Well, very early in the earth's history there was water. Lots and lots of rain fell at one point (for several years running, or so the theory goes). There's also the possibility that the earth was smacked into by another planet, and from that came the moon and a very different earth; e. g. that the collision precipitated the rise of land above sea level. See http://home.earthlink.net/~yvonr/library/margin/moon.html
for a pretty good summary.
Another theory is that life originated elsewhere, or that the building blocks did, and was brought here via comets and/or meteorites. See http://www.planetary.org/html/news/articlearchive/headlines/2001/cometlife.html
for some info on this theory.
One reason why it will be tough to really know these things for sure is that early evolution didn't leave much in the way of fossils, because individual cells don't have anything which is hard enough to imprint as a fossil. So we rely on chemistry, and DNA, and conjecture quite a bit.
Plus, there was an experiment in 1953 by Stanley Miller and Harold Urey. They used a sterile, enclosed system consisting of a flask over a heat source, a spark chamber, and various other tubing They added sterile H2O, H2, CH4, and NH3 to the sealed system. Heat was applied under the flask to simulate volcanic action, and this was enough to turn a significant portion of the water into steam. A spark chamber periodically discharged electricity into the gasses to simulate lightening. See:
In any event, the experiment showed that amino acids (the building blocks of proteins) could arise from these conditions. And don't forget, the earth had about a billion years for this to happen before we start to see rudimentary evidence of life - which was life that was clearly more complex than how life originally was.