[gus_massa]

Sadly the current most popular hypothesis in the scientific community is the collision of a smaller version of the Earth with another planet https://en.wikipedia.org/wiki/Origin_of_the_Moon

[NikkiA]

Oddly enough, that article doesn't mention the name 'Theia' or even link to the larger page on the collision theory that searching for 'Theia' brings...

https://en.wikipedia.org/wiki/Theia_(planet)