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David Kring Colloquium Abstract (Feb 10, 2016)

Testing the Inner Solar System Impact Cataclysm

One of the intellectual legacies of the Apollo program is the lunar cataclysm hypothesis.  In a series of consortium studies (e.g., Cohen et al., Science 2000; Kring and Cohen, JGR 2002; Strom et al., Science 2005; Cohen et al., MAPS 2005; Puchtel et al., GCA 2008; Marchi et al., EPSL 2012; Joy et al., Science 2012; Morbidelli et al., EPSL 2012; Abramov et al., CdE 2013; Marchi et al., Nature Geoscience 2013; Marchi et al., Nature 2014) to test the lunar cataclysm hypothesis, evidence continues to support the concept of an intense period of bombardment several hundred million years after solar system formation.  Geologic, petrologic, geochemical, and isotopic data imply: (i) that basin-forming impacts occurred on the Moon ~3.9-4.0 Ga and that (ii) impacts occurred on asteroids ~3.6-4.1, implying the lunar cataclysm is an inner solar system cataclysm.  Geochemical fingerprints (iii) point to asteroids as the main source of debris hitting the Moon, while (iv) mineralogical and (v) geological fingerprints independently point to the main asteroid belt as the source of projectiles hitting the Moon, Mercury, and Mars, and also (vi) indicate the asteroid belt was sampled in a size-independent manner.  This suggests (vii) that resonances swept through the asteroid belt, which implies that (viii) Jupiter's orbit moved. Thus, analyses of the Moon are (ix) revealing details about the accretion and orbital evolution of planets in both the inner and outer solar system.  We have also been able to discern (x) collisions among asteroids that preceded the giant Moon-forming impact, (xi) deduced a possible age for the oldest and largest basin on the Moon, the South Pole-Aitken (SPA) basin, (xii) found that the SPA impact may have produced a magmatic epoch on the Moon, and (xiii) explored the consequences of impact cratering events on Earth throughout the Hadean.