Cosmic chain reaction led to death of dinosaurs, scientists say

The asteroid many believe caused the extinction of the dinosaurs some 65 million years ago has been traced to an earlier collision of larger asteroids about 95 million years earlier,scientists said Wednesday.

Writing in the scientific journal Nature, researcher William Bottke and co-authors laid out a scenario of the origin of the asteroid that landed on Earth in the Cretaceous Era, creating the enormous Chicxulub crater in Mexico's Yucatan peninsula.

Bottke, a researcher at the Southwest Research Institute in Boulder, Colo., said the collision of two asteroids between Jupiter and Mars about 160 million years ago set about a chain reaction that created a family of asteroids and sent fragments hurtling towards the sun.

Researchers said they were90 per cent certain that the Yucatan impact crater was caused by one of these fragments.

"We find that this asteroid shower is the most likely source of the Chicxulub impactor that produced the mass extinctionevent 65 million years ago," the scientists wrote in their paper.

The extinction of the dinosaurs, who had lived on Earth for about 165 million years, is seen as a turning point in the planet's history, a monumental occurrence that made it possible for mammalsto thrive.

The researchers came upon their discovery while analyzing the Baptistina family of asteroids in the asteroid belt between Mars and Jupiter, some 160 million kilometres from Earth.

Using computer simulations to trace the origin of this family of asteroids based upon their present movements, the researchers discovered the family was likely the result of a collision of two asteroids one about 60 km wide and the other 170 km wide.

The researchers speculate some of the fragments created during this collision gained enough energy to move out of their orbit and with the help of the gravitational pull of Mars and Jupiter were sent hurtling towards the Earth and other planets closer to the centre of the solar system.

The chemical composition ofpresent-day fragments in the Baptistina family match that of traces found at Chicxulub, the researchers say.

The collision theory also supports other evidence that has shown that the frequency of large-impact bodies hitting Earth and the moon rose by a factor of two over the long-term average during the last 100 million years, suggesting whatever event that led to the rise in space debris must have occurred before then, the scientists said.

The Earth was likely not the only object in our solar system to be hit by a remnant of the collision, the authors said.The large Tycho crater on the moon, formed 108 million years ago, was also likely caused from the initial impact, they wrote.