bolid impact question

Reply Thu 27 Jun, 2013 07:13 pm
It is said that moon was formed when a bolid impacted the earth, a chunk of the earth was blown away and turned into a moon. I don't know the exact sequence of events that circumvent this theory. But my question is, doesn't it mean that almost all of the quartz of the earth should be shocked?. And of course, that of the moon, too?. If the moon was part of the earth, it should have water as the earth has it, but the moon hasn't it. Even still I can not cope with the idea that such impact created a rounded planet and a rounded satellite at a perfect distance, one from each other, as to let life to succeed. One would expect that impact like that would create shapeless celestial bodies with increasing motion gained through the impact and the gravity of other bodies when passing near them. I can not stand on this theory, it is quite dubious, I don't know how it is broadly accepted.
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Reply Thu 27 Jun, 2013 07:20 pm
a reasonable question. The earth is a quite dynamic system and all the quartz or silica minerals have been subducted, moved, subject to mountain building re-melting (anatexis) and plate movement. The hypothesis that the moon WAS an ejecta body did use some evidence of some shocked quartz from the Canadian and Russian Shields.
The ejecta that resulted in a lunar body also occurred at a time that much of the earths crust and upper mantle were still plastic and almost molten. But you can investigate Post-Hadean Shocked quartz on the web and red some papers on the subject
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Reply Thu 27 Jun, 2013 07:37 pm
I agree with Farmerman. The main thing to remember is that the impact that formed the moon occurred at a time when the Earth was still very molten, and the impact itself released so much energy that both bodies (moon and earth) were liquified to a certain degree. A portion of the Earth's mantle (and a portion of the impactor) may have remained intact, but the bulk of the material that formed the moon was probably completely liquified and then accumulated solid chunks of ejecta that were in its orbit.

By the way, the moon does have water on it (in the form of subsurface ice), but I think that's more because of accumulation of cometary debris than it is a remnant of original water.
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Reply Thu 27 Jun, 2013 07:46 pm

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