“An extrapolation of the genetic complexity of organisms to earlier times suggests that life began before the Earth was formed. Life may have started from systems with single heritable elements that are functionally equivalent to a nucleotide.” -Alexei A. Sharov & Richard Gordon
We talk about the origin of life on Earth with bated breath, wondering all the time how things occurred to make our planet unique. But within that big question lies an assumption that may not be true: that life on Earth originated on Earth itself. It’s entirely possible, based on what we’ve seen out there in the Universe, that life didn’t originate here at all. Rather, it could have come from a primitive, pre-existing world, or even from the depths of interstellar space itself.
If it’s the latter case — interstellar space — then perhaps we don’t even require a planet at all to create the more primitive forms of life itself. Perhaps all you need is a molecule that encodes information, reproduces itself, and converts external energy for use in biological processes. And if that’s the case, the origin of life may bear very little resemblance to what life has evolved into today.