Though it sounds like the plot from recent scifi movie Prometheus, it's an old idea that even the celebrated nineteenth century physicist Lord Kelvin and Nobel winning geneticist Francis Crick have advocated. That's right — the evolution of life might have its beginnings on another planet.

Over 120 years ago, Kelvin shocked the British scientific community in a speech about what he called "panspermia," where he suggested that life might have come from planets smashing into each other and sending bits of life hurtling through space. He and a few colleagues had hit upon this notion after observing the massive 1880 eruption of a volcano on Krakatoa. To be more precise, they observed the aftermath of the volcano, which completely sterilized the island. No life was left at all. But then, within months, seedlings began to sprout and life took hold again.

Where had that life come from? To naturalists of the nineteenth century, it was obvious that it had drifted there from nearby islands. Seeds and insects blown on the wind, or floating on the tides, had begun the process of re-greening the stricken landscape. This got Kelvin thinking about the origin of life on Earth. Couldn't the same thing happen to barren planets drifting in space? Perhaps life had drifted to Earth on the stellar winds.



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Image: Probes landing, NASA