Panspermia, the idea that life on earth may have been accidentally seeded here from somewhere else in the cosmos, is a convenient rescue strategy for materialist explanations of life's origins. The well known problem with the approach is obvious: it only pushes off the enigma of how the originating, colonizing life itself originated. A Scientific American column by Columbia University astrobiologist Caleb A. Scharf suggests another problem with panspermia that I hadn't thought of.
In two words, it's natural selection. You could imagine extraterrestrials as purposefully dropping that first specimen of sulphur-eating bacteria (or whatever) here with high hopes of its developing into you and me three and half billion year later. (That was the premise of this summer's interesting Ridley Scott science fiction movie Prometheus, with its nod to intelligent design.) Barring the involvement of super-intelligent ETs, the most likely scenario being discussed is that life came here on a comet or an asteroid.
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