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Cosmic Impact Encourages Life To Go Forth and Multiply
By
Senior Science Writer
posted: 02:00 pm ET
08 March 2001
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Impacts accelerate evolution
The fossils of critters that emerged, survived and thrived in just 10,000 years now speak volumes about the tight relationship between life and cosmic catastrophe.
"It's clear when you look at the species before and after, that there are new [species] after the impact," Farley said. "Surely they've been culled from whatever population existed before the event. They haven't re-evolved from scratch. It shows how fast new species can populate a niche."
This rapid diversification of species is "particularly exciting because it implies that impacts might have accelerated the evolution of life on Earth," said Matthew Genge, a researcher at the London Natural History Museum.
Details in the dust
The chronology of death and rebirth was created by a steady supply of space dust that works its way to Earth from farther out in the solar system.
Asteroids located mostly between Mars and Jupiter, in a region known as the Asteroid Belt, bump and grind over time and create large amounts of dust. And comets that pass through the inner solar system release spurts of dust, which is spread through space over time.
These processes have been generating relatively consistent amounts of dust for many millions of years. Drawn toward the Sun by gravity, this dust captures and carries a high concentration of helium 3 that is riding outward from the Sun on the solar wind, a stream of energized particles.
The dust brings the helium 3 to Earth in miniscule but near-constant amounts. Some of it is stripped from the dust during entry into the atmosphere, but a steady fraction makes it to the surface. Genge, who studies the sources and effects of cosmic dust and meteorites, said using the dust to create a chronology is a very reliable method.
Comet or asteroid?
The new research might also shed light on the origin of the space rock that caused the extinction.
Genge said the findings suggest the impactor was not a "short-period" comet (like Comet Halley that regularly orbits the Sun). Periodic comets rarely spend more than a few tens of thousands of years in the inner solar system, explains Genge, before being swallowed by the Sun.
"We should see a gradual increase in the amount of helium 3 brought in by dust just before the impact and a decrease afterwards if it was a periodic comet," he told SPACE.com. "This is, therefore, evidence that the [Cretaceous-Tertiary] impactor was either an asteroid or a long-period comet."
Long-period comets originate as far as a third of the way to the nearest star in a halo of objects called the Oort Cloud, which surrounds our solar system. They can be tossed our way by the gravitational effects of passing stars.
More controversial claims have been made that these comets might be hurled Earthward by gravitational changes when our solar system passes through the dense plane of the Milky Way Galaxy, which it does periodically as we orbit around the galactic center.
Researchers have tried to tie this periodicity to an apparent cycle of mass extinctions occurring every 26 million years or so, though there is no agreement on the issue.
"It is thus interesting to ponder that if the position and motion of a planetary system controls the rate at which impacts occur, then it may also influence the biological evolution in habitable planetary environments," Genge said. "Too many impacts, and evolution may be stalled; too few, and it may only crawl along."
Click here for more new of astrobiology and asteroid impacts.
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