Deadly asteroid collision traced
2007-09-06 12:50
Paris - 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.
Other asteroid fragments smashed into the Moon, Venus and Mars, pocking their faces with mighty craters, the US and Czech researchers believe.
Mixing skills in time travel, jigsaw-making and carbon chemistry, the trio carried out a computer simulation of the jostling among orbital rubble left from the building of the Solar System.
The sleuths were guided by an intriguing clue - a large asteroid called (298) Baptistina, which shares the same orbital track as a group of smaller rocks.
Turning the clock back, the simulation found that the Baptistina bits not only fitted together, they were also remnants of a giant parent asteroid, around 170km across, that once cruised the innermost region of the asteroid belt.
Effect of collision 160m years ago
Around 160 million years ago - the best bet in a range of 140-190 million years - this behemoth was whacked by another giant some 60kms across.
From this soundless collision was born a huge cluster of rocks, including 300 bodies larger than 10kms and 140 000 bodies larger than one kilometre.
Over aeons, the fragments found new orbits with the help of something called the Yarkovsky effect, in which thermal photons from the Sun give a tiny yet inexorable push to orbiting rocks.
As the family gradually split up, a large number of chunks - perhaps one in five of the bigger ones - crept their way out of the asteroid belt and became ensnared by the gravitional pull of the inner planets.
Around 65 million years ago, a 10km piece crunched into Earth, unleashing a firestorm and kicking up clouds of dust that filtered out sunlight.
In this enduring winter, much vegetation was wiped out and the species that depended on them also became extinct. Only those animals that could cope with the new challenge, or could exploit an environmental niche, survived.
The trace of the great event, called the Cretaceous/Tertiary Mass Extinction, can be seen today in the shape of a 180km-diametre impact crater at modern-day Chicxulub, in Mexico's Yucatan peninsula.