Welcome to Prehistoric Answers. What would you like to know?

This is a hotly debated topic, and even has its own name: abiogenesis. One widespread thought is that RNA, not DNA, was the first building block of life. The replication of this RNA-based life required multiple resources which resulted in competition and natural selection among lifeforms. Then DNA arose and formed proto-cells. How exactly life arose in the first place is still at least partially uncertain.

But no, aliens are probably not the answer. :) Styracosaurus Rider (Speak to the Rider, your Lord and Master) {Look upon my servants} 15:55, November 13, 2011 (UTC)