WASHINGTON The mysterious disappearance of dinosaurs from the face of the planet 65 million years ago may have been caused by immense clouds of cosmic dust, the latest Science magazine says. An article in the issue which was due out Friday says colliding asteroids may have created both huge asteroid fragments and vast quantities of interplanetary dust that would have produced freezing temperatures and gradual mass extinctions lasting on the order of a million years.

During these dust-induced cold snaps the Earth would be at an abnormally high risk of asteroid impacts from the increased number ... of asteroid fragments, wrote Steve Kortenkamp, a Carnegie Institution scientist, and Stanley Dermott, a University of Florida astronomer. Any such impacts could augment the gradual extinctions caused by the dust, they wrote. A widely accepted theory for the extinction of the dinosaurs is a massive collision between the Earth and one single giant asteroid that hit Mexico. Kortenkamp and Dermott also attribute Earth's 100,000-year climate cycles to variations in the way in which the planet accumulates interplanetary dust.

The two scientists found that most of Earth's cosmic dust comes from three families of asteroids in the solar system's asteroid belt. As the Earth orbits the sun, it passes through this cloud of dust particles, capturing some of the dust in its atmosphere depending on the shape and tilt of the orbit. When the accretion of dust is at its peak, they wrote, substantial changes in Earth's climate could ensue, leading to the extinction of living species.

The consequences of such a scenario may be gradual mass extinctions lasting on the order of millions of years, some of which might be followed by or punctuated with single or multiple asteroid impacts, Kortenkamp and Dermott say. (AFP)