Physics
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998lpico.957...12h&link_type=abstract
Origin of the Earth and Moon, Proceedings of the Conference held 1-3 December, 1998 in Monterey, California. LPI Contribution N
Physics
Earth-Moon System, Moon, Lunar Craters, Lunar Evolution, Earth Crust, Models, Planetary Evolution, Geochronology, Lunar Crust, Solar System Evolution
Scientific paper
The increase of the Earth-Moon system cratering rate prior to 3.8-4.0 Ma (relative to the present rate), has been documented from lunar data. If Earth's mass accumulated in about 50 m.y., as indicated by isotopic data, this gives one more data point on the curve of impact flux vs. time, at time = 4.5 Ga. The "initial impact flux" of 1 Earth mass in 50 m.y. gives a cratering rate of about l09 times the present rate. These data are internally consistent, because they fit decay rates of interplanetary debris being swept up by the newly formed planets. Thus, it is possible to make a model of the impact rate from about 4.5 to 3.9 Ma, declining with a gradually increasing half-life, and leveling out into a rate close to today's rate by about 3.5 Ma This model predicts extreme churning of the Earth's forming crust and chaotic disruption of the environment in the first few hundred million years. This model is also inconsistent with the proposal by Ryder that cratering was negligible for some period before about 3.9 Ga. Further work is needed to test, and choose between, these very different models.
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