GE CLST 70A Lecture Notes - Lecture 16: Geologic Time Scale, Solar Luminosity, Solar Wind
23 Jan 2017
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Document Summary
Geophysical and geochemical constraints suggest formation of the moon via a giant impact, Lecture 16 probably 50-60 myrs after the birth of the solar system. Impact cratering is a ubiquitous process affecting planetary surfaces. Cratering rates were very high in the beginning, then rail off. The mares of the moon formed between 3-4 byrs ago. Lunar cataclysm due to instabilities in the outer solar system, 3. 8-3. 9 byrs ago. Hadean earth: massive volcanos, very hot, magma ocean, constantly pummeled by impacts. However, it cooled relatively quickly and water began to condense. Tiny pieces of zircon from hadean earth (4-4. 4 byrs old) can be found in western australia. High o-18 values suggest clay-rich protoliths were melted to form the magmas that crystallized. Some hadean zircons have included minerals that incorporate water in their structure into the zircons - clay requires low temp hydrosphere-crust interactions. Thus, the rock record suggests earth had an ocean by ~4. 2 byrs.
