Colliding Theories

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Science  19 Mar 1999:
Vol. 283, Issue 5409, pp. 1861-1863
DOI: 10.1126/science.283.5409.1861

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When researchers try to find out how the Earth and the moon formed, they quickly come up against the problem that direct evidence is impossible to come by. Halliday and Drake discuss recent progress towards understanding Earth and moon formation using simulations, high pressure experiments and isotope geochemistry. The most widely accepted theory assumes a "Giant Impact" scenario, in which two proto-planets collide and the moon forms out of the debris created by this collision. Many uncertainties remain, such as how large the two bodies were at the time of impact, when the impact occurred, and whether it was accompanied by the formation of deep magma oceans on Earth.