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Applicant --Effects of Impact Bombardments on Early Earth and Mars

Wednesday, June 15, 2016

Abstract: Intense early cratering affected Earth and Mars by melting and fracturing their crusts, draping large areas in impact ejecta, generating regional-scale hydrothermal systems, and increasing atmospheric temperature and pressure. Post primary-accretionary bombardment scenarios that shaped early Earth and Mars can be imagined in two ways: either as a simple exponential decay with an approximately 100 Myr half-life, or as a “sawtooth” timeline characterized by both faster-than-exponential decay from primary accretion and relatively lower total delivered mass. Indications are that a late bombardment spike was superposed on an otherwise broadly monotonic decline subsequent to primary accretion, of which two types are investigated: a classical “Late Heavy Bombardment” (LHB) peak of impactors centered at ca. 3900 Ma that lasted 100 Myr, and a protracted bombardment typified by a sudden increase in impactor flux at ca. 4100–4200Ma with a correspondingly longer decay time (≤400Myr). Numerical models for each of the four bombardment scenarios cited above show that the terrestrial and martian crusts mostly escaped exogenic melting from bombardment. In this presentation, the effects of early impact bombardments on Earth and Mars will be compared and contrasted in terms of delivered energy, crustal melting, cratering density, resurfacing by crater formation and ejecta, impact-generated hydrothermal activity and habitable volumes.

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