Australia’s Jack Hills hark back to Earth’s violent youth. Birger Rasmussen/Curtin University

    Life or no life, it’s just the latest piece of evidence from the Jack Hills suggesting Earth’s hellish youth was more short-lived than astronomers thought possible. As far back as 1999, geologists uncovered other zircons in this astonishing terrain that indicated part of Earth’s surface had cooled and solidified 4.4 billion years ago. What’s more, measurements of how much oxygen the rocks contained suggested that Earth had been mild enough to support liquid water.

    Further evidence that not all was right in the established picture of Earth and the solar system came in 2013, when Judith Coggon, then at the University of Bonn, Germany, was analysing another contender for the planet’s oldest rock – on the other side of the world in Greenland. There she found evidence that Earth contained significant quantities of gold and platinum as far back as 4.1 billion years ago – even though these metals were thought to have been delivered only later by the Late Heavy Bombardment.

    Yet more contention came last year, when Nathan Kaib from the University of Oklahoma, along with John Chambers from the Carnegie Institution in Washington DC, published the results of their latest simulations of solar system formation. What they found seemed to sound the death knell for the Nice model. In 85 per cent of cases, the inner solar system ended up with fewer than the four rocky worlds it has today. “More often than not you lose Mercury,” says Kaib. Only 1 per cent of the time could they create a solar system that looked like the one we recognise. It would not be the first time the Nice model has been modified to take account of problems (see “Mystery of the missing planet“), but this was a problem of a different magnitude. “It seems very unlikely that you can get the outer solar system architecture and protect the inner planets,” he says.

    Kaib has a surprisingly simple solution. The giant planets still migrated, producing the Jovian Trojans and the Kuiper belt, but they did so much earlier – while the innermost planets were still forming. By turning up to the party fashionably late, Earth dodged a bullet. The early migration of the giant planets would have scattered most of the larger impactors by the time Earth’s formation was complete. That works well, says Zoë Leinhardt, from the University of Bristol, UK. “The latter part of Earth’s formation would have been calmer, as opposed to having formed and then being smacked upside the head.”

    4

    It’s an appealing theory, explaining not only why the solar system looks the way it does, but how Earth became friendly to life so early. But one final mystery remains. If the giant planet migration happened before Earth and the moon had formed, then something else must have been responsible for the craters on the lunar surface. But what?

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    Up for grabs: the origins of the moon’s impact craters. NASA

    David Minton from Purdue University thinks the answer lies closer to home. “In the Nice model, most of the LHB impactors come from the asteroid belt,” he says. “But the distribution of crater sizes on the moon and the distribution of asteroids don’t match.” Matija Cuk of the SETI Institute agrees. “If the LHB really was just asteroids being thrown at the moon en masse, there should be a lot more big lunar basins, and there aren’t,” he says. Minton believes he might have found an alternative source for the LHB: Mars.

    He’s still working on the finer details, but he presented the concept to the American Astronomical Society’s Division on Dynamical Astronomy at their meeting in May 2015. One fact working in its favour is that the Red Planet’s northern hemisphere is low-lying and considerably flatter than the highlands in the south. “Many have suggested that’s because the northern area is a giant basin formed by a 2000-kilometre impactor,” says Minton. Debris thrown up by the formation of this so-called Borealis basin could have bombarded the moon, and Earth, 3.9 billion years ago.

    Cuk has an even more radical explanation. “To me it is not clear at all that there was a spike in lunar bombardment 3.9 billion years ago,” he says. The Apollo samples that led to the assumption were returned from several different sites on the moon, with many showing evidence of impacts clustered around that time. But Cuk believes the Apollo samples all came from the impact or impacts that formed the Imbrium basin – one of the large, dark patches that makes up the “Man in the Moon”. Rocky shrapnel from this event could have contaminated disparate parts of the lunar surface, meaning that what at first looked like a host of simultaneous impacts might have only been a handful. “The idea of the carpet-bombing of the moon 3.9 billion years ago has gone away,” he says. If you could prove the impacts that caused the cratering on the moon were less of a spike and more of a steady drip, then the Nice model could be saved after all. Just as crucially, it would have profound implications for conditions on our infant planet. “If the impacts were more smeared out, early Earth wouldn’t have been total hell,” says Cuk.

    Either way, with relative calmness kicking in sooner in Earth’s history, life could have emerged more quickly to leave its mark in the Jack Hills zircon. “Pushing giant planet migration back earlier would be consistent with what we found,” says Harrison. Future work will look at cementing this idea. Harrison has already identified another graphite inclusion in a separate Jack Hills zircon and will be analysing the ratio of its carbon isotopes within the next few months.

    If Harrison’s hunch is right, then the life forms we had previously thought of as our earliest ancestors, dating from 3.8 billion years ago, weren’t the beginning of the evolutionary tree at all. Instead life on Earth began hundreds of millions of years earlier, almost as soon as the planet was ready for it. Such a scenario would raise hopes for the speed and ease with which biology can take hold, and of its aptitude for sticking around in an unfriendly cosmos. According to Harrison, “it makes the notion of life elsewhere in the universe that much more likely.” Our revised history could point to a more interesting future.

    ______________________________________________________________________________

    Mystery of the missing planet

    Ever sensed something was missing? Researchers modelling our solar system have. Their best stab at explaining how our cosmic neighbourhood came to be suggests there shouldn’t be four giant planets in the outer solar system – there should be five.

    In 2011, simulations suggested that without this mysterious fifth planet, intense gravitational interactions in the early solar system would have had disastrous consequences. As the four giants slowly creaked into their current positions, they would have disrupted their smaller neighbours, making the modern solar system all but impossible.

    But with five giant planets jostling for supremacy, the migration would have taken place quickly enough to leave the innermost rocky planets virtually unharmed. What’s more, one of the quintet would have been slingshotted into the furthest reaches of the solar system, leaving us with the four outermost planets as we see them today.

    Where exactly did this guardian angel end up? Speculation surrounding the existence of “Planet Nine” has long bubbled under the surface, but earlier this year the excitement finally burst when two astronomers from the California Institute of Technology announced they might have found it. With an orbital radius 600 times greater than Earth’s, this candidate Planet Nine would take at least 10,000 years to complete a single lap of the sun, making it one of our solar system’s most distant objects. Its existence has been inferred from the unusual clustering of half a dozen small objects beyond Pluto, which would be difficult to explain without a distant planet’s gravitational pull. The logic holds up, but direct observation has eluded us thus far.

    It would be a remarkable find. Its discovery, while a pain for textbook publishers and quiz show contestants, would support the five-giant scenario for the solar system’s formation. “If Planet Nine exists, that’s where it must have come from,” says Matija Cuk of the SETI Institute in California.

    ______________________________________________________________________________

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  • richardmitnick 5:23 pm on May 12, 2016 Permalink | Reply
    Tags: , , Found: surviving evidence of Earth’s formative years, Geology   

    From Carnegie: “Found: surviving evidence of Earth’s formative years” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    May 12, 2016
    Scientific Area:
    Earth & Planetary Science
    Reference to Person:
    Richard Carlson

    1
    Photographs from Baffin Island fieldwork, courtesy of Don Francis of McGill University.

    New work from a team including Carnegie’s Hanika Rizo and Richard Carlson, as well as Richard Walker from the University of Maryland, has found material in rock formations that dates back to shortly after Earth formed. The discovery will help scientists understand the processes that shaped our planet’s formative period and its internal dynamics over the last 4.5 billion years. It is published* by Science.

    Earth formed from the accretion of matter surrounding the young Sun. The heat of its formation caused extensive melting of the planet, leading Earth to separate into two layers when the denser iron metal sank inward toward the center, creating the core and leaving the silicate-rich mantle floating above.

    Over the subsequent 4.5 billion years of Earth’s evolution, convection in Earth’s interior, like water boiling on a stove, caused deep portions of the mantle to rise upwards, melt, and then separate once again by density. The melts, since they were less dense than the unmelted rock, rose to form Earth’s crust, while the denser residues of the melting sank back downward, altering the mantle’s chemical composition in the process.

    The mantle residues of crust formation were previously believed to have mixed back into the mantle so thoroughly that evidence of the planet’s oldest geochemical events, such as core formation, was lost completely.

    However, the research team—which also included Sujoy Mukhopadhyay and Vicky Manthos of University of California Davis, Don Francis of McGill University, and Matthew Jackson, a Carnegie alumnus now at University of California Santa Barbara—was able find a geochemical signature of material left over from the early melting events that accompanied Earth’s formation. They found it in relatively young rocks both from Baffin Island, off the coast of northern Canada, and from the Ontong-Java Plateau in the Pacific Ocean, north of the Solomon Islands.

    These rock formations are called flood basalts because they were created by massive eruptions of lava. The solidified lava itself is only between 60 and 120 million years old, depending on its location. But the team discovered that the molten material from inside the Earth that long ago erupted to create these plains of basaltic rock owes its chemical composition to events that occurred over 4.5 billion years in the past.

    Here’s how they figured it out:

    They measured variations in these rocks of the abundance of an isotope of tungsten—the same element used to make filaments of incandescent light bulbs. Isotopes are versions of an element in which the number of neutrons in each atom differs from the number of protons. (Each element contains a unique number of protons.) These differing neutron numbers mean that each isotope has a slightly different mass.

    Why tungsten? Tungsten contains one isotope of mass 182 that is created when an isotope of the element hafnium undergoes radioactive decay, meaning its elemental composition changes as it gives off radiation. The time it takes for half of any quantity of hafnium-182 to decay into tungsten-182 is 9 million years. This may sound like a very long time, but is quite rapid when it comes to planetary formation timescales. Rocky planets like Earth or Mars took about 100 million years to form.

    The team determined that the basalts from Baffin Island, formed by a 60-million-year-old eruption from the mantle hot-spot currently located beneath Iceland, and the Ontong-Java Plateau, which was formed by an enormous volcanic event about 120 million years ago, contain slightly more tungsten-182 than other young volcanic rocks.

    Because all the hafnium-182 decayed to tungsten-182 during the first 50 million years of Solar System history, these findings indicate that the mantle material that melted to form the flood basalt rocks that the team studied originally had more hafnium than the rest of the mantle. The likely explanation for this is that the portion of Earth’s mantle from which the lava came had experienced a different history of iron separation than other portions of the mantle (since tungsten is normally removed to the core along with the iron.)

    It was a surprise to the team that such material still exists in Earth’s interior.

    “This demonstrates that some remnants of the early Earth’s interior, the composition of which was determined by the planet’s formation processes, still exist today,” explained lead author Rizo, now at Université du Québec à Montréal.

    “The survival of this material would not be expected given the degree to which plate tectonics has mixed and homogenized the planet’s interior over the past 4.5 billion years, so these findings are a wonderful surprise,” added Carlson, Director of Carnegie’s Department of Terrestrial Magnetism.

    The team’s discovery offers new insight into the chemistry and dynamics that shaped our planet’s formative processes. Going forward, scientists will have to hunt for other areas showing outsized amounts of tungsten-182 with the hope of illuminating both the earliest portion of Earth’s history as well as the place in Earth’s interior where this ancient material is stored.

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    No descriptive captions present

    *Science paper:
    Preservation of Earth-forming events in the tungsten isotopic composition of modern flood basalts

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    Carnegie Institution of Washington Bldg

    Andrew Carnegie established a unique organization dedicated to scientific discovery “to encourage, in the broadest and most liberal manner, investigation, research, and discovery and the application of knowledge to the improvement of mankind…” The philosophy was and is to devote the institution’s resources to “exceptional” individuals so that they can explore the most intriguing scientific questions in an atmosphere of complete freedom. Carnegie and his trustees realized that flexibility and freedom were essential to the institution’s success and that tradition is the foundation of the institution today as it supports research in the Earth, space, and life sciences.

     
  • richardmitnick 7:31 am on April 21, 2016 Permalink | Reply
    Tags: , , Geology   

    From ANU: “Stories in the stone: Geology students venture into the field” 

    ANU Australian National University Bloc

    Australian National University

    1

    If rocks could speak, they would have a lot to say. Even without a voice, they’re great story-tellers. So long as you know how to listen.

    “I didn’t really get interested in geology until the later years of high school, when I realised that you can tell a story from rocks,” says Eleni Ravanis, an ANU student who has just completed a nine-day geology field trip at Wee Jasper in NSW.

    2

    As part of the field trip students are learning how to map the type and structure of rocks to understand what has happened in past environments.

    In a limestone structure, students see a story that begins under the sea. In a fold or a fault, they understand the shifting of the Earth’s tectonic plates.

    “It’s pretty cool to infer that just from looking at a rock,” says Eleni.

    2

    3

    The field trip was also the ultimate Aussie experience for Dutch exchange student, Jesse Zondervan.

    “We’re staying in Wee Jasper at a homestead in the bush with little sheep running around,” he says.

    Each morning the students leave the property and four-wheel drive across steep terrain to the upper reaches of Lake Burrinjuck. They drive past impressive folds and ripples in the Earth before arriving at a geological formation called the “Shark’s Mouth”.

    4

    The students learn a range of techniques in mapping and structural geology and they admit the course can be demanding.

    “It’s a steep learning curve but I’ve definitely improved my skills in the field,” says Jack Dennison, a former Sydney-sider who moved to Canberra for the well-regarded Earth sciences program.

    5

    But the best part about the course is the chance to interact with other students and make new friends.

    “It’s been a very intense few days but we’re all in it together,” says Eleni.

    “I’ve made better friends with people I didn’t really know before this course. We all help each other out.”

    And as the students retreat to their homestead to share the stories of the rocks, they have the chance to share some of their own.

    6

    f you would like to hone your geology skills you might like to try the Introduction to Structural and Field Geology course.

    See the full article here .

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    ANU Campus

    ANU is a world-leading university in Australia’s capital city, Canberra. Our location points to our unique history, ties to the Australian Government and special standing as a resource for the Australian people.

    Our focus on research as an asset, and an approach to education, ensures our graduates are in demand the world-over for their abilities to understand, and apply vision and creativity to addressing complex contemporary challenges.

     
  • richardmitnick 5:34 pm on April 6, 2016 Permalink | Reply
    Tags: , , Geology, ,   

    From phys.org: “Supernovae showered Earth with radioactive debris” 

    physdotorg
    phys.org

    April 6, 2016
    No writer credit found

    1
    Artist’s impression of supernova. Credit: Greg Stewart, SLAC National Accelerator Lab

    An international team of scientists has found evidence of a series of massive supernova explosions near our solar system, which showered the Earth with radioactive debris.

    The scientists found radioactive iron-60 in sediment and crust samples taken from the Pacific, Atlantic and Indian Oceans.

    The iron-60 was concentrated in a period between 3.2 and 1.7 million years ago, which is relatively recent in astronomical terms, said research leader Dr Anton Wallner from The Australian National University (ANU).

    “We were very surprised that there was debris clearly spread across 1.5 million years,” said Dr Wallner, a nuclear physicist in the ANU Research School of Physics and Engineering. “It suggests there were a series of supernovae, one after another.

    “It’s an interesting coincidence that they correspond with when the Earth cooled and moved from the Pliocene into the Pleistocene period.”

    The team from Australia, the University of Vienna in Austria, Hebrew University in Israel, Shimizu Corporation and University of Tokyo, Nihon University and University of Tsukuba in Japan, Senckenberg Collections of Natural History Dresden and Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, also found evidence of iron-60 from an older supernova around eight million years ago, coinciding with global faunal changes in the late Miocene.

    Some theories suggest cosmic rays from the supernovae could have increased cloud cover.

    Cassiopeia A false color image using Hubble and Spitzer telescopes and Chandra X-ray Observatory. Credit NASA JPL-Caltech
    Cassiopeia A false color image using Hubble and Spitzer telescopes and Chandra X-ray Observatory. Credit NASA JPL-Caltech

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    The scientists believe the supernovae in this case were less than 300 light years away, close enough to be visible during the day and comparable to the brightness of the Moon.

    Although Earth would have been exposed to an increased cosmic ray bombardment, the radiation would have been too weak to cause direct biological damage or trigger mass extinctions.

    The supernova explosions create many heavy elements and radioactive isotopes which are strewn into the cosmic neighbourhood.

    One of these isotopes is iron-60 which decays with a half-life of 2.6 million years, unlike its stable cousin iron-56. Any iron-60 dating from the Earth’s formation more than four billion years ago has long since disappeared.

    The iron-60 atoms reached Earth in minuscule quantities and so the team needed extremely sensitive techniques to identify the interstellar iron atoms.

    “Iron-60 from space is a million-billion times less abundant than the iron that exists naturally on Earth,” said Dr Wallner.

    Dr Wallner was intrigued by first hints of iron-60 in samples from the Pacific Ocean floor, found a decade ago by a group at TU Munich.

    He assembled an international team to search for interstellar dust from 120 ocean-floor samples spanning the past 11 million years.

    The first step was to extract all the iron from the ocean cores. This time-consuming task was performed by two groups, at HZDR and the University of Tokyo.

    The team then separated the tiny traces of interstellar iron-60 from the other terrestrial isotopes using the Heavy-Ion Accelerator at ANU and found it occurred all over the globe.

    The age of the cores was determined from the decay of other radioactive isotopes, beryllium-10 and aluminium-26, using accelerator mass spectrometry (AMS) facilities at DREsden AMS (DREAMS) of HZDR, Micro Analysis Laboratory (MALT) at the University of Tokyo and the Vienna Environmental Research Accelerator (VERA) at the University of Vienna.

    The dating showed the fallout had only occurred in two time periods, 3.2 to 1.7 million years ago and eight million years ago. Current results from TU Munich are in line with these findings.

    A possible source of the supernovae is an ageing star cluster, which has since moved away from Earth, independent work led by TU Berlin has proposed in a parallel publication. The cluster has no large stars left, suggesting they have already exploded as supernovae, throwing out waves of debris.

    More information: Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe, Nature, DOI: 10.1038/nature17196

    The science team:

    A. Wallner, J. Feige, N. Kinoshita, M. Paul, L. K. Fifield, R. Golser, M. Honda, U. Linnemann, H. Matsuzaki, S. Merchel, G. Rugel, S. G. Tims, P. Steier, T. Yamagata & S. R. Winkler

    Affiliations

    Department of Nuclear Physics, Research School of Physics and Engineering, The Australian National University (ANU), Canberra, Australian Capital Territory 2601, Australia
    A. Wallner, L. K. Fifield & S. G. Tims
    University of Vienna, Faculty of Physics—Isotope Research, VERA Laboratory, Währinger Straße 17, 1090 Vienna, Austria
    J. Feige, R. Golser, P. Steier & S. R. Winkler
    Institute of Technology, Shimizu Corporation, Tokyo 135-8530, Japan
    N. Kinoshita
    Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
    M. Paul
    Graduate School of Pure and Applied Sciences, University of Tsukuba, Ibaraki 305-8577, Japan
    M. Honda
    Senckenberg Collections of Natural History Dresden, GeoPlasmaLab, Königsbrücker Landstraße 159, Dresden 01109, Germany
    U. Linnemann
    MALT (Micro Analysis Laboratory, Tandem accelerator), The University Museum, The University of Tokyo, Tokyo 113-0032, Japan
    H. Matsuzaki
    Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Helmholtz Institute for Resource Technology, 01328 Dresden, Germany
    S. Merchel & G. Rugel
    Graduate School of Integrated Basic Sciences, Nihon University, Tokyo 156-8550, Japan
    T. Yamagata

    Contributions

    A.W. initiated the study and wrote the main paper together with J.F., M.P. and L.K.F.; all authors were involved in the project and commented on the paper. A.W., with J.F., L.K.F. and S.R.W., organized the Eltanin sediment samples. N.K. and M.P. organized the crust samples. S.M. and U.L. organized the nodules. J.F. and S.M. were primarily responsible for sample preparation of the sediment and nodules and N.K. was responsible for the crusts. A.W., L.K.F. and S.G.T. performed the AMS measurements for 60Fe at the ANU. P.S., S.R.W., J.F. and A.W. performed the 26Al and 10Be measurements at VERA. G.R., S.M. and J.F. performed 10Be measurements at HZDR. N.K., M.H., H.M. and T.Y. performed 10Be measurements at MALT. J.F., A.W. and N.K. performed the data analysis.

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 11:35 am on April 6, 2016 Permalink | Reply
    Tags: , , Geology, Rock falls   

    From Eos: “A Warm Day Can Trigger Rockfalls” 

    Eos news bloc

    Eos

    5 April 2016
    Lucas Joel

    Research on a cliff face in Yosemite National Park finds that when rockfalls happen without an obvious cause, ordinary warming in the Sun could be the culprit.

    1
    Researchers Brian Collins and Greg Stock download data that indicate how much partially detached granitic slabs on a mountain face have moved as a result of daily temperature variations. Such movement is a precursor to a rockfall. Credit: Valerie Zimmer, National Park Service

    Geologists have long known that earthquakes, along with precipitation and freeze-thaw cycles, can trigger giant slabs of rock to fall from mountain faces, to thunderous effect. Now a research team, following a clue from rock climbers at Yosemite National Park, has shed some light on why rockfalls will sometimes happen in the middle of a clear, sunny day without an obvious cause.

    The reason: Daily, seasonal, and annual temperature fluctuations can cause the granite slabs to slowly peel away, or exfoliate, then suddenly fracture and fall, the scientists reported last week in Nature Geoscience.

    “There’s this hypothesis that thermal stresses could cause rocks to fracture and break and fall. That isn’t anything new—people have been thinking about that for over a hundred years. But it hadn’t been measured,” said Brian Collins, a research civil engineer with the U.S. Geological Survey in Menlo Park, Calif., and a coauthor of the paper.

    Climbers Point the Way

    He and coauthor Greg Stock, who is Yosemite’s first-ever park geologist, had heard stories from Yosemite’s many rock climbers about their climbing gear getting stuck in the cracks of detached granite slabs—or “flakes” as Collins and Stock say—as hot days wore on into cool nights. This gave the duo the idea to climb to a flake and install “crackmeters”—instruments the researchers devised themselves that measure minute changes in crack width over time.

    “This isn’t just [one person who] put the gear in wrong and couldn’t get it back out; lots of people are going through this,” Collins said. “We thought, maybe it’s that the rock flakes are moving back into the cliff, and if that’s the case, maybe it’s measurable.”

    They specifically put the crackmeters in a gap behind a granite flake about 19 meters long, 4 meters wide, and about 15 meters above the park’s valley floor. After 1 month, the crackmeter data indicated the flake, from night to day, was moving “in and out of the wall by up to a centimeter each day,” said Collins. “That was a big huge ‘Wow!’—we had no idea it was going to move that much.”

    Thermal Weathering

    Ultimately, Collins and Stock monitored the crack for 3.5 years. Over that time, they found that crack widths vary seasonally, with the hot summer months producing the widest offsets. They also found that the rock’s outward expansion was cumulative: the flake would move forward more and more each year, building on the previous season’s progress.

    2
    An exfoliation-type rockfall cascades from Yosemite Valley’s El Capitan on a clear day in October 2010. Credit: Tom Evans

    Millions of people visit Yosemite every year, so the park’s staff has kept thorough records of rockfalls there. These records indicate that spontaneous rockfalls—the kind that happen for no obvious reason—occur most often during the hot summer months. “We discovered that these flakes actually deform quite a bit, much more than we had originally thought, and we’ve been able to link that to how the process of thermal heating can move a flake in and out,” Collins said. Such movement will “eventually lead to fracture,” he added.

    Still, because fracture propagation is nonlinear, it is not possible to predict how far off in the future a flake might pass its threshold and detach, Collins explained.

    “These results are scientifically wonderful, and they have implications for landscape evolution and rockfall hazards in other high mountain areas,” commented landslide expert David Petley of the University of East Anglia in the United Kingdom in a 30 March blog post about the new study.

    “Whilst higher than expected levels of rockfalls have been observed in the summer months in many mountain landscapes, in general I think it has been assumed that this is mostly associated with the melting of ice in cracks. Whilst this ice driven process is undoubtedly still important, Collins and Stock (2016) has given us cause to think about other processes too,” added Petley, whose editorially independent The Landslide Blog is hosted by the American Geophysical Union, publisher of Eos.org.

    In future work, Collins explains, it may be possible to determine “how many [thermal] cycles it takes to eventually fracture the rock,” which might help Yosemite’s staff identify slabs that may be close to collapsing and thus endangering park visitors.

    Rockfall triggering by cyclic thermal stressing of exfoliation fractures

    Science team:
    Brian D. Collins, Greg M. Stock

    Affiliations

    US Geological Survey, Landslide Hazards Program, 345 Middlefield Road, MS-973, Menlo Park, California 94025, USA
    Brian D. Collins
    National Park Service, Yosemite National Park, El Portal, California 95318, USA
    Greg M. Stock

    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 10:02 pm on April 5, 2016 Permalink | Reply
    Tags: , , Geology   

    From Eos: “Massive Ancient Tectonic Slab Found Below the Indian Ocean” 

    Eos news bloc

    Eos

    1 April 2016
    Cody Sullivan

    Scientists discover a surprisingly positioned tectonic plate, buried below the southern Indian Ocean, that spans the entire mantle.

    1
    Seismic wave velocity structure in the deep Earth revealed through seismic tomography. Earthquakes generate seismic energy near their epicenters (yellow markers), and the energy is recorded at seismic stations around the world (red markers). Seismic waves (depicted as yellow rays emanating from an earthquake beneath Spain) are disrupted as they travel through fast (blue) and slow (red) structures in the Earth. By mapping these anomalous structures on a global scale, researchers have uncovered a previously unidentified tectonic plate that sank into Earth’s mantle more than 130 million years ago beneath the southern Indian Ocean. Credit: Nathan Simmons, using MATLAB.

    A team of researchers recently discovered an ancient relic hidden within Earth: a tectonic plate resting beneath the southern Indian Ocean. Scientists have found other tectonic plates that sank below Eurasia and North America, but here Simmons et al. describe the unique structure of this newly discovered slab, which they named the Southeast Indian Slab (SEIS). The slab has at least one feature scientists have rarely seen before: It maintains its slab-like structure all the way from the upper mantle near Earth’s crust down to the region where the mantle meets the planet’s superheated core. The Farallon plate beneath North America is a well-known example of this—but it was expected to exist and sank much more recently than the SEIS. In addition, not only does the SEIS traverse the entire mantle, but it also becomes more vertical along one end, so much so that it stands almost vertically between the crust and core along the eastern edge, whereas the western portion is more horizontal.

    Researchers can make out structures beneath Earth’s crust by examining the speed at which seismic waves generated by earthquakes and similar Earth-shattering events—known as P and S waves—travel through Earth. Here the researchers used wave data from 12,607 seismic events dating back to the 1960s, collected by 7783 seismic stations around the world, to develop the model that identified the ancient slab.

    Once this tectonic slab was identified, the team looked at the region’s tectonic history over millions of years to determine where and when this plate was on the surface. They determined that the slab was once along the eastern portion of the early supercontinent of Gondwana. Then, sometime during the Triassic or Jurassic period, which stretched from 250 million years ago to 145 million years ago, the slab plunged underneath another plate. They further concluded that the subduction, or the sinking of the Southeast Indian Slab beneath another plate, terminated around 130 to 140 million years ago in the Mesozoic era, around the same time that the tectonic plates under eastern Gondwana began to separate and split up the continent.

    Tectonic plates usually sink down into the mantle at a rate of about 1 centimeter per year or more; they don’t necessarily melt but instead bunch up at the base of the mantle and eventually assimilate or become undetectable as their temperature increases. However, if the researchers accurately estimated the timing of their newly discovered slab’s subduction, this slab must have stalled in a transition zone before descending deeper down into the mantle, allowing the slab to persist in the mantle longer than any other known plate. (Geophysical Research Letters, doi:10.1002/2015GL066237, 2015)

    Citation: Sullivan, C. (2016), Massive ancient tectonic slab found below the Indian Ocean, Eos, 97, doi:10.1029/2016EO049219. Published on 1 April 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.

     
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