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  • richardmitnick 5:36 pm on January 10, 2018 Permalink | Reply
    Tags: , , , , , , , Meteorites, , Organic chemistry, STXM-scanning transmission X-ray microscope, We’re looking at the organic ingredients that can lead to the origin of life” including the amino acids needed to form proteins,   

    From LBNL: “Ingredients for Life Revealed in Meteorites That Fell to Earth” 

    Berkeley Logo

    Berkeley Lab

    January 10, 2018
    Glenn Roberts Jr.
    geroberts@lbl.gov
    (510) 486-5582

    1
    A blue crystal recovered from a meteorite that fell near Morocco in 1998. The scale bar represents 200 microns (millionths of a meter). (Credit: Queenie Chan/The Open University, U.K.)

    Two wayward space rocks, which separately crashed to Earth in 1998 after circulating in our solar system’s asteroid belt for billions of years, share something else in common: the ingredients for life. They are the first meteorites found to contain both liquid water and a mix of complex organic compounds such as hydrocarbons and amino acids.

    A detailed study of the chemical makeup within tiny blue and purple salt crystals sampled from these meteorites, which included results from X-ray experiments at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), also found evidence for the pair’s past intermingling and likely parents. These include Ceres, a brown dwarf planet that is the largest object in the asteroid belt, and the asteroid Hebe, a major source of meteorites that fall on Earth.

    The study, published Jan. 10 in the journal Science Advances, provides the first comprehensive chemical exploration of organic matter and liquid water in salt crystals found in Earth-impacting meteorites. The study treads new ground in the narrative of our solar system’s early history and asteroid geology while surfacing exciting possibilities for the existence of life elsewhere in Earth’s neighborhood.

    “It’s like a fly in amber,” said David Kilcoyne, a scientist at Berkeley Lab’s Advanced Light Source (ALS), which provided X-rays that were used to scan the samples’ organic chemical components, including carbon, oxygen, and nitrogen.

    LBNL/ALS

    Kilcoyne was part of the international research team that prepared the study.

    While the rich deposits of organic remnants recovered from the meteorites don’t provide any proof of life outside of Earth, Kilcoyne said the meteorites’ encapsulation of rich chemistry is analogous to the preservation of prehistoric insects in solidified sap droplets.

    Queenie Chan, a planetary scientist and postdoctoral research associate at The Open University in the U.K. who was the study’s lead author, said, “This is really the first time we have found abundant organic matter also associated with liquid water that is really crucial to the origin of life and the origin of complex organic compounds in space.”

    She added, “We’re looking at the organic ingredients that can lead to the origin of life,” including the amino acids needed to form proteins.

    If life did exist in some form in the early solar system, the study notes that these salt crystal-containing meteorites raise the “possibility of trapping life and/or biomolecules” within their salt crystals. The crystals carried microscopic traces of water that is believed to date back to the infancy of our solar system – about 4.5 billion years ago.

    Chan said the similarity of the crystals found in the meteorites – one of which smashed into the ground near a children’s basketball game in Texas in March 1998 and the other which hit near Morocco in August 1998 – suggest that their asteroid hosts may have crossed paths and mixed materials.

    There are also structural clues of an impact – perhaps by a small asteroid fragment impacting a larger asteroid, Chan said.

    This opens up many possibilities for how organic matter may be passed from one host to another in space, and scientists may need to rethink the processes that led to the complex suite of organic compounds on these meteorites.

    “Things are not as simple as we thought they were,” Chan said.

    There are also clues, based on the organic chemistry and space observations, that the crystals may have originally been seeded by ice- or water-spewing volcanic activity on Ceres, she said.

    “Everything leads to the conclusion that the origin of life is really possible elsewhere,” Chan said. “There is a great range of organic compounds within these meteorites, including a very primitive type of organics that likely represent the early solar system’s organic composition.”

    Chan said the two meteorites that yielded the 2-millimeter-sized salt crystals were carefully preserved at NASA’s Johnson Space Center in Texas, and the tiny crystals containing organic solids and water traces measure just a fraction of the width of a human hair. Chan meticulously collected these crystals in a dust-controlled room, splitting off tiny sample fragments with metal instruments resembling dental picks.

    2
    These ALS X-ray images show organic matter (magenta, bottom) sampled from a meteorite, and carbon (top). (Credit: Berkeley Lab)

    “What makes our analysis so special is that we combined a lot of different state-of-the-art techniques to comprehensively study the organic components of these tiny salt crystals,” Chan said.

    Yoko Kebukawa, an associate professor of engineering at Yokohama National University in Japan, carried out experiments for the study at Berkeley Lab’s ALS in May 2016 with Aiko Nakato, a postdoctoral researcher at Kyoto University in Japan. Kilcoyne helped to train the researchers to use the ALS X-ray beamline and microscope.

    The beamline equipped with this X-ray microscope (a scanning transmission X-ray microscope, or STXM) is used in combination with a technique known as XANES (X-ray absorption near edge structure spectroscopy) to measure the presence of specific elements with a precision of tens of nanometers (tens of billionths of a meter).

    “We revealed that the organic matter was somewhat similar to that found in primitive meteorites, but contained more oxygen-bearing chemistry,” Kebukawa said. “Combined with other evidence, the results support the idea that the organic matter originated from a water-rich, or previously water-rich parent body – an ocean world in the early solar system, possibly Ceres.”

    Kebukawa also used the same STXM technique to study samples at the Photon Factory, a research site in Japan. And the research team enlisted a variety of other chemical experimental techniques to explore the samples’ makeup in different ways and at different scales.

    Chan noted that there are some other well-preserved crystals from the meteorites that haven’t yet been studied, and there are plans for follow-up studies to identify if any of those crystals may also contain water and complex organic molecules.

    3
    Ceres, a dwarf planet in the asteroid belt pictured here in this false-color image, may be the source of organic matter found in two meteorites that crashed to Earth in 1998. (Credit: NASA)

    Kebukawa said she looks forward to continuing studies of these samples at the ALS and other sites: “We may find more variations in organic chemistry.”

    The Advanced Light Source is a DOE Office of Science User Facility.

    Scientists at NASA Johnson Space Center, Kochi Institute for Core Sample Research in Japan, Carnegie Institution of Washington, Hiroshima University, The University of Tokyo, the High-Energy Accelerator Research Organization (KEK) in Japan, and The Graduate University for Advanced Studies (SOKENDAI) in Japan also participated in the study. The work was supported by the U.S. DOE Office of Science, the Universities Space Research Association, NASA, the National Institutes of Natural Sciences in Japan, Japan Society for the Promotion of Science, and The Mitsubishi Foundation.

    See the full article here .

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  • richardmitnick 2:00 pm on December 1, 2017 Permalink | Reply
    Tags: Astonomy Magazine, , Meteorites   

    From Astronomy: “The story of the fossil meteorites” 

    Astronomy magazine

    astronomy.com

    November 29, 2017
    David Boehnlein

    What four small pieces of rock can teach us about the history of the solar system.

    1
    An ancient meteorite sits embedded in a piece of limestone near the fossilized shell of a cephalopod. Courtesy Steve Zitowsky

    Visitors

    Imagine a traveler from outer space, hurtling through the atmosphere of a bright, blue planet to land upon a world populated by strange, multi-tentacled creatures. It sounds like something from the pages of a science fiction novel, but it’s a true story and it’s written in stone. The stone is at Chicago’s Field Museum of Natural History, one of four unusual slabs in a recently opened display of meteorites.

    At the time of the World’s Columbian Exposition in 1893, the collection of curiosities that would become the Field Museum included 170 meteorites. The museum now houses the Robert A. Pritzker Center for Meteoritics and Polar Studies, with a collection that includes more than 15,000 meteorites from over 1500 falls. “A fall,” explains Philipp Heck, associate curator of the Pritzker Center, “is an event in which the arrival of a meteorite is observed and recorded.” This allows fragments to be identified with that event. Meteorites not identified with a fall are known in the field of meteoritics as “finds.”

    The museum has pieces of many famous meteorites.There’s a thousand-pound remnant of the Canyon Diablo meteorite that gouged the great meteor crater in the Arizona desert.

    2
    Canyon Diablo iron meteorite (IIIAB) 2,641 grams. Note colorful natural patina. Image is missing a needed scale.
    Geoffrey Notkin, Aerolite Meteorites of Tucson Original uploader was Geoking42 at en.wikipedia

    There are fragments of the Chelyabinsk meteor, which made a fiery descent over Russia in 2014. There is even a meteorite that fell on a garage in Illinois in 1938, displayed alongside the holed seat and dented muffler of the car it struck. In a photograph taken shortly after the fall, the vehicle’s owner looks rather dismayed.

    But possibly the most intriguing meteorites in the collection are four that are embedded in slabs of limestone. They are surrounded by a whitish discoloration of the rock, evidence of something leaching from them. These are fossil meteorites. One of them, our aforementioned celestial visitor, rests only inches away from the mineralized shell of a cephalopod, an extinct mollusk related to the modern nautilus. Fossils of prehistoric sea creatures are common in rocks dating from the Ordovician Period, which lasted from 500 to 435 million years ago. But fossil meteorites are rare. In fact, they were unknown until 1952, when the first find was made in Sweden. To date, only 115 have been found, almost all of them at a single quarry.

    The Thorsberg Quarry

    Among the wooded hills along the southeast shore of Lake Vänern in southern Sweden, a line of rust-colored bluffs overlooks a smaller lake where limestone has been quarried for many years. This is the Thorsberg quarry, near the town of Kinnekulle. Striations in the stone there represent layers of sediment laid down over millions of years, when this place was at the bottom of an ancient sea. In that age there were no land animals or even true vertebrates; the first dinosaurs were still 230 million years in the future. Life was in the ocean, teeming with creatures now long gone. Trilobites scuttled along the sea floor and crinoids waved lazily with the movement of the water. Among them swam cephalopods of the genus Orthoceras, the apex predator, residing within a long, conical shell, tentacles groping for whatever luckless creature would become its next meal.

    This was the pattern of life in the Ordovician ocean; preserved by the long, slow process of fossilization to record a chapter in the history of life on Earth. But something extraordinary happened in the middle of the Ordovician Period. Meteorites began to fall among the future fossils, lots of them. As the meteorites settled into the sea floor, they were buried along with the remains of the sea creatures to become fossils themselves. And just as the fossilized animals tell a story about the history of life on Earth, the fossil meteorites relate a chapter in the history of the solar system.

    The L Chondrite Parent Body

    That story begins in the asteroid belt. The vast majority of meteorites that fall to Earth come from this ring of irregular, rocky bodies that never managed to form a planet. The asteroids occasionally jostle each other and when they do, the bits and pieces broken from them are sometimes sent Earthward. But 470 million years ago, there was a titanic collision among the asteroids. It shattered one of them completely in the biggest breakup the solar system has seen in the last 3 billion years. Immense amounts of debris from this collision were flung toward the inner solar system, where it quickly subjected Planet Earth to an intense bombardment. On a cosmic time scale, the number of meteorites falling to Earth jumped overnight. Scientists now refer to this doomed asteroid as the L Chondrite Parent Body (LCPB).

    3
    L Chondrite from Wikipdia

    That’s quite a story, but how can we know it’s true? After all, the trilobites didn’t leave us any observation logbooks. Nature, however, has left us a number of clues in the limestone beds of the Thorsberg quarry and in the meteorites themselves. Cosmochemistry is the study of the composition of materials in the universe and the processes that produced them. Like detectives tracking down a mystery, Heck and his colleagues have been using a combination of geology and cosmochemistry to piece together the story of the LCPB.

    The first step in proving the story is to verify that the objects found in the Thorsberg quarry are meteorites. “It’s not easy to identify a meteorite by just looking at it,” says Steve Zitowsky, who works in the Field Museum’s Pritzker Center. “People send us lots of items that they’ve found, thinking they might be a meteorite. Usually they’re not.” Zitowsky keeps the museum’s meteorite database up to date, weighing, measuring and photographing each new specimen. “I also found the critters,” he says with evident satisfaction, on examining the slabs with the fossil meteorites.

    Identifying fossils as meteorites also poses a special challenge. They’ve been buried and embedded in stone for hundreds of millions of years. Just as the seashells underwent a mineralogical change, turning to stone over the eons, so did the meteorites. The meteorites, of course, were already stone, but they underwent a process called diagenesis, which changes their mineral content. That’s what caused the whitish discoloration in the stone surrounding them. Researchers have to study their microscopic structure, along with their chemical composition, to be sure of their identity.

    The presence of the mineral chromite (FeCr2O4) in the fossils was one thing that identified them as meteorites. “Chromite is very resistant to diagenesis,” says Heck. Another important giveaway is the presence of chondrules: small, round particles found embedded inside the meteorite.

    4
    An ordinary chondrite meteorite displays the unique round “chondrules” that give this type of meteorite its name. James St. John.

    Types of Meteorites

    Although meteorites come in many varieties, there are three basic types: iron, stony iron, and stony. Stony meteorites are by far the most common, making up about 96 percent of those that fall to Earth. They are composed largely of silicate minerals, such as olivine and pyroxene. Iron meteorites, as the name suggests, are mostly iron, although they often contain other elements, such as nickel and cobalt. Stony irons, the most rare of the three types, combine the characteristics of the other two.

    The type of meteorite depends on where it came from in the parent body that broke apart to produce it. Some asteroids are differentiated — that is, they have an iron core surrounded by a rocky mantle and crust, just as Earth does. Differentiation occurs when a body is heated by collisions or radioactivity to the point where its materials can flow. The iron meteorites come from the core of such a body, stony irons from a narrow region between the core and mantle, and stony meteorites from the mantle and crust.

    Stony meteorites also come from asteroids that are not differentiated. Some asteroids were never hot enough to form an iron core, but did generate enough heat to melt bits of material embedded in them. These melted mineral grains are called chondrules and meteorites that contain them are called chondrites. Microscopic examination of the fossil meteorites shows that they are all chondrites.

    Having established that the embedded stones in the quarry are meteorites, and specifically that they are chondrites, can scientists go a step further in demonstrating that they all came from the same parent body? As a matter of fact, they can, because chondrites come in several varieties. The family of ordinary chondrites (there are also some not-so-ordinary ones that won’t be discussed here) includes three basic types: These are the H, L and LL chondrites. The H chondrites have a relatively high metal content; the L chondrites have a low metal content; and the LL chondrites have both a low metal content overall and a low iron content relative to other stony meteorites. Of the meteorites that fall to Earth today, 38 percent are L chondrites. In contrast, all of the fossil meteorites found to date are all L chondrites. They were the predominant type of meteorite in the Ordovician and moreover, they all came from the same asteroid, the L Chondrite Parent Body.

    The Million-Year Meteor Shower

    What happened after the LCPB disintegrated? The distribution of the meteorites in the quarry provides a clue. The limestone in which they are embedded was laid down as layers sediment over millions of years. The bottom layers are the oldest and the upper layers are the youngest. Geologists determine the ages of the layers by several methods. By applying sedimentation rates measured in modern environments, they can estimate how long it took to build up a layer. Index fossils, which are fossils of species known to have lived at a particular point in time, can pinpoint the age of a specific layer. There were many species of the mollusk Orthoceras and they are so common at Kinnekulle that the limestone is called orthoceratite. Finally, the decay products from natural radioactivity can date the rocks.

    A combination of these methods shows that the L chondrites began to arrive here just under 470 million years ago. And when they arrived, they came en masse. Birger Schmitz of the University of Lund in Sweden has been searching the Thorsberg quarry for fossil meteorites since 1993. The search has covered all of the old sea floor that has been quarried since then. “There is a clear and confirmed two-orders-of-magnitude increase in the flux of small meteorites to Earth,” says Schmitz. “The abundance of meteorites on the mid-Ordovician sea floor is far too high to be explained by a meteorite flux similar to that of today.” When the debris of the LCPB breakup began to reach this planet, meteorites fell with a frequency 100 times the modern rate for a million years. Furthermore, data from preserved craters indicates an order-of-magnitude increase in the flux of small asteroids as well. There must have been some spectacular meteor showers, but unfortunately nobody was there to see them.

    The L Chondrite Express

    Not only did the L chondrites bombard Earth in huge numbers, they did it very quickly. The typical travel time for a meteorite is millions to tens of millions of years. This is the time from when its parent body breaks apart to when a piece of it lands on Earth as a meteorite. The fossil meteorites, however, began to arrive mere tens of thousands of years after the breakup of the LCPB. “They came to us by express delivery,” says Heck.

    How is it possible to know how long a meteorite travelled through interplanetary space? There would have to be some kind of clock built into it. There is such a clock and the cosmochemists are able to read it by measuring the amount of certain rare isotopes of elements that are in the meteorite.

    The clock works like this: Every atom of every element has a mass number equal to the combined number of protons and neutrons in its nucleus. For example, helium with two protons and two neutrons has a mass number of 4 and is written as 4He. Likewise, an atom of neon normally has 10 protons and 10 neutrons and is denoted as 20Ne. In rare cases, a nuclear reaction can produce a nucleus with fewer or more neutrons than normal, resulting in isotopes like 3He (2 protons, 1 neutron) or 21Ne (10 protons, 11 neutrons). On Earth, naturally occurring neon has only about a quarter of a percent 21Ne; naturally occurring helium has a mere ten-thousandth of a percent 3He. These rare nuclei are produced by cosmic rays, the high-energy radiation that permeates outer space, and are called cosmogenic isotopes.

    While an asteroid is intact, the rock in its interior is shielded from the cosmic rays and cosmogenic isotopes are not produced. When the asteroid breaks apart, the fragments are exposed to cosmic rays and production of cosmogenic isotopes begins. When the fragment falls to Earth as a meteorite, it is shielded once again by Earth’s atmosphere and production of the cosmogenic isotopes stops. Thus, the quantity of cosmogenic isotopes in the meteorite provides a measure of how long it was travelling in space.

    Heck and his colleagues studied the fossil meteorites for cosmogenic isotopes of 3He and 21Ne, cross-checking the results against the layers of rock where they were found. Their remarkable result was that the older the rock layer, the less time the meteorites in it had spent in transit. This is basically the result you’d expect if all of the meteorites came from a single parent body, with the ones making the shortest trip sitting here longest. What is surprising, though, is just how little time it took them to get here. That celestial traveler mentioned at the beginning of the article spent a mere 50,000 years on its journey here, only 1 percent of the travel time of a typical meteorite. As if being embedded next to a cephalopod didn’t make it rare enough. The probable explanation for this rapid transit, says Heck, is that the breakup occurred near an orbital resonance, a spot where the gravity of Jupiter pulled them out of the asteroid belt and onto an Earthbound expressway.

    Meteorites Before the Breakup

    That’s a good deal of evidence to support the story of a cataclysmic collision of asteroids followed by a rain of L chondrites on Earth, yet there is still another way to check it. What about L chondrites before the breakup of the LCPB? We know that L chondrites dominated the meteorite flux in the mid-Ordovician, but today, they’re just over a third of the meteorites landing here. So another way to verify the story of a big burst of meteorites from the LCPB is to look at how common or rare L chondrites were in the early Ordovician Period. The problem is how to check for L chondrites when there are so few meteorites to be found. The answer is micrometeorites.

    Meteoritic material is constantly falling to Earth. The planet typically gains about five tons per year from meteorites, much of it in the form of tiny grains or microscopic fragments coming off of larger bodies. With the proper chemical methods, these micrometeorites can be recovered from the limestone. In a recent international study, scientists recovered micrometeorites from a Russian quarry and studied their isotopes to determine their type. They found that prior to 470 million years ago, most of the meteorites falling to Earth were achondrites; that is, stony meteorites with no chondrules. L chondrites were very rare. Once again, the LCPB story is verified.

    This sort of cosmochemical research, however, might go well beyond verifying the hypothesis of a single asteroid breakup. Schmitz has suggested that, just as geologists use strata of rocks and biologists use strata of fossils to describe the progression of Earth’s history, so might astronomers use meteoritic material to develop an astrostratigraphy that could add to our understanding of this history. Over the years, some scientists have conjectured that meteorites have been at least partially responsible for mass extinctions and subsequent evolutionary events. So far, only the Chicxulub Meteor, which struck at the end of the age of dinosaurs, is known to be associated with such an event.

    5
    This shaded relief image of Mexico’s Yucatan Peninsula show a subtle, but unmistakable, indication of the Chicxulub impact crater. Most scientists now agree that this impact was the cause of the Cretatious-Tertiary Extinction, the event 65 million years ago that marked the sudden extinction of the dinosaurs as well as the majority of life then on Earth.
    NASA/JPL-Caltech, modified by David Fuchs at en.wikipedia

    A more thorough understanding of fossilized meteorites and micrometeorites could further test such hypotheses.

    The Chicago L Chondrites

    The Field Museum has displayed its four fossil meteorites in a section that was added to the meteorite exhibit in early 2017. These are the only fossil meteorites in the western hemisphere, so they have a prominent place in the display. Even so, they’re not alone, because the LCPB isn’t quite finished with us yet.

    Just before midnight on March 26, 2003, residents of Park Forest, Illinois, were startled by what many thought was a bomb. Bright flashes in the sky, resounding booms and falling debris were reported throughout this Chicago suburb. It was, of course, a meteorite. Several homes were hit and one strike left the occupants looking up at a softball-sized hole in their ceiling. Fortunately, nobody was hurt. For the Chicago Center for Cosmochemistry at the nearby University of Chicago and for the Field Museum, the fall was a bonanza. When the fragments were collected and studied they were found to be L chondrites from the same source as the fossils in the Thorsberg quarry. Pieces of the Park Forest meteorite now reside in a display case alongside the fossil meteorites from Sweden. After 470 million years, they are reunited at last.

    6
    A piece of the Park Forest meteorite, also believed to have originated from the LCPB. James St. John

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  • richardmitnick 1:34 pm on May 3, 2017 Permalink | Reply
    Tags: Meteorites, , Vulcanism on Earth   

    From phys.org: “Ancient meteorite impact sparked long-lived volcanic eruptions on Earth” 

    physdotorg
    phys.org

    May 3, 2017

    1
    A photomicrograph of a vesicular green shard from the Onaping Formation of the Sudbury impact basin. Credit: Paul Guyett, Trinity College Dublin.

    Meteorite impacts can produce more than craters on the Earth – they can also spark volcanic activity that shapes its surface and climate by bringing up material from depth. That is the headline finding of an international team, led by geochemists from Trinity College Dublin, who discovered that large impacts can be followed by intense, long-lived, and explosive volcanic eruptions.

    The team studied rocks filling one of the largest preserved impact structures on the planet, located in Sudbury (Ontario, Canada). The ‘bolide’ hit the Earth here 1.85 billion years ago and excavated a deep basin, which was filled with melted target rocks and, later, with jumbled mixed rocks full of tiny volcanic fragments.

    Not only are there volcanic fragments throughout the sequence of the 1.5 km-thick basin but they have a very distinctive angular shape, which the scientists explain resembles a ‘crab claw’. Such shapes form when gas bubbles expand in molten rock that then catastrophically explodes—a feature of violent eruptions involving water, and which can be seen under glaciers in Iceland, for example. In the crater, these took place for a long period of time after the impact, when the basin was flooded with sea water.

    The key finding of the research, just published in the Journal of Geophysical Research: Planets, is that the composition of the volcanic fragments changed with time. Right after the impact, volcanism is directly related to melting of the Earth’s crust. However, with time, volcanism seems to have been fed by magma coming from deeper levels within the Earth.

    Professor of Geology and Mineralogy at Trinity, Balz Kamber, said: “This is an important finding, because it means that the magma sourcing the volcanoes was changing with time. The reason for the excitement is that the effect of large impacts on the early Earth could be more serious than previously considered.”

    On the early Earth there was a relatively brief period during which ca. 150 very large impacts occurred, whereas since then, only a handful have hit the Earth.

    Professor Kamber added: “The intense bombardment of the early Earth had destructive effects on the planet’s surface but it may also have brought up material from the planet’s interior, which shaped the overall structure of the planet.”

    The findings raise interest in topical research on similar volcanism on other planetary bodies like Mercury, Venus, Mars and the Moon. There, unlike on the Earth, the lack of plate tectonics and erosion help preserve surface features, which are probed by space craft.

    The insight from Sudbury is complemental, the geologists say, because you can directly observe the rocks with your own eyes and collect loads of samples for detailed study in the lab.

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  • richardmitnick 1:19 pm on February 2, 2017 Permalink | Reply
    Tags: , , Meteorites, Primitive achondrites,   

    From U Chicago: “Today’s rare meteorites were common 466 million years ago, study finds” 

    U Chicago bloc

    University of Chicago

    January 26, 2017
    Kate Golembiewski

    1
    Artist’s rendering of the space collision 466 million years ago that gave rise to many of the meteorites falling to Earth today.
    Illustration by Don Davis/Southwest Research Institute

    About 466 million years ago, there was a giant collision in outer space. Something hit an asteroid and broke it apart, sending chunks of rock falling to Earth as meteorites. But what kinds of meteorites were making their way to Earth before that collision?

    In a study published Jan. 23 in Nature Astronomy, scientists tackled that question by creating the first reconstruction of the distribution of meteorite types before the collision. They discovered that most of the meteorites falling to Earth today are rare, while many meteorites that are rare today were common before the collision.

    “We found that the meteorite flux—the variety of meteorites falling to Earth—was very, very different from what we see today,” said Philipp Heck, associate professor of geophysical sciences at the University of Chicago, the paper’s lead author. “Looking at the kinds of meteorites that have fallen to Earth in the last hundred million years doesn’t give you a full picture. It would be like looking outside on a snowy day and concluding that every day is snowy, even though it’s not snowy in the summer.”

    Meteorites are pieces of rock that have fallen to Earth from outer space. They’re formed from the debris of collisions between bodies like asteroids, moons and even planets. There are many different types of meteorites, which reflect the different compositions of their parent bodies. By studying the different meteorites that have made their way to Earth, scientists can develop a better understanding of how the basic building blocks of the solar system formed and evolved.

    “Before this study, we knew almost nothing about the meteorite flux to Earth in geological deep time,” said co-author Birger Schmitz, professor of nuclear physics at Lund University. “The conventional view is that the solar system has been very stable over the past 500 million years. So it is quite surprising that the meteorite flux at 467 million years ago was so different from (that of) the present.”

    To learn what the meteorite flux was like before the big collision event, Heck and his colleagues analyzed meteorites that fell more than 466 million years ago. Such finds are rare, but the team was able to look at micrometeorites—tiny specks of space-rock less than 2 millimeters in diameter that fell to Earth. They are less rare. Heck’s Swedish and Russian colleagues retrieved samples of rock from an ancient seafloor exposed in a Russian river valley that contained micrometeorites. They then dissolved almost 600 pounds of the rocks in acid so that only microscopic chromite crystals remained.

    Not having changed during hundreds of millions of years, the crystals revealed the nature of meteorites over time. Analysis of their chemical makeup showed that the meteorites and micrometeorites that fell earlier than 466 million years ago are different from the ones that have fallen since. A full 34 percent of the pre-collision meteorites belong to a meteorite type called primitive achondrites; today, only 0.45 percent of the meteorites that land on Earth are this type.

    Other micrometeorites sampled turned out to be relics from Vesta—the brightest asteroid visible from Earth, which underwent its own collision event over a billion years ago.

    Meteorite delivery from the asteroid belt to the Earth is a little like observing landslides started at different times on a mountainside, said co-author William Bottke, senior research scientist at the Southwest Research Institute. “Today, the rocks reaching the bottom of the mountain might be dominated by a few recent landslides. Going back in time, however, older landslides should be more important. The same is true for asteroid breakup events; some younger ones dominate the current meteorite flux, while in the past older ones dominated.”

    “Knowing more about the different kinds of meteorites that have fallen over time gives us a better understanding of how the asteroid belt evolved and how different collisions happened,” said Heck, an associate curator of meteoritics and polar studies at the Field Museum of Natural History. “Ultimately, we want to study more windows in time, not just the area before and after this collision. That will deepen our knowledge of how different bodies in our solar system formed and interact with each other.”

    Funding: European Research Council and Tawani Foundation

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  • richardmitnick 3:32 pm on September 2, 2016 Permalink | Reply
    Tags: , , , , Meteorites, Phosphorous, , Schreibersite   

    From astrobio.net via SETI: “Did meteorites bring life’s phosphorus to Earth?” 

    Astrobiology Magazine

    Astrobiology Magazine

    Aug 30, 2016
    Keith Cooper

    1
    An artist’s impression of meteors crashing into water on the young Earth. Did they bring phosphorous with them? Image credit: David A Aguilar (CfA)

    Meteorites that crashed onto Earth billions of years ago may have provided the phosphorous essential to the biological systems of terrestrial life. The meteorites are believed to have contained a phosphorus-bearing mineral called schreibersite, and scientists have recently developed a synthetic version that reacts chemically with organic molecules, showing its potential as a nutrient for life.

    Phosphorus is one of life’s most vital components, but often goes unheralded. It helps form the backbone of the long chains of nucleotides that create RNA and DNA; it is part of the phospholipids in cell membranes; and is a building block of the coenzyme used as an energy carrier in cells, adenosine triphosphate (ATP).

    Yet the majority of phosphorus on Earth is found in the form of inert phosphates that are insoluble in water and are generally unable to react with organic molecules. This appears at odds with phosphorus’ ubiquity in biochemistry, so how did phosphorus end up being critical to life?

    In 2004, Matthew Pasek, an astrobiologist and geochemist from the University of South Florida, developed the idea that schreibersite [(Fe, Ni)3P], which is found in a range of meteorites from chondrites to stony–iron pallasites, could be the original source of life’s phosphorus. Because the phosphorus within schreibersite is a phosphide, which is a compound containing a phosphorus ion bonded to a metal, it behaves in a more reactive fashion than the phosphate typically found on Earth.

    Finding naturally-formed schreibersite to use in laboratory experiments can be time consuming when harvesting from newly-fallen meteorites and expensive when buying from private collectors. Instead, it has become easier to produce schreibersite synthetically for use in the laboratory.

    Natural schreibersite is an alloy of iron, phosphorous and nickel, but the common form of synthetic schreibersite that has typically been used in experiments is made of just iron and phosphorus, and is easily obtainable as a natural byproduct of iron manufacturing. Previous experiments have indicated it reacts with organics to form chemical bonds with oxygen, the first step towards integrating phosphorous into biological systems.

    However, since natural schreibersite also incorporates nickel, some scientific criticism has pointed out that the nickel could potentially alter the chemistry of the mineral, rendering it non-reactive despite the presence phosphides. If this were the case it would mean that the experiments with the iron–phosphorous synthetic schreibersite would not represent the behavior of the mineral in nature.

    Since the natural version incorporates nickel, there has always been the worry that the synthetic version is not representative of how schreibersite actually reacts and that the nickel might somehow hamper those chemical reactions.

    “There was always this criticism that if we did include nickel it might not react as much,” says Pasek.

    Pasek and his colleagues have addressed this criticism by developing a synthetic form of schreibersite that includes nickel.

    2
    This 15cm wide fragment of the Seymchan meteorite found in Russia in 1967 is an iron-nickel pallasite. The long filament of dark grey material in the center is schreibersite. Image credit: University of South Florida.

    Nickel-flavored schreibersite

    In a recent paper published in the journal Physical Chemistry Chemical Physics, Pasek and lead author and geochemist Nikita La Cruz of the University of Michigan show how a form of synthetic schreibersite that includes nickel reacts when exposed to water. As the water evaporates, it creates phosphorus–oxygen (P–O) bonds on the surface of the schreibersite, making the phosphorus bioavailable to life. The findings seem to remove any doubts as to whether meteoritic schreibersite could stimulate organic reactions.

    “Biological systems have a phosphorus atom surrounded by four oxygen atoms, so the first step is to put one oxygen atom and one phosphorous atom together in a single P–O bond,” Pasek explains.

    Terry Kee, a geochemist at the University of Leeds and president of the Astrobiology Society of Britain, has conducted his own extensive work with schreibersite and, along with Pasek, is one of the original champions of the idea that it could be the source of life’s phosphorus.

    “The bottom line of what [La Cruz and Pasek] have done is that it appears that this form of nickel-flavored synthetic schreibersite reacts pretty much the same as the previous synthetic form of schreibersite,” he says.

    This puts to rest any criticism that previous experiments lacked nickel.

    3
    A bubbling hydrothermal pool in the Mývatn area of Iceland. Could such pools have pro-moted P–O bonds on the surfaces of schreibersite meteorites that had fallen into the pools? Image credit: Keith Cooper

    Shallow pools and volcanic vents

    Pasek describes how meteors would have fallen into shallow pools of water on ancient Earth. The pools would then have undergone cycles of evaporation and rehydration, a crucial process for chemical reactions to take place. As the surface of the schreibersite dries, it allows molecules to join into longer chains. Then, when the water returns, these chains become mobile, bumping into other chains. When the pool dries out again, the chains bond and build ever larger structures.

    “The reactions need to lose water in some way in order to build the molecules that make up life,” says Pasek. “If you have a long enough system with enough complex organics then, hypothetically, you could build longer and longer polymers to make bigger pieces of RNA. The idea is that at some point you might have enough RNA to begin to catalyze other reactions, starting a chain reaction that builds up to some sort of primitive biochemistry, but there’s still a lot of steps we don’t understand.”

    Demonstrating that nickel-flavored schreibersite, of the sort contained in meteorites, can produce phosphorus-based chemistry is exciting. However, Kee says further evidence is needed to show that the raw materials of life on Earth came from space.

    “I wouldn’t necessarily say that the meteoric origin of phosphorus is the strongest idea,” he says. “Although it’s certainly one of the more pre-biotically plausible routes.”

    Despite having co-developed much of the theory behind schreibersite with Pasek, Kee points out that hydrothermal vents could rival the meteoritic model. Deep sea volcanic vents are already known to produce iron-nickel alloys such as awaruite and Kee says that the search is now on for the existence of awaruite’s phosphide equivalent in the vents: schreibersite.

    “If it could be shown that schreibersite can be produced in the conditions found in vents — and I think those conditions are highly conducive to forming schreibersite — then you’ve got the potential for a lot of interesting phosphorylation chemistry to take place,” says Kee.

    Pasek agrees that hydrothermal vents could prove a good environment to promote phosphorus chemistry with the heat driving off the water to allow the P–O bonds to form. “Essentially it’s this driving off of water that you’ve got to look for,” he adds.

    Pasek and Kee both agree that it is possible that both mechanisms — the meteorites in the shallow pools and the deep sea hydrothermal vents — could have been at work during the same time period and provided phosphorus for life on the young Earth.

    Meanwhile David Deamer, a biologist from the University of California, Santa Cruz, has gone one step further by merging the two models, describing schreibersite reacting in hydrothermal fields of bubbling shallow pools in volcanic locations similar to those found today in locations such as Iceland or Yellowstone.

    Certainly, La Cruz and Pasek’s results indicate that schreibersite becomes more reactive the warmer the environment in which it exists.

    “Although we see the reaction occurring at room temperature, if you increase the temperature to 60 or 80 degree Celsius, you get increased reactivity,” says Pasek. “So, hypothetically, if you have a warmer Earth you should get more reactivity.”

    One twist to the tale is the possibility that phosphorus could have bonded with oxygen in space, beginning the construction of life’s molecules before ever reaching Earth. Schreibersite-rich grains coated in ice and then heated by shocks in planet-forming disks of gas and dust could potentially have provided conditions suitable for simple biochemistry. While Pasek agrees in principle, he says he has “a hard time seeing bigger things like RNA or DNA forming in space without fluid to promote them.”

    See the full article here .

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  • richardmitnick 10:27 am on August 29, 2016 Permalink | Reply
    Tags: Meteorites,   

    From TUM: “Meteorite Impact on a Nano Scale” 

    Techniche Universitat Munchen

    Techniche Universitat Munchen

    2016-08-29
    Prof. Friedrich Aumayr
    Institute of Applied Physics
    TU Wien
    Wiedner Hauptstraße 8-10, 1040 Wien
    T: +43-1-58801-13430
    friedrich.aumayr@tuwien.ac.at

    Dipl.-Ing. Elisabeth Gruber
    Institute of Applied Physics
    TU Wien
    Wiedner Hauptstraße 8-10, 1040 Wien
    T: +43-1-58801-13435
    elisabeth.gruber@tuwien.ac.at

    1
    Elisabeth Gruber in the lab at TU Wien

    2
    Nanostructures on a crystal after ion bombardment: Trenches with nanohillocks on either side are created. At the impact site, a particularly large nanohillock is formed.

    Intricate nanostructures can be created on crystal surfaces by hitting them with high energy ions. Scientists from TU Wien (Vienna) can now explain these remarkable phenomena.

    A meteorite impacting the earth under a grazing angle of incidence can do a lot of damage; it may travel a long way, carving a trench into the ground until it finally penetrates the surface. The impact site may be vaporized, there can be large areas of molten ground. All that remains is a crater, some debris, and an extensive trail of devastation on both sides of the impact site.

    Hitting a surface with high-energy, heavy ions has quite similar effects – only on a much smaller scale. At TU Wien (Vienna), Prof. Friedrich Aumayr and his team have been studying the microscopic structures which are formed when ions are fired at crystals at oblique angles of incidence.

    Trenches and Ridges

    “When we take a look at the crystal surface with an atomic force microscope, we can clearly see the similarities between ion impacts and meteorite impacts”, says Elisabeth Gruber, PhD-student in Friedrich Aumayrs team. “At first the projectile, scratching across the surface at a grazing angle, digs a trench into the crystal surface, which can be hundreds of nanometers long. Extensive ridges appear on either side of the trench, consisting of tiny structures called nanohillocks.” When the projectile ultimately enters the crystal and disappears, an especially large hillock is created at the impact site. Beyond that, the ion keeps moving below the surface, until it finally comes to a halt.

    This may sound simple and obvious, as if high energy ions just behaved like tiny, electrically charged bullets. But in fact, it is not at all self-evident that objects on a nano scale behave like macroscopic objects do. When atoms exchange energy, quantum physics always plays an important role.

    “When the high-energy ions interact with crystal surfaces – calcium fluoride, in our case – many different physical effects have to be taken into account”, says Friedrich Aumayr. “Electrons can change their energy state, they can exchange energy with atoms around them and excite vibrations in the crystal lattice, the so-called phonons. We have to carefully consider all these effects when we want to understand how the nanostructures on the crystal surface are created.”

    Melting and Evaporation

    In order to understand the mechanism leading to the nano-trenches and hillocks, the team developed extensive computer simulations, together with colleagues from Germany. “That way we can determine, how much different parts of the crystal surface are heated up”, says Elisabeth Gruber. “There are regions which become so hot that the material melts, at certain points it can even evaporate. When we know how large these regions are, we can predict very accurately what the nanostructures on the crystal surface will look like.”

    The goal of this line of research is not only to understand how tailored nanostructures can be created. It is also important to find out how different materials are harmed by heavy ion bombardment. “Calcium fluoride is often used as an insulator in semiconductor technology”, says Friedrich Aumayr. “We want our electronics to work, even under extreme conditions, for instance in a satellite which is exposed to cosmic radiation.” When the calcium fluoride layer is riddled with tiny holes, it can cause the device to short circuit and fail. Therefore, it is vital to understand the interaction of crystal surfaces and fast ions.

    Original publication:
    E. Gruber et al., Swift heavy ion irradiation of CaF2 – from grooves to hillocks in a single ion track 405001 Journal of Physics: Condensed Matter 28 (2016)

    See the full article here .

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    Techniche Universitat Munchin Campus

    Technische Universität München (TUM) is one of Europe’s top universities. It is committed to excellence in research and teaching, interdisciplinary education and the active promotion of promising young scientists. The university also forges strong links with companies and scientific institutions across the world. TUM was one of the first universities in Germany to be named a University of Excellence. Moreover, TUM regularly ranks among the best European universities in international rankings.

     
  • richardmitnick 9:51 am on October 17, 2015 Permalink | Reply
    Tags: , , Meteorites, Presolar grains,   

    From U Arizona: “Microscopic Findings, Astronomic Implications” 

    U Arizona bloc

    University of Arizona

    October 16, 2015
    Rebecca Peiffer NASA Space Grant Intern, University Relations – Communications

    1
    The arrow points to a grain of magnetite preserved from an ancient star, discovered by UA researcher Tom Zega and a team of researchers. (Photo: Tom Zega and © AAS. Reproduced with permission.)

    Imagine that you could travel back in time four and a half billion years ago, when the solar system was still just a bunch of rocks and dust and gas mixing together. Imagine watching all those billions of years of history re-created in front of you.

    Now, imagine that scientists are working to reconstruct this history with objects found here on Earth.

    One of the scientists is Tom Zega, an assistant professor in the University of Arizona’s Lunar and Planetary Laboratory. He studies “presolar grains,” which are the remains of ancient stars preserved in meteorites.

    These grains contain clues for scientists looking to build a narrative about the nearby stars before the birth of the solar system. Considering the scale of the undertaking, it is surprising that the evidence found in these presolar grains is microscopic.

    Scientists find the grains in chunks of meteorite mostly made up of rocks that formed after the solar system’s creation.

    “Those of us that are interested in understanding stardust basically have to find needles in the haystack,” Zega says.

    2
    The best samples of presolar grains come from meteorites found soon after their fall to Earth, so that any grains inside are not affected by rain or heat.

    To help find the needles, scientists employ some clever techniques.

    “We’ll take a chunk of a meteorite, we’ll boil it up in these harsh, nasty, aggressive acids, and then we’ll generate a residue,” Zega says.

    The process eliminates some of the excess meteorite and increases the chances of finding a presolar grain. The grains have endured millions of years of exposure to cosmic rays and maintained their original form, so some will withstand the acid and remain in the residue.

    Grains are only a few hundred nanometers wide. For context, a strand of human hair is 100,000 nanometers wide, and one nanometer is about half the width of a strand of DNA. To image the grains, scientists must use microscopes powerful enough to look at individual atoms.

    Through this procedure, Zega and a team of researchers discovered the first grain of magnetite with confirmed presolar origins and published their results in the Astrophysical Journal. From a sample only 650 nanometers wide, Zega estimated the size and chemical composition of its parent star, a star that inhabited this part of the galaxy before the solar system came into existence.

    Even the discovery of this grain was revealing. The chemical reaction that created the magnetite almost certainly required water vapor. This is one of the first experimental confirmations of water vapor around an ancient star.

    With the right approach, Zega says he believes presolar grains could even help construct a timeline for the history of our local part of the galaxy.

    “We know the galaxy itself is about 13 billion years old, and we know the solar system is four and a half billion years old, but there’s a lot of billions of years in between there for things to happen,” he says.

    If we could age-date these grains the way we age-date rocks on Earth, then we could start to document the astrophysical events that took place in this period. That’s one way studies of presolar grains can go beyond traditional observations through telescopes.

    With meteorites, researchers can do more than observe stardust — they can actually hold it in their hands.

    “It’s pretty amazing,” Zega says. “After 17 years in the field, I’m still fascinated by the fact that I can hold a piece of the solar system in my hand, and I can analyze it in the laboratory at the atomic level.”

    This excitement and curiosity inspires missions such as OSIRIS-REx, which aims to bring back samples of an asteroid for further study on Earth. For Zega and people in his field, that mission is like a dream come true.

    NASA Osiris -REx
    NASA/OSIRIS-REx

    “Everything that didn’t go into forming the sun or the planets was left over in the form of asteroids and meteors and dust,” he says. “So you can think of that as a time capsule that’s just sitting out there, and if we could we’d fly out there and grab samples of it. We’d rewrite the books.”

    For the next step in his research, Zega would like to collect more samples of presolar grains and look at the trends among them.

    That could help answer some of the big questions in planetary science about the origin of the solar system. In particular, the grains offer an estimate for how many stars injected their matter into the early solar system — and what kind of stars they were.

    “It just remains to be seen as time progresses whether we can come up with answers to some of these questions,” Zega says, smiling. “But we keep asking them.”

    See the full article here .

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    The University of Arizona (UA) is a place without limits-where teaching, research, service and innovation merge to improve lives in Arizona and beyond. We aren’t afraid to ask big questions, and find even better answers.

    In 1885, establishing Arizona’s first university in the middle of the Sonoran Desert was a bold move. But our founders were fearless, and we have never lost that spirit. To this day, we’re revolutionizing the fields of space sciences, optics, biosciences, medicine, arts and humanities, business, technology transfer and many others. Since it was founded, the UA has grown to cover more than 380 acres in central Tucson, a rich breeding ground for discovery.

    Where else in the world can you find an astronomical observatory mirror lab under a football stadium? An entire ecosystem under a glass dome? Visit our campus, just once, and you’ll quickly understand why the UA is a university unlike any other.

     
  • richardmitnick 12:45 pm on April 15, 2015 Permalink | Reply
    Tags: , , , Meteorites   

    From ANU: “Meteorites key to the story of Earth’s layers” 

    ANU Bloc

    Australian National University

    14 April 2015
    No Writer Credit

    1
    Dr Yuri Amelin. Image: Stuart Hay

    A new analysis of the chemical make-up of meteorites has helped scientists work out when the Earth formed its layers.

    The research by an international team of scientists confirmed the Earth’s first crust had formed around 4.5 billion years ago.

    The team measured the amount of the rare elements hafnium and lutetium in the mineral zircon in a meteorite that originated early in the solar system.

    “Meteorites that contain zircons are rare. We had been looking for an old meteorite with large zircons, about 50 microns long, that contained enough hafnium for precise analysis,” said Dr Yuri Amelin, from The Australian National University (ANU) Research School of Earth Sciences.

    “By chance we found one for sale from a dealer. It was just what we wanted. We believe it originated from the asteroid Vesta, following a large impact that sent rock fragments on a course to Earth.”

    The heat and pressure in the Earth’s interior mixes the chemical composition of its layers over billions of years, as denser rocks sink and less dense minerals rise towards the surface, a process known as differentiation.

    Determining how and when the layers formed relies on knowing the composition of the original material that formed into the Earth, before differentiation, said Dr Amelin.

    “Meteorites are remnants of the original pool of material that formed all the planets,” he said.

    “But they have not had planetary-scale forces changing their composition throughout their five billion years orbiting the sun.”

    The team accurately measured the ratio of the isotopes hafnium-176 and hafnium-177 in the meteorite, to give a starting point for the Earth’s composition.

    The team were then able to compare the results with the oldest rocks on Earth, and found that the chemical composition had already been altered, proving that a crust had already formed on the surface of the Earth around 4.5 billion years ago.

    The research is published in Proceedings of the National Academy of Sciences.

    See the full article here.

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  • richardmitnick 5:34 am on January 22, 2015 Permalink | Reply
    Tags: , Meteorites,   

    From Science 2.0: “Hidden Magnetic Messages From Space Discovered” 

    Science 2.0 bloc

    Science 2.0

    January 21st 2015

    Geologists have discovered hidden magnetic messages from the early solar system in meteorites measured using the PEEM-Beamline at the BESSY II synchrotron located in The Helmholtz-Zentrum Berlin für Materialien und Energie (HZB).

    Bessy II Synchrotron
    BESSY II synchrotron

    The information captures the dying moments of the magnetic field during core solidification on a meteorite parent body, providing a sneak preview of the fate of Earth’s own magnetic field as its core continues to freeze.

    Meteorites were previously thought to have poor magnetic memories, with the magnetic signals they carry having been written and rewritten many times during their long journey to Earth. [Dr. Richard] Harrison, however, identified specific regions filled with nanoparticles that were magnetically extremely stable. These “tiny space magnets” retain a faithful record of the magnetic fields generated by the meteorite’s parent body. Harrison and his colleagues could map these tiny magnetic signals using circular polarized X-ray synchrotron radiation at BESSY II.

    2
    The Pallasite meteorite, studied by Harrison, contains information about the early solar system. Image copyright Natural History Museum, London. Sample used from the Natural History Museum Meteorite Collection.

    Meteorites have witnessed a long and violent history; they are fragments of asteroids which formed in the early solar system, 4.5 billion years ago. Shortly after their formation, some asteroids were heated up by radioactive decay, causing them to melt and segregate into a liquid metal core surrounded by a solid rocky mantle. Convection of the liquid metal created magnetic fields, just as the liquid outer core of the Earth generates a magnetic field today. From time to time asteroids crash together and tiny fragments fall to Earth as meteorites, giving scientists the opportunity to study the properties of the magnetic fields that were generated billions of years ago. “They are like natural hard discs”, Dr. Richard Harrison believes. The geologist from the Department of Earth Sciences, University of Cambridge, UK, is searching for methods to decipher the information stored deep inside the space rocks. Now his new approach has yielded its first results.

    Until now it was not clear whether ancient magnetic signals could be retained by stony-iron meteorites at all. Large and highly mobile magnetic domains are found within the iron metal: these domains create huge magnetic signals but are easily overwritten by new events. The probability that these regions might contain useful information about early magnetic fields in the solar system is extremely low.

    But Harrison took a much closer look. At the PEEM-Beamline of BESSY II, Harrison and PhD student James Bryson found dramatic variation in magnetic properties as they went through the meteorite. They saw not only regions containing large, mobile magnetic domains, but also identified an unusual region called the cloudy zone containing thousands of tiny particles of tetrataenite, a super hard magnetic material. “These tiny particles, just 50 to 100 nanometers in diameter, hold on to their magnetic signal and don’t change. So it is only these very small regions of chaotic looking magnetization that contain the information we want”, Bryson concludes.

    The PEEM-Beamline offers X-rays with the specific energy and polarization needed to make sense of these magnetic signals. Since the absorption of the X-rays depends on the magnetization, the scientists could map the magnetic signals on the sample surface in ultrahigh resolution without changing them by the procedure. “The new technique we have developed is a way of analyzing these images to extract real information. So we can do for the first time paleomagnetic measurements of very small regions of these rocks, regions which are less than one micrometer in size. These are the highest resolution paleomagnetic measurements ever made”, Harrison points out.

    By spatially resolving the variations in magnetic signal across the cloudy zone, the team were able to reconstruct the history of magnetic activity on the meteorite parent body, and were even able to capture the moment when the core finished solidifying and the magnetic field shut down. These new measurements answer many open questions regarding the longevity and stability of magnetic activity on small bodies. Their observations, supported by computer simulations, demonstrate that the magnetic field was created by compositional, rather than thermal, convection – a result that changes our perspective on the way magnetic fields were generated during the early solar system and even provides a sneak preview of the fate of Earth’s own magnetic field as its core continues to freeze.

    Article: Long-lived magnetism from solidification-driven convection on the pallasite parent body, Nature on 22 January 2015. Source: Helmholtz-Zentrum Berlin für Materialien und Energie

    See the full article here.

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  • richardmitnick 3:09 pm on December 26, 2014 Permalink | Reply
    Tags: , , Meteorites   

    From ANL: “Earth’s most abundant mineral finally has a name” 

    News from Argonne National Laboratory

    December 11, 2014
    Tona Kunz

    An ancient meteorite and high-energy X-rays have helped scientists conclude a half century of effort to find, identify and characterize a mineral that makes up 38 percent of the Earth.

    And in doing so, a team of scientists led by Oliver Tschauner, a mineralogist at the University of Las Vegas, clarified the definition of the Earth’s most abundant mineral – a high-density form of magnesium iron silicate, now called Bridgmanite – and defined estimated constraint ranges for its formation. Their research was performed at the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility located at DOE’s Argonne National Laboratory.

    The mineral was named after 1946 Nobel laureate and pioneer of high-pressure research Percy [Williams] Bridgman. The naming does more than fix a vexing gap in scientific lingo; it also will aid our understanding of the deep Earth.

    To determine the makeup of the inner layers of the Earth, scientists need to test materials under extreme pressure and temperatures. For decades, scientists have believed a dense perovskite structure makes up 38 percent of the Earth’s volume, and that the chemical and physical properties of Bridgmanite have a large influence on how elements and heat flow through the Earth’s mantle. But since the mineral failed to survive the trip to the surface, no one has been able to test and prove its existence – a requirement for getting a name by the International Mineralogical Association.

    Shock-compression that occurs in collisions of asteroid bodies in the solar system create the same hostile conditions of the deep Earth – roughly 2,100 degrees Celsius (3,800 degrees Farenheit) and pressures of about 240,000 times greater than sea-level air pressure. The shock occurs fast enough to inhibit the Bridgmanite breakdown that takes place when it comes under lower pressure, such as the Earth’s surface. Part of the debris from these collisions falls on Earth as meteorites, with the Bridgmanite “frozen” within a shock-melt vein. Previous tests on meteorites using transmission electron microscopy caused radiation damage to the samples and incomplete results.

    So the team decided to try a new tactic: non-destructive micro-focused X-rays for diffraction analysis and novel fast-readout area-detector techniques. Tschauner and his colleagues from Caltech and the GeoSoilEnviroCARS, a University of Chicago-operated X-ray beamline at the APS at Argonne National Laboratory, took advantage of the X-rays’ high energy, which gives them the ability to penetrate the meteorite, and their intense brilliance, which leaves little of the radiation behind to cause damage.

    The team examined a section of the highly shocked L-chondrite meteorite Tenham, which crashed in Australia in 1879. The GSECARS beamline was optimal for the study because it is one of the nation’s leading locations for conducting high-pressure research.

    t
    Ordinary chondrite meteorite found in Queensland, Australia, 1879. On display in the Natural History Museum, London

    Bridgmanite grains are rare in the Tenhma meteorite, and they are smaller than 1 micrometer in diameter. Thus the team had to use a strongly focused beam and conduct highly spatially resolved diffraction mapping until an aggregate of Bridgmanite was identified and characterized by structural and compositional analysis.

    This first natural specimen of Bridgmanite came with some surprises: It contains an unexpectedly high amount of ferric iron, beyond that of synthetic samples. Natural Bridgmanite also contains much more sodium than most synthetic samples. Thus the crystal chemistry of natural Bridgmanite provides novel crystal chemical insights. This natural sample of Bridgmanite may serve as a complement to experimental studies of deep mantle rocks in the future.

    Prior to this study, knowledge about Bridgmanite’s properties has only been based on synthetic samples because it only remains stable below 660 kilometers (410 miles) depth at pressures of above 230 kbar (23 GPa). When it is brought out of the inner Earth, the lower pressures transform it back into less dense minerals. Some scientists believe that some inclusions on diamonds are the marks left by Bridgmanite that changed as the diamonds were unearthed.

    The team’s results were published in the November 28 issue of the journal Science as Discovery of bridgmanite, the most abundant mineral in Earth, in a shocked meteorite, by O. Tschauner at University of Nevada in Las Vegas, N.V.; C. Ma; J.R. Beckett; G.R. Rossman at California Institute of Technology in Pasadena, Calif.; C. Prescher; V.B. Prakapenka at University of Chicago in Chicago, IL.

    This research was funded by the U.S. Department of Energy, NASA, and NSF.

    See the full article here

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    Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation’s first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America’s scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science. For more visit http://www.anl.gov.

    The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit http://science.energy.gov/user-facilities/basic-energy-sciences/.

    Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science

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