 |
|
 |
 advertisement
| |
|
|
|
|
|
Sudden Increase In Asteroid Impacts May Have Fueled Life
By Robert Roy Britt
Senior Science Writer
posted: 08:58 am ET
10 March 2000
|
Headline: Sudden Increase in Asteroid Impacts May Have Fueled Life In a finding that may impact everything from how life evolves to whether our sun has a companion star, researchers have found that the moon underwent a flurry of collisions from asteroids and comets between 400 million and 600 million years ago. The active period, which may still be going on, most likely affected Earth as well since both bodies are in roughly the same spot in the solar system, researchers said. The beginning of the busy stretch coincided with a rapid proliferation of life on Earth, suggesting a possible connection between catastrophe and evolution. Clues in the dirt Scientists found the clues not in the moons craters, but rather in tiny glass beads that were formed in the intense heat of impacts. The 155 smooth, round and mostly black beads involved in the study came from a single gram of soil that had been collected by the 1971 Apollo 14 crew. 
| A magnified view of glass bead, known as a spherule, from the Moon. |
By determining the beads ages, researchers estimated how often asteroids and comets hit the moon. Similar techniques would not work on Earth, because erosion and geologic processes destroy such ancient evidence. On the moon, however, there is no weather and little movement of the ground, so things pretty much stay put for eons. The data, reported in the March 10 issue of the journal Science, show that the impact crater creation rate -- which was high 3.5 billion years ago when large space rocks were being cleaned up by gravity in the fledgling solar system -- had dropped steadily until an unexpected rise 400 million to 600 million years ago. "It's a very significant increase," said Paul Renne, a UC Berkeley geologist involved in the study. There's also no reason to think the heightened pace of impacts isn't continuing, he added. But the causes behind the findings puzzle him a bit. "It's not straightforward as to why that might have happened," Renne told SPACE.com. It's possible, he said, that the larger space rocks of long ago are being recycled as smaller rocks, tens of kilometers in diameter on down to mere dust. Or, there could be some mechanism at work nobody has thought of. Richard Muller of UC Berkeley's Physics Department suggests that the sudden increase offers indirect evidence for a companion star to the sun, which was first suggested in 1984 and is sometimes called Nemesis, after the Greek goddess of retribution."The increase in impacts could be due to a sudden change in the orbit of Nemesis," said Muller, who also worked on the study. "If a passing star perturbed Nemesis into a more eccentric orbit, that would account for the increase in impacts." Implications for life The sudden increase coincides with the "Cambrian explosion," a period in which life on Earth took off with a dramatic burst in the number and diversity of species. "Although most people assume that impacts cause death and destruction, it is possible that the additional stress of the impacts forced life to become more diverse and flexible," Muller said. "Just as we stress trees, through pruning, to make them give more fruit, the stress caused by catastrophic impacts may have forced evolution into new directions." The researchers note that the earliest records of life coincide with the period when impacts first began to subside, 3.5 billion years ago, before ramping up again in the "recent" increase. "Maybe, as others have speculated before, life began on Earth many times, but the comets only stopped wiping it out about three or four billion years ago," Renne said. Timothy Culler, a UC Berkeley graduate student, was lead author on the report, which is expected to earn him his Ph.D.
|
|
|
|
|
|
 |
|
|
