Not much is known about how the moon came about, interested parties are therefore reduced to looking for clues and formulating theories throughout the years. The earlier versions were based on guesswork and how such relations were thought to be formed in general, whilst later ones had a bit more solid evidence and information to go on and are thus, believed to be closer to the truth. To give away a part of the story, some theories turned out to be better than others if one knew what the observations and evidence we now have are. These were largely due to the examination of rocks brought back by the Apollo missions.
Here are some of the observations:-
(I) the ages of rocks on the Moon were very slightly older than those found on the Earth.
(II) The composition of Moon rocks was very similar to that of the Earth’s mantle.
(III) Both have exactly the same ratio of certain oxygen isotopes whereas rocks from Mars and meteorites do not.
(IV) The Moon, compared to the Earth, is poor in elements that melt at low temperatures (volatile elements), nickel and cobalt that are found in iron-bearing elements and has a much smaller iron core.
(IV) Lunar basalt has ten times more titanium (remains solid at high temperatures) than basalts on Earth.
(V) The Earth`s density is much higher than the Moon`s (5.515g/cm3 to 3.34g/cm3).
Next (THE FISSION HYPOTHESIS)