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Science 10 March 2000:
Vol. 287. no. 5459, pp. 1785 - 1788
DOI: 10.1126/science.287.5459.1785
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Reports

Lunar Impact History from 40Ar/39Ar Dating of Glass Spherules

Timothy S. Culler, 13 Timothy A. Becker, 4* Richard A. Muller, 23*dagger Paul R. Renne 14*

Lunar spherules are small glass beads that are formed mainly as a result of small impacts on the lunar surface; the ages of these impacts can be determined by the 40Ar/39Ar isochron technique. Here, 155 spherules separated from 1 gram of Apollo 14 soil were analyzed using this technique. The data show that over the last ~3.5 billion years, the cratering rate decreased by a factor of 2 to 3 to a low about 500 to 600 million years ago, then increased by a factor of 3.7 ± 1.2 in the last 400 million years. This latter period coincided with rapid biotic evolutionary radiation on Earth.

1 Department of Geology and Geophysics,
2 Department of Physics, University of California, Berkeley, CA 94720, USA.
3 Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
4 Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA.
*   These authors are listed alphabetically.

dagger    To whom correspondence should be addressed. E-mail: ramuller{at}lbl.gov

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Isotopic Variability of Nitrogen in Lunar Regolith.
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Support for the Lunar Cataclysm Hypothesis from Lunar Meteorite Impact Melt Ages.
B. A. Cohen, T. D. Swindle, and D. A. Kring (2000)
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Time-Variable Cratering Rates?.
F. Horz, R. A. Muller, T. A. Becker, T. S. Culler, D. B. Karner, and P. R. Renne (2000)
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