[Baps] EAPS talk today: Giant impacts, magma oceans and early Earth history

[Sarah Stewart-Mukhopadhyay]

EAPS Department Lecture<http://eapsweb.mit.edu/events/department-lecture-series>

*Sujoy Mukhopadhyay*

Associate Professor of Geochemistry
Harvard University
Department of Earth and Planetary Science

Wednesday, September 11, 2013
3:45 p.m. – 5:00 p.m.
54-915, Green Building Lecture Room

*Giant impacts, magma oceans and early Earth history*

Abstract: Earth’s violent accretion likely generated multiple magma oceans.
In particular, the Moon-forming giant impact is often thought to have
produced a whole mantle magma ocean, which would have homogenized any
pre-existing chemical heterogeneity within the mantle. The ratio of
primordial 3He to primordial 22Ne in the mantle preserves a record of magma
oceans on the early Earth. Importantly, the 3He/22Ne ratio of the Earth’s
shallow depleted mantle is significantly higher than the deep mantle. To
explain this observation, I propose that at least two giant impact-induced
atmospheric blow-off and magma ocean degassing episodes are required and
that the last giant impact did not generate a whole mantle magma ocean.
High-precision mantle Xe isotopic constraints indicate that the final
mantle outgassing and atmospheric blow-off events inferred from 3He/22Ne
ratios were accomplished between ~30 to 52 Myrs after the start of the
Solar System. Therefore, catastrophic outgassing associated with giant
impacts, including the Moon-forming impact, must have occurred within this
time window. Previous calculations of impact-induced atmospheric erosion
have, however, found that it is difficult to completely remove the
atmosphere from a body as large as Earth by a giant impact. The need for
atmospheric loss inferred from the noble gas data could be reconciled with
the dynamics of giant impacts by considering the new high-spin Moon
formation hypothesis.

A reception in Building 54, Room 923 precedes the talk.

http://eapsweb.mit.edu/events/2013/fall_DLS_Mukhopadhyay
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