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    Default Earth Infancy

    Asteroids boiled young Earth’s oceans, remnant rocks suggest

    Early evolution may have been altered by high temperatures

    By Thomas Sumner 7:00am, May 15, 2015



    BOILING SEAS Huge asteroid impacts around 3.3 billion years ago boiled Earth’s oceans, new research suggests. Condensing rock vapor from the impacts left spherical bits of rock the size of BB pellets in the rock record, shown. (Picture: D. Lowe)



    Asteroid impacts around 3.3 billion years ago may have created hell on Earth.

    Rocks left over from Earth’s adolescence suggest that giant impacts boiled the oceans billions of years ago, lowering the global sea level by tens of meters. The huge amounts of energy released during the impacts increased air temperatures to more than 500° Celsius for weeks and above water’s boiling point for more than a year, researchers report online May 7 in Geology. These dramatic events would have shaped the evolution of early life on Earth, says geologist Donald Lowe of Stanford University.

    “These impacts would have a profound influence on any life trying to evolve into more complex, low-temperature organisms,” says Lowe, the study’s lead author. “They’d keep getting whacked by these giant impactors and driven to extinction or near extinction.”


    Reference:
    Geologic record of partial ocean evaporation triggered by giant asteroid impacts, 3.29–3.23 billion years ago

    Donald R. Lowe1 and Gary R. Byerly2

    Abstract
    Although lunar studies suggest that large asteroid impact rates in the inner solar system declined to their present low levels at 3.8–3.7 Ga, recent studies in greenstone belts indicate that asteroids 20 km to 70+ km in diameter were still striking the Earth as late as 3.2 Ga at rates significantly greater than the values estimated from lunar studies. We here present geologic evidence that two of these terrestrial impacts, at 3.29 Ga and 3.23 Ga, caused heating of Earth's atmosphere, ocean-surface boiling, and evaporation of tens of meters to perhaps 100 m of seawater. Rapid ocean evaporation resulted in abrupt sea-level drops, erosion of the exposed sea floor, and precipitation of distinctive layers of laminated silica representing marine siliceous sinter. Such events would have severely affected microbial communities, especially among shallow-water and photosynthetic organisms. These large impacts profoundly affected Archean crustal development, surface environment, and biological evolution until 3.2 Ga, or even later.
    • Received 29 January 2015.
    • Revision received 31 March 2015.
    • Accepted 1 April 2015.
    1-Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA
    2-Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA
    Last edited by Hervé; 25th May 2015 at 01:00.
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    Default Re: Earth Infancy

    Quote Condensing rock vapor, from the impacts, left spherical bits of rock
    Now... that's HOT !

    This Ancient Asteroid Strike Was More Insane Than We Realized

    By George Dvorsky





    Around 3.26 billion years ago — long before the dinosaurs — a massive asteroid measuring nearly 36 miles (58 km) across smashed into the Earth. Geologists have now reconstructed this cataclysmic event, and it was far, far bigger than we thought. Here's how things went down on that fateful day.

    Thanks to geophysicists Norm Sleep and Don Lowe, here's what we now know.

    The Earth Shook for a Half Hour
    The impactor itself was somewhere between between 37 and 58 kilometers (23 to 36 miles) wide. That's about the width of Rhode Island and about three to five times larger than the asteroid thought to have wiped out the dinosaurs. When it struck the Earth, it was moving at 20 kilometers per second (12 miles per second).



    The collision instigated a planetary-wide earthquake measuring more than 10.8 on the Richter Scale. It propelled seismic waves hundreds of miles through the Earth, breaking rocks and setting off other large earthquakes. This earthquake shook the earth for a half hour — about six times longer than the one that struck Japan in 2011.

    The event also rebooted parts of the Earth's tectonic system. According to Lowe, who's studying geological features in a South African region known as the Barberton greenstone belt, the impact initiated the modern plate tectonic system that's now seen in the region. This is the first study to model an impact that occurred more than 3 billion years ago.

    Massive Tsunamis
    It also triggered tsunamis thousands of meters deep — far bigger than anything that could be generated by conventional earthquakes. These tsunamis swept across the oceans that covered most of the Earth at the time.


    The resulting crater was 300 miles across (500 km) — about the distance from Washington, D.C. to New York City.


    The Sky Burned and the Oceans Boiled
    The Earth's surface was completely fried. The sky became red hot, the atmosphere was filled with dust and debris — and the tops of the oceans boiled. Vaporized rock was shot up into the atmosphere where it circled the globe and condensed into liquid droplets before solidifying and falling back to the surface.

    The scientists say the event could have been one of dozens that struck the Earth during the tail end of the Late Heavy Bombardment period. Since that time, many of the impact sites have been covered as a result of erosion and other natural processes. But the geologists have found a number of areas in South Africa and Western Australia that contain evidence of the impact. Their best guess is that the asteroid struck an area thousands of kilometers away from the Barberton Greenstone Belt.

    Read the entire study at Geochemistry, Geophysics, Geosystems: "Physics of crustal fracturing and chert dike formation triggered by asteroid impact, ~3.26 Ga, Barberton greenstone belt, South Africa." Additional information via Stanford University.

    Images: Johan Swanepoel/Shutterstock | Stanford/Lowe&Sleep.
    Last edited by Hervé; 26th May 2015 at 15:59.
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    Default Re: Earth Infancy

    Earth's twin?

    Was the Moon born in a head-on collision?

    By Belinda Smith, deputy editor of Cosmos, 29 Jan 2016

    The high-speed crash that scientists think formed the Moon may have been less a side-swipe and more a head-on, Belinda Smith reports.



    A close-up of lunar rock from the Apollo 17 mission. Its oxygen 'fingerprint' matches that of Earth rocks.Credit: Paul Warren/UCLA

    As births go, they don’t come
    much more violent than the Moon's.

    Some 4.5 billion years ago, the young Earth collided with a developing planet, Theia. But instead of dealing each other a glancing blow, chemical analysis shows the collision was head-on, disintegrating Theia and part of Earth into a hot swirling disk of water and dust surrounding what was left of Earth.

    This mix eventually clumped together to become the Moon, a new study suggests.

    The key to the findings is the unique oxygen “fingerprint” that is found in all the planets, moons, comets and asteroids in our Solar System, including the Earth and the Moon.

    More than 99.9% of Earth’s oxygen is “normal”, with each atom containing eight protons and eight neutrons. But there are small quantities of slightly heavier oxygen – molecules with an extra neutron jammed in.

    While this "fingerprint" is a reliable identifier, it has traditionally been very hard to detect. So the University of California Los Angeles-led team used new, super-sensitive equipment to analyse seven lunar rocks brought back by the Apollo 12, 15 and 17 missions, as well as a lunar meteorite, and compared them to six volcanic rocks from the Earth’s mantle. They found their heavy oxygen levels to be almost identical – within five parts per million.

    To have that level of similarity, the planetary objects must have crashed into each other straight on. A side blow couldn’t account for that degree of mixing.

    “Theia was thoroughly mixed into both the Earth and the Moon, and evenly dispersed between them,” says study lead author and UCLA geochemist Edward Young, whose work is published in Science.

    “This explains why we don’t see a different signature of Theia in the Moon versus the Earth.”

    Had Theia side-swiped Earth instead, and become hooked into Earth’s orbit, most of the Moon would be made from Theia. It should, then, have a completely different oxygen fingerprint to Earth.

    But there is still one enduring question – just how big was Theia?

    Some, including Young, believe it was around the same size as Earth. Others think it was smaller, around the size of Mars. But had it not been wiped out in the Earth smash, Young says, it would probably have grown to become a planet.
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    Default Re: Earth Infancy

    Scientists reveal origin of Earth's oldest crystals


    Phys.org April 28, 2016


    Scanning electron microscope picture of a zircon crystal from the Sudbury crater. Credit: Gavin Kenny, Trinity College Dublin.

    New research suggests that the very oldest pieces of rock on Earth—zircon crystals—are likely to have formed in the craters left by violent asteroid impacts that peppered our nascent planet, rather than via plate tectonics as was previously believed.

    Rocks that formed over the course of Earth's history allow geologists to infer things such as when water first appeared on the planet, how our climate has varied, and even where life came from. However, we can only go back in time so far, as the only material we have from the very early Earth comes in the form of tiny, naturally occurring zircon crystals.

    Naturally then, the origin of these crystals, which are approximately the width of a human hair and more than four billion years old (the Earth being just over four and a half billion years old), has become a matter of major debate. Fifteen years ago these crystals first made headlines when they revealed the presence of water on the surface of the Earth (thought to be a key ingredient for the origin of life) when they were forming.

    Ten years ago, a team of researchers in the US1 argued that the ancient zircon crystals probably formed when tectonic plates moving around on the Earth's surface collided with each other in a similar fashion to the disruption taking place in the Andes Mountains today, where the ocean floor under the Pacific Ocean is plunging under South America.


    Shatter cones (pyramid-like structures) formed from the shock wave of the impact, and can be seen as that wave migrated through the rock from the bottom up. Credit: Gavin Kenny, Trinity College Dublin.

    However, current evidence suggests that plate tectonics—as we know it today—was not occurring on the early Earth. So, the question remained: Where did the crystals come from?

    Recently, geologists suggested these grains may have formed in huge impact craters produced as chunks of rock from space, up to several kilometres in diameter, slammed into a young Earth. To test this idea, researchers from Trinity College Dublin decided to study a much younger impact crater to see if zircon crystals similar to the very old ones could possibly have formed in these violent settings.

    In the summer of 2014, with the support of the Irish Reseach Council (IRC) and Science Foundation Ireland (SFI), the team collected thousands of zircons from the Sudbury impact crater, Ontario, Canada - the best preserved large impact crater on Earth and the planet's second oldest confirmed crater at almost two billion years old.

    After analysing these crystals at the Swedish Museum of Natural History in Stockholm, they discovered that the crystal compositions were indistinguishable from the ancient set.

    PhD Researcher in Trinity's School of Natural Sciences, Gavin Kenny, is first author of the article which explains these findings, and which has just been published in leading international journal, Geology.

    He said:
    Quote "What we found was quite surprising. Many people thought the very ancient zircon crystals couldn't have formed in impact craters, but we now know they could have. There's a lot we still don't fully understand about these little guys but it looks like we may now be able to form a more coherent story of Earth's early years—one which fits with the idea that our planet suffered far more frequent bombardment from asteroids early on than it has in relatively recent times."
    Gavin Kenny recently travelled to the annual Lunar and Planetary Science Conference (LPSC) in Houston, Texas, to present these findings to the space science community.

    He added:
    Quote "There was a lot of enthusiasm for our findings. Just two years ago a group2 had studied the likely timing of impacts on the early Earth and they suggested that these impacts might explain the ages of the ancient zircons. They were understandably very happy to see that the chemistry of the zircons from the Canadian impact crater matched the oldest crystals known to man."
    Explore further: Zircon crystals reveal onset of plate tectonics

    More information: Kenny GG, Whitehouse MJ, Kamber BS. Differentiated impact melt sheets may be a potential source of Hadean detrital zircon. Geology. 2016; DOI: 10.1130/G37898.1

    References:
    1: Watson EB, Harrison TM. Zircon thermometer reveals minimum melting conditions on earliest Earth. Science. 2005; 308:841-844. DOI: 10.1126/science.1110873

    2: Marchi S, Bottke WF, Elkins-Tanton LT, Bierhaus M, Wuennemann K, Mordibelli A, Kring DA. Widespread mixing and burial of Earth's Hadean crust by asteroid impacts. Nature. 2014; 511:578-582. DOI: 10.1038/nature13539

    Journal reference: Geology Science Nature
    Provided by: Trinity College Dublin

    Related:
    Oldest bit of crust firms up idea of a cool early Earth
    Study of isotopes shows recycling of Earth’s crust began 3 billion years ago
    Last edited by Hervé; 29th April 2016 at 01:02.
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    Default Re: Earth Infancy

    Clues to ancient giant asteroid found in Australia

    Date:May 16, 2016
    Source:Australian National University

    Summary:
    Scientists have found evidence of a huge asteroid that struck the Earth early in its life with an impact larger than anything humans have experienced. Tiny glass beads called spherules, found in north-western Australia were formed from vaporized material from the asteroid impact, 3.46 billion years ago.


    Marble Bar sediments, a microcrystalline silicone-rich chert. Credit: A. Glikson

    Scientists have found evidence of a huge asteroid that struck the Earth early in its life with an impact larger than anything humans have experienced.

    Tiny glass beads called spherules, found in north-western Australia were formed from vaporised material from the asteroid impact, said Dr Andrew Glikson from The Australian National University (ANU).

    "The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble," said Dr Glikson, from the ANU Planetary Institute.

    "Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago."

    The asteroid is the second oldest known to have hit the Earth and one of the largest.

    Dr Glikson said the asteroid would have been 20 to 30 kilometres across and would have created a crater hundreds of kilometres wide.

    About 3.8 to 3.9 billion years ago the moon was struck by numerous asteroids, which formed the craters, called mare, that are still visible from Earth.

    "Exactly where this asteroid struck the earth remains a mystery," Dr Glikson said.

    "Any craters from this time on Earth's surface have been obliterated by volcanic activity and tectonic movements."

    Dr Glikson and Dr Arthur Hickman from Geological Survey of Western Australia found the glass beads in a drill core from Marble Bar, in north-western Australia, in some of the oldest known sediments on Earth.

    The sediment layer, which was originally on the ocean floor, was preserved between two volcanic layers, which enabled very precise dating of its origin.

    Dr Glikson has been searching for evidence of ancient impacts for more than 20 years and immediately suspected the glass beads originated from an asteroid strike.

    Subsequent testing found the levels of elements such as platinum, nickel and chromium matched those in asteroids.

    There may have been many more similar impacts, for which the evidence has not been found, said Dr Glikson.

    "This is just the tip of the iceberg. We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds"

    "Asteroid strikes this big result in major tectonic shifts and extensive magma flows. They could have significantly affected the way the Earth evolved."

    The research is published in the journal Precambrian Research.


    Story Source:
    The above post is reprinted from materials provided by Australian National University. Note: Materials may be edited for content and length.

    Journal Reference:
    • Andrew Glikson, Arthur Hickman, Noreen J. Evans, Christopher L. Kirkland, Jung-Woo Park, Robert Rapp, Sandra Romano. A new ∼3.46Ga asteroid impact ejecta unit at Marble Bar, Pilbara Craton, Western Australia: A petrological, microprobe and laser ablation ICPMS study. Precambrian Research, 2016; 279: 103 DOI: 10.1016/j.precamres.2016.04.003
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    Default Re: Earth Infancy

    Earth's oldest rocks likely to have been created by meteorite bombardment

    PhysOrg
    Thu, 16 Aug 2018 18:08 UTC


    An example of rock from the Acasta River region of the NWT. © Pedroalexandrade/Wikimedia

    Scientists have found that 4.02 billion year old silica-rich felsic rocks from the Acasta River, Canada-the oldest rock formation known on Earth-probably formed at high temperatures and at a surprisingly shallow depth of the planet's nascent crust. The high temperatures needed to melt the shallow crust were likely caused by a meteorite bombardment around half a billion years after the planet formed. This melted the iron-rich crust and formed the granites we see today. These results are presented for the first time at the Goldschmidt conference in Boston tomorrow (14 August), following publication in the peer-reviewed journal Nature Geoscience.

    The felsic rocks (rocks rich in silica/quartz) found at the Acasta River in Canada, are the Earth's oldest rocks, although there are older mineral crystals. Scientists have long known that the Acasta rocks are different to the majority of felsic rocks we see today, such as the granites widely used as a building or decorative material. Now a group of scientists from Australia and China have modelled the formation of the oldest Acasta felsic rocks and found that they could only have been formed at low pressures and very high temperatures.


    © Google Maps

    Scientists believe that the primitive crust largely comprised dark, silica-poor mafic rocks, so there has been a question over how the Acasta River felsic rocks could have formed.
    "Our modelling shows that the Acasta River rocks derived from the melting of pre-existing iron-rich basaltic rock, which formed the uppermost layers of crust on the primitive Earth", said team leader Tim Johnson, from Curtin University, Perth.
    "We used phase equilibria and trace element modelling to show that the Acasta River rocks were produced by partial melting of the original mafic rocks at very low pressures. It would have needed something special to produce the 900°C temperatures needed to generate these early felsic rocks at such low pressures, and that probably means a drastic event, most likely the intense heating caused by meteorite bombardment.
    "We estimate that rocks within the uppermost 3km of mafic crust would have been melted in producing the rocks we see today. We think that these ancient felsic rocks would have been very common, but the passage of 4 billion years, and the development of plate tectonics, means that almost nothing remains.
    "We believe that these rocks may be the only surviving remnants of a barrage of extraterrestial impacts which characterized the first 600 million years of Earth History".
    The Acasta River is part of the Slave Craton formation in Northern Canada, north of Yellowknife and the Great Slave Lake. The area is the homeland of the Tlicho people, which led to the geologists who discovered the rocks giving them the name "Idiwhaa", derived from the Tlicho word for ancient.

    Commenting, Dr. Balz Kamber (Trinity College Dublin) said that
    "The idea of making felsic melts by large or giant impacts seems plausible considering the high-energy nature of these events and the pockmarked ancient surfaces of other inner Solar System planets and moons. However, the implied pressure-temperature regime might also permit melting of shallow crust below a super-heated impact melt sea. In other words, an indirect consequence of the impact itself".

    Reference:
    Tim E. Johnson, Nicholas J. Gardiner, Katarina Miljković, Christopher J. Spencer, Christopher L. Kirkland, Phil A. Bland & Hugh Smithies , An impact melt origin for Earth's oldest known evolved rocks, Nature Geoscience (2018). DOI: 10.1038/s41561-018-0206-5
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