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SUMMARY:The last stage of Earth's formation: Increasing the pressure - Sim
 on Lock\, Harvard Univsersity
DTSTART:20171004T150000Z
DTEND:20171004T160000Z
UID:TALK80871@talks.cam.ac.uk
CONTACT:Sanne Cottaar
DESCRIPTION:The final stage of terrestrial planet formation is marked by h
 ighly energetic collisions between planetary sized bodies\, known as giant
  impacts. Giant impacts melt and vaporize substantial fractions of the col
 liding bodies and can leave the post-impact body rapidly rotating. Some fr
 action of giant impacts have sufficient energy and angular momentum (AM) t
 o produce a previously unrecognized planetary object\, called a synestia. 
 It has recently been suggested that our Moon was formed from a synestia cr
 eated by the last giant impact in Earth’s accretion. I will demonstrate 
 that the internal pressures of Earth-like planets do not increase monotoni
 cally during the giant impact stage\, but can vary substantially in respon
 se to changes in rotation and thermal state. The internal pressures in an 
 impact-generated synestia are much lower than in a condensed\, slowly rota
 ting planet of the same mass. For example\, the core-mantle boundary (CMB)
  pressure can be as low as 60 GPa for a synestia with Earth mass and compo
 sition\, compared to 136 GPa in the present-day Earth. The lower pressures
  are due to the low density and rapid rotation of the post-impact structur
 e. After the formation of the Moon from a synestia\, the internal pressure
 s in the interior of the synestia would have increased to present-day Eart
 h values in two stages: first by vapor condensation and second by removal 
 of AM from the Earth during the tidal evolution of the Moon. The pressure 
 evolution of the Earth has several important implications for its structur
 e and geochemistry\, which I will discuss.
LOCATION:Marine/Wolfson Building lecture hall\, Bullard Labs.
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