Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998lpico.957r...1a&link_type=abstract
Origin of the Earth and Moon, Proceedings of the Conference held 1-3 December, 1998 in Monterey, California. LPI Contribution N
Astronomy and Astrophysics
Astrophysics
Moon, Solar System, Lunar Evolution, Lunar Geology, Selenology, Meteorite Collisions, Planetary Geology, Terrestrial Planets, Lunar Orbits
Scientific paper
The late heavy bombardment of the Moon extends in time to about 3.8 Ga and continues to about 3.5 Ga with decreasing frequency of recorded impacts on the Moon. It has been generally assumed that this phenomenon was due to an invasion of the inner solar system by a swarm of asteroidal-sized objects that hit the Moon and all of the terrestrial planets with severeness in proportion to their gravitation. The extension of the record on Earth, and more fragmentarily on Mars, into this time frame demonstrates a lack of the predicted devastating effects. The sedimentary record on Earth consists of segments of undisturbed laminated banded-iron formations that contain traces of what appears as biochemically evolved microbial life. This record reaches back in time beyond 3.86 Ga The martian igneous rock record indicates a crystallization age of 4.5 Ga, followed by shock events but without signs of remelting in late bombardment catastrophes. These observations suggest, as one possibility, a local source of bodies in lunar orbit that coalesced with the Moon. Alternatively, solar-system-wide impacts may have been sufficiently sporadic to have escaped recording in currently studied sedimentary sequences on Earth. The latter alternative would have to be coupled with an assumption of rapid recolonization of the hydrosphere by life. It would than have arisen anew after each sterilizing impact or emerged from protected survival niches. These are speculations about of the absence of a recorded late planetary impact period. Current experiments that aim at resolution of this problem will be discussed.
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