I often wonder if Iceland will turn out to be a huge impact crater? The present explanation appears more than ample but it is also plausible that an initiating impact triggered the ongoing separation of the two plates.
They are
clearly related and linked and may well represent a lot more than we
anticipate.
This item does
tell us just how severe the age of bombardment was. The Earth sponged up all the debris related
to its formation and that was like sucking up the asteroid belt which presently
lacks a large enough attractor and may be inside a zone of gravitational
instability
Scientists reconstruct ancient
impact that dwarfs dinosaur-extinction blast
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. 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] 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.
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