Question: How was the Earth created, and do we know why? Surely millions of years ago when there wasnt any humans there was some sort of 'alien' cells were left here and thats how we were made. So in theory, aren't we all some sort of 'alien'?

Katherine Haxton answered on 10 Mar 2012:

Scientists have theories about how the earth was formed. Most theories say the solar system was formed by the dust and rubble of older stars that exploded, that then came together and made the sun and the other planets. Stars make the elements that we’re all made of, things like carbon, oxygen and nitrogen. Studying the geology of the earth tells us more about what the early planet was like.
There are lots of theories about how life originated on earth and some scientists think that key chemicals or perhaps cells might have come from space.
Some chemists work on this and try to find combinations of chemicals that can self-replicate (form things like themselves) in conditions similar to those we think existed on the early earth. Then those systems would have to evolve over a few billion years into simple cells and then a few billion years later into us.

If ‘alien’ cells were left here, where and how were the alien cells formed? I’m not sure if we’re some sort of alien, but I do know that we’re made of the stuff of stars.