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A collision 160 million years ago of two asteroids orbiting between Mars and Jupiter sent huge rock chunks hurtling toward Earth, including the one that zapped the dinosaurs.
Scientists have offered an explanation for the cause of one of the most momentous events in the history of life on Earth - a 10km-wide meteorite striking Mexico's Yucatan peninsula 65 million years ago.
That catastrophe eliminated the dinosaurs, which had flourished for about 165 million years, and many other life forms, and paved the way for mammals to dominate the Earth and the eventual rise of humankind, many scientists believe.
The impact is thought to have triggered a worldwide environmental cataclysm, expelling vast quantities of rock and dust into the sky, unleashing giant tsunamis, sparking global wildfires and leaving Earth shrouded in darkness for years.
United States and Czech researchers used computer simulations to calculate that there was a 90 per cent probability that the collision of two asteroids - one about 170km wide and one about 60km wide - was the event that precipitated the Earthly disaster.
The collision occurred in the asteroid belt, a collection of big and small rocks orbiting the sun about 180 million kilometres from Earth, the researchers report in this week's issue of the journal Nature.
The asteroid Baptistina and rubble associated with it are thought to be leftovers, the scientists say.
Some of the debris from the collision escaped the asteroid belt, tumbled toward the inner solar system and whacked Earth and our moon and probably Mars and Venus, said researcher William Bottke of the Southwest Research Institute in Boulder, Colorado.
The collision is believed to have doubled for a while the number of impacts in this part of the solar system.
And although the bombardment of this region of the solar system due to this shower of debris peaked about 100 million years ago, the scientists say the tail end of the shower continues to this day.
Dr Bottke said many existing near-Earth asteroids could be traced back to this collision. "Imagine breaking up a big, big boulder on top of a hill and all the fragments rolling down the hill. And somewhere at the bottom is a village called Earth."
The dinosaur-destroying meteorite hit the Yucatan Peninsula and blasted out the 180km-wide Chicxulub crater. Researchers found the meteorite's composition to be consistent with the stony Baptistina.
They estimated there also was about a 70 per cent probability that the prominent Tycho crater on the moon, formed 108 million years ago and measuring about 85km across, also was created by a remnant of the earlier asteroid collision.
"Dinosaurs were around for a very long time. So the likelihood is they would still be around if that event had never taken place," Dr Bottke said.
"Was humanity inevitable? Or is humanity just something that happened to arise because of this sequence of events that took place at just the right time. It's hard to say."
- Reuters
