Abiogenesis -- when did life first appear on the earth?

I should have probably included the link to the wikipedia article. The two links provided (thus far) really haven't advanced the information provided by wikipedia, but I still appreciate them.

http://en.wikipedia.org/wiki/Abiogenesis

I should probably add the reason that I'm doing this bit of searching: I'm in the process of writing some science fiction stories and need this information for background material (that may not appear in the novel). I don't like to work off guesswork.

On the third references given - this suggests that stromatolites appeared approximately 3.5 billion years ago. I do not see this saying that this represents the beginning of life on earth as we know it, but it does qualify as a response to my question. I would like to see something that could be tied via evolution to life as we know it today.

As to wiki's accuracy, that is an arguable point, as the cell created by the Penn State folks is artificial, not life bearing, or something that can continue living by reproduction. Hence, it is not life as we would define it. Nice try (on the part of the researchers), though, and certainly useful for its purpose.

Questioning Everything - I'll take the speculation, especially if you have something to base it on. I could go with the traces left in strata of soft-celled creatures, but I'm just a bit too rusty (and old) to consider it credible.

And yeah, I know that this isn't going to be useful to convince creationists that believe the earth is only 6,000 (or so) years old that they're shooting in the dark.

It is just that I felt that since this forum is one of the most widely read, I'd get some of the better responses.

zaatheist -- I'll take links as well as good bibliographical references (that I can use to look up the books on Amazon--actual links to the Amazon listings are even better).

For those interested, here's the link to the Florida research (provided in response to another question): http://www.msnbc.msn.com/id/29430688/

For those who don't want to look up the Florida reference and read it: "AEGIS is not self-sustaining, at least not yet, and with 12 DNA building blocks — as opposed to the usual four — there's little chance it will be confused with natural life." So, the wikipedia article still stands, but we are definitely getting closer. Whether it will provide evidence of abiogenesis as imagined and theorized by science is open to question. It may demand new theories.

As one respondent pointed out, this whole area of science is in its infancy. Now, I have to take what we have and project it forward several hundred years and hope that I haven't guessed wrong (always a problem in writing science fiction).

I give thumbs up for responses that address the question (I don't give thumbs down) and will select a best answer sometime later today. Many thanks for the responses (and those who have yet to respond).