It's called astrobiology: the idea that life emerged somewhere in the cold reaches of space, and only made it to Earth belatedly, after stowing away on a meteorite or comet. It sounds far-fetched, but astronomers have a growing body of evidence that supports the idea. They added another piece this week, in the journal Earth and Planetary Science Letters.***
And after all, say the astrobiologists, life had to originate somewhere. Reassuringly, their leading proposals involve scenarios considerably more humble than standard Hollywood images of luminous humanoids arriving in gleaming steel cylinders.
In this week's finding, scientists isolated from an Australian meteorite two molecules called uracil and xanthine, each of which consists of 12-15 atoms of carbon, oxygen, nitrogen, and hydrogen. (The carbon in the samples differed in makeup from what's found on Earth, indicating the find wasn't the result of contamination once the meteorite landed.)
The find suggests that somewhere out in space conditions are right for such complicated molecules to form spontaneously. Even more exciting, uracil and xanthine are precursors of two pivotal molecules in living organisms, RNA and DNA. The way astrobiologists interpret this, life may not have zapped into existence in a single, unique flash in some earthbound primordial soup after all (which was the way I learned it in school).
Rather, the building blocks may form, en masse, in cold interstellar factories, and then perhaps travel the cosmos on the backs of comets, waiting for a crash landing. Like little starter kits.