the first serious modern scientific explanations of the Moon's origin
was put forward by the aformentioned George Darwin, son of the celebrated
Charles Darwin. George followed in the footsteps of his father by
developing an evolutionary theory of the Moon, more commonly called
the 'fission theory'.
Beginning in 1878, Darwin argued that the Moon could
have split off from proto-Earth when it was still a liquid body,
flung off by Earth's rapid rotation and the action of the Sun's
tides, after which it gradually moved outward over the aeons to
its present position. Darwin's theory, which he arrived at by applying
accepted physical principles about the action of the tides, was
the first scientific speculation about the origin of the Moon that
treated it as a unique event, rather than a commonplace part of
the ongoing process of the formation of celestial bodies within
the Solar System.