August 13, 2001 – Like homicide detectives searching for a mass murderer, scientists are trying to find the culprit behind one of the biggest killings in Earth's history.

A mass extinction 200 million years ago wiped out many of the species on the planet and helped crown the dinosaurs as the rulers of the world.

Using old-fashioned sleuthing aided by modern techniques, scientists have found tantalizing evidence suggesting that the impact of an asteroid or comet was the cause of the calamity at the boundary between the Triassic and Jurassic periods during the Mesozoic era.

"The Triassic-Jurassic boundary wiped out the competitors to the dinosaurs. It's only after the boundary that you get a dinosaur-dominated ecosystem," said Columbia University paleontologist Paul Olsen, a leading expert on dinosaurs of this period. "It's really quite a dramatic change."