University of Florida

By Kristen Vecellio

May 7, 1998


GAINESVILLE -- Space dust in the earth's atmosphere and changes in the planet's orbit may have started the gradual extinction of dinosaurs and other life thousands of years before a massive asteroid collision dealt the final blow, according to research from the University of Florida and the Carnegie Institution of Washington.

The dust build-up, which rises and falls on about a 100,000-year cycle, also may answer some big questions researchers have about the history of earth's climate, said Stanley Dermott, chairman of UF's astronomy department.

"A major, outstanding problem in present day geophysics is understanding the history of earth's climate," said Dermott.

The research is published in the May 8, 1998 issue of the journal Science.

The earth's climate varies on a 100,000 year scale, and during that time the earth's eccentricity changes causing the earth to move closer or farther away from the sun. Current scientific thinking says this variation in the amount of sunlight reaching the earth, known as the Milankovich Effect, changed the earth's climate.

But Dermott and Stephen Kortenkamp, a postdoctoral fellow at the Carnegie Institution, both felt this assumption was unlikely.

"The amount of variation is extremely small," Dermott said.

Dermott and Kortenkamp did calculations spanning 1.2 million years to prove the amount of dust in the atmosphere did vary and that the eccentricity of Earth's orbit can make dust accumulation rates vary by a factor of 2 or 3. Dermott said the earth gains nearly 30 million kilograms of dust a year, and the amount of dust in the atmosphere could effect earth's climate.

However, Dermott said, even that amount of dust is relatively small, so scientists still aren't sure exactly how much it could influence the climate.

Earth accumulates dust through gravitational focusing, an effect that causes the earth to pull dust particles toward it. To gather information on dust levels, NASA launched a craft the size of a school bus into the earth's atmosphere and counted the number of particle impacts on the side of the craft over several years. "It was a good record of the impact of dust striking earth," said Dermott.

Kortenkamp, a UF graduate, said the effects of interplanetary dust on the climate will be similar to the effects of volcanic dust in the atmosphere. Past volcanic eruptions have caused a detectable cooling of the earth's surface. Volcanic dust settles in a couple of months and the cooling effect is short-term.

But the effects of space dust on the atmosphere can last much longer. "The influx of interplanetary dust could remain at high levels for extended periods several hundred thousand years and therefore any associated cooling would also persist for this length of time," said Kortenkamp.

The researchers also examined the possibility that if the amount of dust in earth's atmosphere altered the climate, the change could cause gradual extinctions.

Dermott said every 100 million years the majority life on earth is destroyed by a catastrophic event, such as an asteroid striking Earth's surface, but history doesn't show an exact moment or date in time for the extinction of life.

Dermott and Kortenkamp are investigating the idea that if atmospheric dust effects the climate, then the dust may effect life on earth as well. For example, an asteroid collision creates a dust wave that reaches earth 1 million years before the asteroid. The dust may alter the climate enough to cause a gradual extinction before the asteroid hits earth's surface and causes a catastrophic event.

"While the issue is controversial, there are groups of paleontologists who have found evidence suggesting some mass extinctions were gradual, lasting for hundreds of thousands of years," Kortenkamp said.

To prove their theory, Kortenkamp said, a detailed analysis must be done of geological records looking for enhanced dust accumulation connected with gradual mass extinctions.

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