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Unformatted text preview: The History of Earth and Life Lecture 12 1 Lecture 12 - The Early Earth The Early Earth The Hadean (the earliest time interval) The earliest half a billion years of the Earth's history From the time of Earth's initial forming (~4.5 billion yr.) until first preserved rocks (~4 billion years) Why don't we have rocks from Hadean times? Answer: Some rocks formed during that time but were all destroyed by weathering and plate tectonic processes The Early Earth Early Accretion Phase Formation of protoplanets (collisions of planetesimals) Accreting planets would get hot, and partly melt Differentiation of core and mantle began First atmosphere formed (accreted gases, melting, and evaporation of volatiles from impacting objects) Late Accretion Phase Colliding objects became larger Planet size objects hit the Earth Repeated partial melting of the Earth (helped in differentiation of core and mantle) Formation of the moon Loss of the initial atmosphere Slowing of Accretion shown by Moon Craters There were still many impacts at 4.2 billion years ago Impacts from that time obliterated all the older record The rate of impacts dropped to quite low levels by 3.8 billion years ago Since the earth is so close to the moon, it is likely that the same pattern occurred here...
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This note was uploaded on 03/24/2008 for the course GEOS 1014 taught by Professor Sxiao during the Spring '08 term at Virginia Tech.
- Spring '08