the Earth

Occasional killer asteroids could have spawned temporary rings of debris around Earth and played a major role in changing the world climate, according to scientists. Resembling the rocky halos that encircle Saturn, one such terrestrial ring might have chilled the globe considerably about 35 million years ago.

The geologic record indicates that Earth endured a brutal cold spell at the time, possibly sparked by a debris ring that persisted from 100,000 to several million years, the New Mexico researchers said.

Under certain conditions, if the angle and mechanics are just right, a big asteroid or comet could create a debris ring by slamming into Earth, scientists theorize.

Boslough, a physicist at the Sandia National Lab in Albuquerque, and colleague Peter Fawcett, an Earth sciences professor at the University of New Mexico, devised a climate model to predict the effects of such a disk.

Due to orbital mechanics, a halo of boulders and rocks would compress around the equator into a thin plane, much like the rings around Saturn and other planets in our solar system. The disk would reflect enough incoming sunlight to darken much of the tropics, which could set off large-scale weather changes as far away as the poles and chill the planet, the two said.

Boslough and Fawcett dug into the geologic record for supporting evidence. They found compelling clues dating back about 35 million years ago, when Earth could have weathered both a killer space rock collision and a prolonged big chill.

Geologic samples from the time contain iridium and melted rocks known as tektites, calling cards of major meteorite impacts. Moreover, sediments just above the iridium-tektite layer suggest Earth cooled for at least 100,000 years, the scientists said.

The time period, characterized by unusually cool winters, saw the demise of the horse in Europe and plankton in the Caribbean, according to scientists. The New Mexico researchers believe other transient rings have influenced global climate in the past.

Curiously, a much larger impact thought to have hastened the end of the dinosaurs about 65 million years ago probably failed to unleash a debris ring. The catastrophe wiped out the big lizards and almost all other species, but produced no long-term climate effects, they said.