Dinosaur-Killing Asteroid

Dinosaur-Killing Asteroid

Scientists have identified the event that probably created the asteroid that killed the dinosaurs.


The birth of a killer asteroid. I'm Bob Hirshon and this is Science Update.

65 million years ago, a six-mile-wide asteroid slammed into the Earth. This may have spelled doom for the dinosaurs. Now, a team of scientists has figured out where the killer asteroid may have come from.

Planetary scientist William Bottke of the Southwest Research Institute in Boulder, Colorado, says it was probably a fragment of a much larger asteroid called Baptistina—about 100 miles across—that had been shattered by a collision in outer space.


This breakup happened very close, almost right on top of, for lack of a better way to put it, a dynamical superhighway—an escape route out of the asteroid belt

—allowing some of the pieces to eventually cross Earth's path. The evidence comes from computer models, combined with chemical signatures that match the impact on Earth to Baptistina. I'm Bob Hirshon, for AAAS, the science society.

Making Sense of the Research

The cause of the dinosaurs' death has been debated for a long time, but presently, the evidence strongly suggests that this asteroid impact played a major role. And the asteroid definitely hit, because there's a giant crater in Chicxulub, Mexico—about 100 miles across—that dates back to that time in Earth's history. It would take an asteroid about six miles wide to leave a crater that size.

According to recent estimates by scientists at the University of Colorado, a hit from a six-mile wide asteroid would have created a blast equivalent to 100 megatons of TNT: enough to create a global firestorm that incinerated everything on land. Whatever life remained afterwards would have to contend with drastic aftershocks, including earthquakes and tidal waves, and the long-term climate change caused by dust and ash in the atmosphere. Although this is just one team's calculation, and some scientists believe that other factors also contributed to the dinosaurs' death, there's no denying that an asteroid impact like this would have been a literally earth-shaking event.

Bottke's model began when he was studying the present-day asteroid belt, a sort of space highway of asteroids orbiting the sun between Mars and Jupiter. Computer technology has allowed scientists to identify and categorize hundreds of thousands of these asteroids in the last decade. Some of these asteroids travel in tight clusters with very similar orbits; such clusters are believed to have come from large asteroids that shattered into many pieces hundreds of millions to billions of years ago.

Bottke and his colleagues identified a particular cluster of asteroids that hadn't been studied much yet. Scientists can use computer models and an understanding of the physical forces that affect asteroids to essentially rewind time and determine where these fragments might have come from. In this case, they traced the fragments back to a giant asteroid cluster, whose largest body is now called (298) Baptistina.

But there was more to the story. Bottke's team also noticed that the breakup of Baptistina occurred near an "escape route" out of the asteroid belt. In this region, the gravitational kicks produced by the planets, in this case Mars and Jupiter, can change the orbits of the fragments, enough to push some of them out of the asteroid belt and into Earth's path. (Actually, about 100 million years would pass between their escape from the asteroid belt and one asteroid's collision with Earth, but that's not so long on a geologic time scale).

In fact, their computer models, combined with the cratering record of the Earth, suggest that many fragments of Baptistina collided with Earth over a long period of time, but the impact of 65 million years ago was the most significant. What's more, over the past few years, scientists have analyzed and described the leftover remains of the asteroid that created the giant crater in Mexico. These trace materials turned out to be identical to a distinctive kind of meteorite falling on the earth today: carbonaceous chondrites. Remote sensing data suggests that the Baptistina fragments still in the asteroid belt are likely made of the same kind of distinctive material.

Using this information, Bottke's team developed a computer model to determine the probability that the alleged dinosaur-killing asteroid came from the Baptistina breakup. They concluded that this was about 90 percent likely. In addition, they determined that another large crater on the moon, called Tycho, dating back about 50 million years earlier, was 70 percent likely to have been created by another fragment of the Baptistina asteroid. And while there's some room for uncertainty, these numbers are pretty strong, considering how long ago all these events actually happened.

Now try and answer these questions:

  1. Why was the asteroid impact of 65 million years ago significant?
  2. How did Bottke's team connect that impact to the breakup of the Baptistina family?
  3. Describe the sequence of events, starting with the Baptistina breakup and ending with the extinction of the dinosaurs, as suggested by this research.
  4. Why is the chemical composition of the asteroid an important factor?

You may want to check out the October 26, 2007, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: chewing gum that's not sticky, worms and bacteria team up, some very hairy genetics, and more.

For Educators

The National Geographic Interactive feature Asteroids: Deadly Impact explores asteroids, meteors, and their impact on Earth. Click on the images to get started.

Read about other research on the impact in the National Geographic News articles Asteroid Rained Glass Over Entire Earth, Dinosaur-Killer Asteroid Imaged for First Time, and Fossil Leaves Suggest Asteroid Killed Dinosaurs.

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