Answer:
a)From the collision of protoplanet and proto-earth
The isotopic homogeneity of this highly refractory element suggests that lunar material was derived from the proto-Earth mantle, an origin that could be explained by efficient impact ejection, by an exchange of material between the Earth’s magma ocean and the proto-lunar disk, or by fission from a rapidly rotating post-impact Earth.
However, it remains uncertain whether more refractory elements, such as titanium, show the same degree of isotope homogeneity as oxygen in the Earth–Moon system.
Scientists still believe the general idea of having an impact forming disk that coalesced into the Moon is probably right, but this paper shows that scientists still don’t fully understand exactly what the mechanisms were. There is a lot of exciting research still to be done in this field!
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