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Scientists
reconstruct ancient impact that dwarfs dinosaur-extinction blast
Scientists
reconstruct ancient impact that dwarfs dinosaur-extinction blast
Date:
April 9,
2014
Source:
American Geophysical Union
Summary:
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.
......................
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 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 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.
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 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 Earth
during the tail end of the Late Heavy Bombardment period, a major period of
impacts that occurred early in Earth's history -- around 3 billion to 4 billion
years ago.
Many of the
sites where these asteroids landed were destroyed by erosion, movement Earth's
crust and other forces as 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 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 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 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 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.
Story
Source:
The above
story is based on materials provided by American Geophysical Union. Note: Materials may
be edited for content and length.
Journal
Reference:
- Norman H. Sleep, Donald R. Lowe. Physics of crustal fracturing and chert dike formation triggered by asteroid impact, ~3.26 Ga, Barberton greenstone belt, South Africa. Geochemistry, Geophysics, Geosystems, 2014; DOI: 10.1002/2014GC005229
Cite This
Page:
American Geophysical Union.
"Scientists reconstruct ancient impact that dwarfs dinosaur-extinction
blast." ScienceDaily. ScienceDaily, 9 April 2014. <www.sciencedaily.com/releases/2014/04/140409125851.htm>.
