Dinosaur-Killing Asteroid Traced to Breakup Event

Asteroid impact on Earth. i i

Researchers believe a fragment from the asteroid breakup created the 180-kilometer Chicxulub crater off the coast of the Yucatan Peninsula 65 million years ago. Don Davis hide caption

itoggle caption Don Davis
Asteroid impact on Earth.

Researchers believe a fragment from the asteroid breakup created the 180-kilometer Chicxulub crater off the coast of the Yucatan Peninsula 65 million years ago.

Don Davis
Map of asteroid impact progression. i i

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 hide caption

itoggle caption Courtesy of Southwest Research Institute
Map of asteroid impact progression.

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

The Rocky Details

  

A — A large asteroid approximately 170 kilometers in diameter was disrupted 160 million years ago when it was hit by another asteroid estimated to be 60 kilometers in diameter.

  

B — This impact produced what is now known as the Baptistina asteroid family, a cluster of asteroid fragments with similar orbits. The family originally included approximately 300 bodies larger than 10 kilometers and 140,000 bodies larger than 1 kilometer.

  

C — (1) Following the breakup event, the newly 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 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. About 2 percent of these main belt refugees hit the Earth, while a smaller fraction struck the Moon.

  

D — It is probable that a large fragment from 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

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.

The asteroid belt is a sort of rock pile in space for debris left over after the planets coalesced.

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.

"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 scientific journal Nature published Bottke's research this week.

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.

Geologist Phillipe Claeys of the Free University of Brussels in Belgium says the finding illustrates something people overlook about life on Earth.

"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.

In fact, we mammals may owe this asteroid a debt of thanks.

"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.

It's a coincidence that took 100 million years to play out, Bottke says, and one that should not be lost on the survivors.

"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.

So we're not out of the woods just yet.

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