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Distant space collision meant
doom for dinosaurs
Will Dunham
Reuters
Thursday September 6, 2007
A collision 160 million years ago of two asteroids orbiting between
Mars and Jupiter sent many big rock chunks hurtling toward Earth,
including the one that zapped the dinosaurs, scientists said on
Wednesday.
Their research offered an explanation for the cause of one of
the most momentous events in the history of life on Earth -- a
six-mile-wide (10-km-wide) meteorite striking Mexico's Yucatan
peninsula 65 million years ago.
That catastrophe eliminated the dinosaurs, which had flourished
for about 165 million years, and many other life forms, and paved
the way for mammals to dominate the Earth and the eventual rise
of humankind, many scientists believe.
The impact is thought to have triggered a worldwide environmental
cataclysm, expelling vast quantities of rock and dust into the
sky, unleashing giant tsunamis, sparking global wildfires and
leaving Earth shrouded in darkness for years.
(Article continues below)
U.S. and Czech researchers used computer simulations to calculate
that there was a 90 percent probability that the collision of
two asteroids -- one about 105 miles wide and one about 40 miles
wide -- was the event that precipitated the Earthly disaster.
The collision occurred in the asteroid belt, a collection of
big and small rocks orbiting the sun about 100 million miles from
Earth, the researchers report in this week's issue of the journal
Nature.
The asteroid Baptistina and rubble associated with it are thought
to be leftovers, the scientists said.
Some of the debris from the collision escaped the asteroid belt,
tumbled toward the inner solar system and whacked Earth and our
moon, along with probably Mars and Venus, said William Bottke
of the Southwest Research Institute in Boulder, Colorado, one
of the researchers.
DEADLY COLLISION
The collision is believed to have doubled for a while the number
of impacts occurring in this part of the solar system.
In fact, while the bombardment of this region of the solar system
due to this shower of debris peaked about 100 million years ago,
the scientists said the tail end of the shower continues to this
day. Bottke said many existing near-Earth asteroids can be traced
back to this collision.
"Imagine breaking up a big, big boulder on top of a hill
and all the fragments rolling down the hill. And somewhere at
the bottom is a village called Earth," Bottke said in a telephone
interview.
The dinosaur-destroying meteorite, thought to have measured 6
miles across, plunged into Mexico's Yucatan Peninsula and blasted
out the Chicxulub (pronounced CHIK-shu-loob) crater measuring
about 110 miles wide. The researchers looked at evidence on the
composition of this meteorite and found it consistent with the
stony Baptistina.
The researchers estimated that there also was about a 70 percent
probability that the prominent Tycho crater on the Moon, formed
108 million years ago and measuring about 55 miles
across, also was carved out by a remnant of the earlier asteroid
collision.
Philippe Claeys of Vrije Universiteit Brussel in Belgium, who
was not involved in the research, said by e-mail the findings
were "clear evidence that the solar system is a violent environment
and that collisions taking place in the asteroid belt can have
major repercussions for the evolution of life on Earth."
Bottke emphasized that point. "Dinosaurs were around for
a very long time. So the likelihood is they would still be around
if that event had never taken place," Bottke said.
"Was humanity inevitable? Or is humanity just something
that happened to arise because of this sequence of events that
took place at just the right time. It's hard to say."
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