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<a href="http://eapsweb.mit.edu/events/department-lecture-series" style="color:rgb(28,119,186);text-decoration:none">EAPS Department Lecture</a></h1><p style="margin-top:0px;font-size:0.92em;line-height:14px;color:rgb(0,0,0);margin-bottom:14px;font-family:Verdana,Tahoma,Arial,Lucida,Helvetica,'Bitstream Vera Sans',sans-serif">
<strong>Sujoy Mukhopadhyay</strong></p><p style="margin-top:0px;font-size:0.92em;line-height:14px;color:rgb(0,0,0);margin-bottom:14px;font-family:Verdana,Tahoma,Arial,Lucida,Helvetica,'Bitstream Vera Sans',sans-serif">
Associate Professor of Geochemistry<br>Harvard University<br>Department of Earth and Planetary Science</p><p style="margin-top:0px;font-size:0.92em;line-height:14px;color:rgb(0,0,0);margin-bottom:14px;font-family:Verdana,Tahoma,Arial,Lucida,Helvetica,'Bitstream Vera Sans',sans-serif">
Wednesday, September 11, 2013<br>3:45 p.m. – 5:00 p.m.<br>54-915, Green Building Lecture Room<br></p><p style="margin-top:0px;font-size:0.92em;line-height:14px;color:rgb(0,0,0);margin-bottom:14px;font-family:Verdana,Tahoma,Arial,Lucida,Helvetica,'Bitstream Vera Sans',sans-serif">
<strong>Giant impacts, magma oceans and early Earth history</strong></p><p style="margin-top:0px;font-size:0.92em;line-height:14px;color:rgb(0,0,0);margin-bottom:14px;font-family:Verdana,Tahoma,Arial,Lucida,Helvetica,'Bitstream Vera Sans',sans-serif">
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.</p>
<p style="margin-top:0px;font-size:0.92em;line-height:14px;color:rgb(0,0,0);margin-bottom:14px;font-family:Verdana,Tahoma,Arial,Lucida,Helvetica,'Bitstream Vera Sans',sans-serif">A reception in Building 54, Room 923 precedes the talk. </p>
<p style="margin-top:0px;font-size:0.92em;line-height:14px;color:rgb(0,0,0);margin-bottom:14px;font-family:Verdana,Tahoma,Arial,Lucida,Helvetica,'Bitstream Vera Sans',sans-serif"><a href="http://eapsweb.mit.edu/events/2013/fall_DLS_Mukhopadhyay">http://eapsweb.mit.edu/events/2013/fall_DLS_Mukhopadhyay</a><br>
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