NPR : Dinosaur-Killing Asteroid Traced to Breakup ...
http://www.npr.org/templates/story/story.php?stor...
September 18, 2007
Space
Dinosaur-Killing Asteroid Traced to Breakup Event
by Christopher Joyce
All Things Considered, September 5, 2007 · The reason humans rule the Earth
could be due to a huge collision that took place 160 million years ago.
Somewhere between Jupiter and Mars, two asteroids smashed into each other.
The debris hurtled into space, and eventually a big piece hit the Earth. This was
the asteroid that wiped out the dinosaurs and gave mammals a chance.
At least that's what a team of planetary scientists now claims.
Don Davis
Researchers believe a fragment from the
The asteroid belt is a sort of rock pile in space for debris left over after the planets
coalesced.
asteroid breakup created the 180-kilometer
Chicxulub crater off the coast of the Yucatan
Peninsula 65 million years ago.
The two asteroids that smashed together were big — one about 30 miles across,
the other more than three times that size. After the collision, rocky pieces
cart-wheeled off into space.
According to planetary scientist William Bottke, the gravitational pull of Mars
and Jupiter then acted as a sort of superhighway, guiding some of those
fragments toward the Earth.
"Think about a boulder on top of a big mountain, and you break up the boulder,
and all of a sudden, you create all these pieces and they start rolling down the
hill," Bottke says. "And somewhere at the bottom of the hill is some little village
called Earth and most pieces won't hit the Earth, but in some cases, they may
roll right through it."
Bottke, who works at the Southwest Research Institute in Colorado, says the
fragments from this collision doubled the rate of asteroid traffic in our neck of
the solar system for tens of millions of years.
And when he calculated their journey over that time, he realized that some
pieces would have intercepted our planet at a very important time in history.
This diagram from the Southwest Research
Institute shows how a large asteroid broke into
smaller ones. These smaller asteroids traveled
along a "superhighway" and over time,
eventually hit the Moon and Earth. Courtesy of
Southwest Research Institute
"We think we've found a very positive link between an impact event 65 million
years ago, which is believed to have wiped out the dinosaurs," Bottke says. "This
happened in the Yucatan Peninsula in a place called Chicxulub. That impact
appears to be linked to a very large fragment from our asteroid breakup, which is
one of the reasons we are very excited about this."
The Rocky Details
The scientific journal Nature published Bottke's research this week.
A — A large asteroid approximately 170
Bottke is 90 percent sure the killer asteroid came from this one "family" of
fragments. He notes this family has its own elemental "fingerprint" that
identifies its members as special — they are carbonaceous chondrites. That's the
same kind of rock that knocked off the dinosaurs.
kilometers in diameter was disrupted 160
million years ago when it was hit by another
asteroid estimated to be 60 kilometers in
diameter.
Geologist Phillipe Claeys of the Free University of Brussels in Belgium says the
1 of 2
18/09/2007 12:22
NPR : Dinosaur-Killing Asteroid Traced to Breakup ...
B — This impact produced what is now known
as the Baptistina asteroid family, a cluster of
asteroid fragments with similar orbits. The
http://www.npr.org/templates/story/story.php?stor...
finding illustrates something people overlook about life on Earth.
bodies larger than 10 kilometers and 140,000
bodies larger than 1 kilometer.
"The solar system is a very violent environment, and this is a very good example
of a collision taking place in the asteroid belt very far from us, but has a major
effect on the evolution of the biosphere on Earth," Claeys says.
C — (1) Following the breakup event, the newly
In fact, we mammals may owe this asteroid a debt of thanks.
family originally included approximately 300
formed fragments began to slowly migrate in
space by thermal forces produced when they
absorbed sunlight and re-radiated the energy
away as heat. (2) Over time, this gradual
spreading allowed about 20 percent of the
"Because without the collision, the dinosaurs might still be the dominant
organism of the planet, and we might still be crawling from one hole at night to
the other to feed ourselves," Claeys explains.
multi-kilometer-sized fragments to drift into a
nearby "superhighway" where their orbits were
modified enough to escape the main asteroid
belt. (3) Eventually, these fragments were
delivered to orbits that cross the Earth's path.
It's a coincidence that took 100 million years to play out, Bottke says, and one
that should not be lost on the survivors.
the Earth, while a smaller fraction struck the
Moon.
"We're still in the tail end of this asteroid shower, and this asteroid breakup will
continue to provide fragments to the inner solar system for an extended period of
time," Bottke says.
D — It is probable that a large fragment from
So we're not out of the woods just yet.
About 2 percent of these main belt refugees hit
this breakup event created the 85-kilometer
Tycho impact crater on the Moon 108 million
years ago.
E — It is even more likely that a still larger
fragment from the Baptistina breakup created
the 180-kilometer Chicxulub crater off the coast
of the Yucatan 65 million years ago. The
impact that produced this crater has been
strongly linked to the mass extinction event that
eliminated the dinosaurs.
Source: Southwest Research Institute
2 of 2
Related NPR Stories
March 30, 2007
Dinosaur Extinction and the Rise of Mammals
Feb. 8, 2006
T. Rex Had Humble Origins
March 13, 2007
NASA Report on Asteroids Suggests Nuclear Option
March 5, 2007
Scientists Gather at Conference to Stop Asteroids
18/09/2007 12:22