Well, it wasn't extraterrestrially or through evolution. The Late Heavy Bombardment subsided c. 3.85 billion years ago and scientists have evidence of life at 3.84 b.y.a. Interplanetary travel ("astrobiology") is practically impossible, and the very short time interval above, just 10 million years, rules out evolution. Therefore, by far the likeliest explanation is God as Creator.
Xenu’s fault!
