Space dust 'did for dinosaurs'

An asteroid photographed by the robot spacecraft Galileo (Nasa)

Cosmic dust showering into the Earth's atmosphere could have set dinosaurs on the road to extinction long before the asteroid impact that is thought to have finished them off.

The theory is being advanced by scientists examining the effects of asteroids speeding through the solar system.

Researchers in the US believe that large amounts of space dust, which resulted from broken-up asteroids, could have started a global cooling process that gradually finished off the dinosaur age.

The claim still allows for the theory that dinosaurs were finally wiped out by a massive collision between the Earth and one single giant asteroid that hit the Yucatan peninsula.

The new theory, published in the latest edition of Science magazine, is the work of Stephen Kortenkamp, a planetary scientists at the Carnegie Institution, and Stanley Dermott, of the University of Florida.

Every year about 30,000 tonnes of space dust fall into the Earth's atmosphere without any serious effect, says Mr Kortenkamp.

These particles reflect sunlight, effectively shading the Earth and causing some cooling.

Orbit changes

But the amount can drastically increase depending on the Earth's eccentric orbit, which changes slightly from a circle to oval every 100,000 years.

As the orbit changes, the Earth passes through dense dust clouds and can pick up as much as 10 million tonnes of dust a year.

"That is comparable to what we know is injected into the atmosphere by a large volcano, and we know volcanoes have affected the climate," said Mr Kortenkamp.

Nuclear winter

That much matter could cause a "nuclear winter" whereby a pall of dust would block out so much sun that temperatures would drop, causing ice caps to grow and much plant and animal life to die off.

Mr Kortenkamp and Mr Dermott used computer models based on a collection of observations on Earth to formulate their theory.

The good news, according to the pair, is that a heavy dust build-up always precedes a major asteroid impact by about a million years, giving plenty of warning.

Mr Kortenkamp concedes that their findings have no immediate implications for humanity, although it is of great geological interest.