Lunar Origin Theories
The most widely accepted theory about the moon's origin is the Giant Impact hypothesis, where early in Earth's development a Mars sized object(sometimes called 'Theia'), impact earth and from that impact some of Earths substance were thrown up to space and with the substance from the impactor, it coalesced to form the moon.
there are also other theories before such as the fission, capture and co-accretion.
There's also a new one where two moons collided to form one.
see more here:[link][link][link][link][link][link][link]
...and many more out there
see moreplanetary moe comics and drawings here:[link]