Giant impact hypothesis The giant impact hypothesis is that the
Moon was created out of the debris from a collision between the
young Earth and a Mars-sized protoplanet. This is the favoured
scientific hypothesis for the formation of the Moon. Evidence
for this hypothesis comes from Moon samples which show that: -
the surface of the Moon was once molten - the Moon's apparently
relatively small iron core and a lower density than the Earth,
and - evidence of similar collisions in other star systems
(which result in 'debris disks') There are several unanswered
issues with this hypothesis. Lunar oxygen isotopic ratios are
essentially identical to Earth, with no evidence of a
contribution from another solar body. Also, lunar samples do not
have expected ratios of volatile elements, iron oxide, or
siderophilic elements (chemical elements which bond with iron),
and there is no evidence that the Earth ever had the magma ocean
implied by the hypothesis. The Earth's relatively large natural
satellite, the Moon, is uniq