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Giant impact hypothesis

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Author Topic: Giant impact hypothesis  (Read 854 times)
Deanna Witmer
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« on: October 18, 2010, 01:21:19 pm »

Difficulties
This lunar origin hypothesis has some difficulties which have yet to be resolved. These difficulties include:
•   The ratios of the Moon's volatile elements are not explained by the giant impact hypothesis. If the giant impact hypothesis is correct, they must be due to some other cause.[17]
•   There is no evidence that the Earth ever had a magma ocean (an implied result of the giant impact hypothesis), and it is likely there exists material which has never been processed by a magma ocean.[17]
•   The iron oxide (FeO) content (13%) of the Moon, which is intermediate between Mars (18%) and the terrestrial mantle (8%), rules out most of the source of the proto-lunar material from the Earth's mantle.[18]
•   If the bulk of the proto-lunar material had come from the impactor, the Moon should be enriched in siderophilic elements, when it is actually deficient in those.[19]
•   The presence of volatiles such as water trapped in lunar basalts is more difficult to explain if the impact caused a catastrophic heating event.[20]
•   The Moon's oxygen isotopic ratios are essentially identical to those of Earth.[3] Oxygen isotopic ratios, which can be measured very precisely, yield a unique and distinct signature for each solar system body.[21] If Theia had been a separate proto-planet, it would probably have had a different oxygen isotopic signature than Earth, as would the ejected mixed material.[4]
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