Meteoroid bombardment of moon has intensified in past
500 million years, coinciding with blossoming of life on

(Press Release Science 3 mar 2000)

The world-renown journal " Science "published recently a study which indicates that, timewise, meteoroid impacts on the moon is correlated with blossoming of life on Earth

" By dating minute glass beads thrown out by impacts over the millennia ", said Robert Sanders, Dept. of Public Affairs of UC Berkeley, " scientists at the University of California, Berkeley, and the Berkeley Geochronology Center have not only confirmed expected intense meteor activity 4 to 3.5 billion years ago, when the large lunar seas were formed, but have discovered another peak of activity that began 500 million years ago and continues today.

The tapering off of the first peak of activity, which probably included many large comets and asteroids, coincides with the earliest know evidence of life on Earth. The second and ongoing peak, which from the evidence seems to have been mostly smaller debris, began around the time of the great explosion of life known as the Cambrian ".

" The first life on Earth arose just after this real crescendo around 3.5 billion years ago, " said Paul R. Renne, adjunct professor of geology and geophysics at UC Berkeley and director of the Berkeley Geochronology Center. " Maybe life began on Earth many times, but the meteors only stopped wiping it out about 3 billion years ago. "

On another hand, Richard A. Muller, a professor of physics at UC Berkeley and a research physicist at Lawrence Berkeley National Laboratory, states "It's not surprising that the impacts tapered off about 3 billion years ago. The solar system was just getting cleaned up, primarily by Jupiter and the Sun. What is surprising is the reversion from a benign to a violent solar system about 500 million years ago. This work opens up a new field that tells us something about the history of our solar system that was totally unanticipated. Until now we did not realize how peculiar the past 500 million years has been."

Though all the Berkeley researchers agree on the new impact chronology for the moon, they have their own ideas about its implications. Renne, for example, leans toward the theory that interstellar dust seeded the Earth with organic molecules, from water to amino acids, that were incorporated into life on Earth during the past 500 million years.

Culler, the graduate student who originated the project under the supervision of Muller and Renne, sees the intense meteor activity as evidence that large meteor impacts played a major role in the evolution and extinction of life.

Muller too emphasizes the role impacts have played in the history of life on Earth. " It's not surprising that the recent intense period of meteor activity coincides with the rapid radiation of life on Earth ", he said.

According to Muller, a possibility exist that the sun could have a yet unknown companion star. This companion, he calls " Nemesis " would orbit the sun every 26 million years and periodically knocks comets out of their orbits, sending them hurtling toward the inner solar system. Muller also proposed that periodic climate changes are the result of the Earth's orbit periodically tilting up out of the orbital plane of the planets and intersecting a cloud of dust, debris and meteoroids.

Though the dating method was not sensitive enough to reveal a 26 million-year cycle in the impact record, "these findings fit in nicely with the Nemesis theory, " Muller said. " I think most of the debris came from perturbations in the outer solar system by Nemesis. "


Taken from:

Yves, Cons. Gen.

May 2000

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