Origins of a Species-Killer?

In case you missed this earlier this week, there was an intriguing detective science story that, if correct, has yielded remarkable news about the past of our planet, and of course, us. From an AP story by Richard Ingham (via Yahoo):

The extinction of the dinosaurs 65 million years ago can be traced to a collision between two monster rocks in the asteroid belt nearly 100 million years earlier, scientists report on Wednesday.

The smash drove a giant sliver of rock into Earth’s path, eventually causing the climate-changing impact that ended the reign of the dinosaurs and enabled the rise of mammals — including, eventually, us.

(Image above: Simulation images (AFP/HO/Don Davis) of the asteroid collision event, and the resulting extinction collision event on earth, and the collision with the moon.)

The scientists are William Bottke, David Vokrouhlicky and David Nesvorny, working at the Southwest Research Institute in Colorado. They traced the rock to a collision event that took place in the inner parts of the asteroid belt somewhere about between 140-190 million years ago, producing the family of fragments collectively called the Baptistinas, the largest being Baptistina 298. Over time, some of the fragments found their way out of the asteroid belt, and created a shower of rocks in the inner solar system. 65 million years ago, the scientist believe, one of them hit the earth, creating the famous event that changed the earth.

The trace of the great event, called the Cretaceous/Tertiary Mass Extinction, can be seen today in the shape of a 180-km (112-mile) -diameter impact crater at modern-day Chicxulub, in Mexico’s Yucatan peninsula.

The trio of researchers — William Bottke, David Vokrouhlicky and David Nesvorny of Southwest Research Institute in Colorado — took their theory a stage further and checked out sediment samples from the Chicxulub site.

They found traces of a mineral called carbonaceous chondrite, which is only found in a tiny minority of meteorites, as the earthly remains of plummeting asteroids are called. Most asteroids can be excluded from the Chicxulub event, but not Baptistina-era ones, they contend.

Putting simulation and chemical evidence together, the team rule out theories that a comet was to blame rather than an asteroid, and say there is a “more than 90 percent” probability that the killer rock was a refugee from the Baptistina family.

The investigators also put a 70-percent probability that a four-km (2.5-mile) Baptistina asteroid hit the Moon some around 108 million years ago, forming the 85-km (52-mile) crater Tycho.

And an interesting note:

The peak of “Baptistina bombardment” was probably around 100 million years ago but is not over yet, the paper cautions.

Many of the asteroids that skim dangerously close to Earth today owe their orbits to that great collision in the deep past, according to the authors.

-cvj