When did life first appear on earth and what is the evidence for this?

Question

When did life first appear on earth and what is the evidence for this?

Answer 1

The Bible, in the Book of Genesis.

Answer 2

I would assume that by "life" you mean life in general and not human life.

Then in that case it is in the Middle Proterozoic Era that the "first appearance of sexually reproducing organisms. Which is around...1000-2000 million years ago. Since it seems to be in between, I would assume that it is 1500 million years ago.

Answer 3

The oldest signs I've heard of are carbon deposits in Greenland that are presumably biological in origin, and they date to around 3.7 billion years.  I seem to remember alge-like things turning up as body fossils from around 3 billion years, but I can't think of a source for those.