How Earth was able to produce life step by step

And which other worlds could have done the same. Looks like answers are emerging.

Artist’s impression of Earth in Archean Eon, 4 to 2.5 billion years ago, by Tim Bertelink. Via Wikimedia Commons

How could life emerge on a previously lifeless planet? Is life’s origin a chance event, or a stepwise process? Is it likely that worlds other than Earth have also come up with life; and if so, which ones?