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W. K. Hartmann (PSI)
Understanding of planetary surface evolution (and possibly biological evolution) is hampered by a longstanding uncertainty over the nature of impact cratering and interplanetary debris in the first 600 My of solar system history. On the one hand, a number of researchers (1-3) treat a cataclysmic spike in cratering 3.9 Gy ago as an observational fact, arguing that little or no cratering occurred from 4.5 to 4.0 Gy ago, and that all multi-ring lunar basins formed ~ 3.85 to 4.0 Gy ago. On the other hand, dynamical theorists have had problems trying to explain the a large impactor spike, as reviewed in (4). Worse yet, meteorite evidence on lunar and asteroidal impact melts (3,5) fail to confirm the strong spike in Apollo-sample impact melts at 3.9 Gy. A semi-quantitative model has been suggested to reconcile the findings (5).
References: (1) Tera, F., D.A. Papanastassiou, G. J. Wasserberg 1974. Isotopic evidence for a terminal Lunar cataclysm, Earth Planet. Sci. Lett. 22, 1-21. (2) Stoeffler, D., G. Ryder 2001. “Stratigraphy and Isotope Ages of Lunar Geologic Units: Chronological Standard for the Inner Solar System,” in Chronology and Evolution of Mars, Eds. R. Kallenbach, J. Geiss, W. K. Hartmann. Kluwer Academic Publishers, Netherlands, pp. 105-164. (3) Cohen, B. A., T. D. Swindle, D. A. Kring 2000. Support for the Lunar Cataclysm Hypothesis from Lunar Meteorite Impact Melt Ages. Science 290, 1754-1756. (4) Hartmann, W. K., G. Ryder, L. Dones, D. Grinspoon 2000. The Time-Dependent Intense Bombardment of the Primordial Earth/Moon System. In Origin of the Earth and Moon, Eds. R. M. Canup, K. Righter (Tucson: Univ. Arizona Press), pp. 493-512. (5) Hartmann, W. K. 2003. Megaregolith evolution and cratering cataclysm models – Lunar cataclysm as a misconception (28 years later). Meteor. Planet. Sci. 38, 579-593.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.