[meteorite-list] meteorites from Earth Aw: Scientists Reconstruct Ancient, Massive Impact

From: Thomas Kurtz <Thomas.Kurtz_at_meteoritecentral.com>
Date: Thu, 10 Apr 2014 16:15:13 +0200
Message-ID: <trinity-4e949a3a-d8ab-438f-be2f-36fc44e9aaa4-1397139313608_at_3capp-gmx-bs54>

The question is:

Which achondrites have creation ages of 3.23 billion to 3.47 billion years ?
Perhaps we have material from this event among our collections.
Some material might still be flying in the solar system, even 3 billion years later.

Thomas Kurtz
Weil der Stadt, Germany

> Gesendet: Donnerstag, 10. April 2014 um 01:05 Uhr
> Von: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
> An: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
> Betreff: [meteorite-list] Scientists Reconstruct Ancient, Massive Impact
> http://news.agu.org/press-release/scientists-reconstruct-ancient-impact-that-dwarfs-dinosaur-extinction-blast/
> Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast
> American Geophysical Union
> Press Release
> 9 April 2014
> WASHINGTON, D.C. - Picture this: A massive asteroid almost as wide as
> Rhode Island and about three to five times larger than the rock thought
> to have wiped out the dinosaurs slams into Earth. The collision punches
> a crater into the planet's crust that's nearly 500 kilometers (about 300
> miles) across: greater than the distance from Washington, D.C. to New
> York City, and up to two and a half times larger in diameter than the
> hole formed by the dinosaur-killing asteroid. Seismic waves bigger than
> any recorded earthquakes shake the planet for about half an hour at any
> one location - about six times longer than the huge earthquake that struck
> Japan three years ago. The impact also sets off tsunamis many times deeper
> than the one that followed the Japanese quake.
> Although scientists had previously hypothesized enormous ancient impacts,
> much greater than the one that may have eliminated the dinosaurs 65 million
> years ago, now a new study reveals the power and scale of a cataclysmic
> event some 3.26 billion years ago which is thought to have created geological
> features found in a South African region known as the Barberton greenstone
> belt. The research has been accepted for publication in Geochemistry,
> Geophysics, Geosystems, a journal of the American Geophysical Union.
> The huge impactor - between 37 and 58 kilometers (23 to 36 miles) wide
> - collided with the planet at 20 kilometers per second (12 miles per second).
> The jolt, bigger than a 10.8 magnitude earthquake, propelled seismic waves
> hundreds of kilometers through the Earth, breaking rocks and setting off
> other large earthquakes. Tsunamis thousands of meters deep - far bigger
> than recent tsunamis generated by earthquakes - swept across the oceans
> that covered most of the Earth at that time.
> "We knew it was big, but we didn't know how big," Donald Lowe, a geologist
> at Stanford University and a co-author of the study, said of the asteroid.
> [Graphic]
> A graphical representation of the size of the asteroid thought to have
> killed the dinosaurs, and the crater it created, compared to an asteroid
> thought to have hit the Earth 3.26 billion years ago and the size of the
> crater it may have generated. A new study reveals the power and scale
> of the event some 3.26 billion years ago which scientists think created
> geological features found in a South African region known as the Barberton
> greenstone belt.
> Credit: American Geophysical Union
> Lowe, who discovered telltale rock formations in the Barberton greenstone
> a decade ago, thought their structure smacked of an asteroid impact. The
> new research models for the first time how big the asteroid was and the
> effect it had on the planet, including the possible initiation of a more
> modern plate tectonic system that is seen in the region, according to
> Lowe.
> The study marks the first time scientists have mapped in this way an impact
> that occurred more than 3 billion years ago, Lowe added, and is likely
> one of the first times anyone has modeled any impact that occurred during
> this period of the Earth's evolution.
> The impact would have been catastrophic to the surface environment. The
> smaller, dino-killing asteroid crash is estimated to have released more
> than a billion times more energy than the bombs that destroyed Hiroshima
> and Nagasaki. The more ancient hit now coming to light would have released
> much more energy, experts said.
> The sky would have become red hot, the atmosphere would have been filled
> with dust and the tops of oceans would have boiled, the researchers said.
> The impact sent vaporized rock into the atmosphere, which encircled the
> globe and condensed into liquid droplets before solidifying and falling
> to the surface, according to the researchers.
> The impact may have been one of dozens of huge asteroids that scientists
> think hit the Earth during the tail end of the Late Heavy Bombardment
> period, a major period of impacts that occurred early in the Earth's history
> - around 3 billion to 4 billion years ago.
> Many of the sites where these asteroids landed were destroyed by erosion,
> movement of the Earth's crust and other forces as the Earth evolved, but
> geologists have found a handful of areas in South Africa, and Western
> Australia that still harbor evidence of these impacts that occurred between
> 3.23 billion and 3.47 billion years ago. The study's co-authors think
> the asteroid hit the Earth thousands of kilometers away from the Barberton
> Greenstone Belt, although they can't pinpoint the exact location.
> "We can't go to the impact sites. In order to better understand how big
> it was and its effect we need studies like this,' said Lowe. Scientists
> must use the geological evidence of these impacts to piece together what
> happened to the Earth during this time, he said.
> The study's findings have important implications for understanding the
> early Earth and how the planet formed. The impact may have disrupted the
> Earth's crust and the tectonic regime that characterized the early planet,
> leading to the start of a more modern plate tectonic system, according
> to the paper's co-authors.
> The pummeling the planet endured was 'much larger than any ordinary earthquake,"
> said Norman Sleep, a physicist at Stanford University and co-author of
> the study. He used physics, models, and knowledge about the formations
> in the Barberton greenstone belt, other earthquakes and other asteroid
> impact sites on the Earth and the moon to calculate the strength and duration
> of the shaking that the asteroid produced. Using this information, Sleep
> recreated how waves traveled from the impact site to the Barberton greenstone
> belt and caused the geological formations.
> The geological evidence found in the Barberton that the paper investigates
> indicates that the asteroid was "far larger than anything in the last
> billion years," said Jay Melosh, a professor at Purdue University in West
> Lafayette, Indiana, who was not involved in the research.
> The Barberton greenstone belt is an area 100 kilometers (62 miles) long
> and 60 kilometers (37 miles) wide that sits east of Johannesburg near
> the border with Swaziland. It contains some of the oldest rocks on the
> planet.
> The model provides evidence for the rock formations and crustal fractures
> that scientists have discovered in the Barberton greenstone belt, said
> Frank Kyte, a geologist at UCLA who was not involved in the study.
> "This is providing significant support for the idea that the impact may
> have been responsible for this major shift in tectonics," he said.
> Reconstructing the asteroid's impact could also help scientists better
> understand the conditions under which early life on the planet evolved,
> the paper's authors said. Along with altering the Earth itself, the environmental
> changes triggered by the impact may have wiped out many microscopic organisms
> living on the developing planet, allowing other organisms to evolve, they
> said.
> "We are trying to understand the forces that shaped our planet early in
> its evolution and the environments in which life evolved," Lowe said.
> Notes for Journalists
> Journalists and public information officers (PIOs) of educational and
> scientific institutions who have registered with AGU can download a PDF
> copy of this article by clicking on this link:
> http://onlinelibrary.wiley.com/doi/10.1002/2014GC005229/abstract
> Or, you may order a copy of the final paper by emailing your request to
> Nanci Bompey at nbompey at agu.org. Please provide your name, the name of
> your publication, and your phone number.
> Neither the paper nor this press release is under embargo.
> Title
> "Physics of crustal fracturing and chert dike formation triggered by asteroid
> impact, ~3.26 Ga, Barberton greenstone belt, South Africa"
> Authors:
> Norman H. Sleep: Department of Geophysics, Stanford University, Stanford,
> CA, USA;
> Donald R. Lowe: Department of Geological and Environmental Sciences, Stanford
> University, Stanford, CA, USA.
> Contact information for the authors:
> Norman Sleep: +1 (650) 723-0882, norm at stanford.edu
> AGU Contact:
> Nanci Bompey
> +1 (202) 777-7524
> nbompey at agu.org
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Received on Thu 10 Apr 2014 10:15:13 AM PDT

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