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It came from outer space鈥� (Image: Stocktrek Images/Getty)

HOW did life begin? Charles Darwin speculated that it happened in 鈥渟ome warm little pond鈥�. Since then, many other possible crucibles have been identified: deep underground, in the open ocean, by hydrothermal vents on the ocean floor, on a radioactive beach and on the surface of a lump of clay. The hypotheses have little in common except for one thing: they take it for granted that Earth鈥檚 life must have arisen at home.

What if it didn鈥檛? In the early 1970s, astronomers discovered that space was full of complex organic molecules, some of them forming part of the comets and meteorites that occasionally crash-land on Earth. Life also seems to have arisen here with improbable haste. Almost as soon as it was habitable, Earth became inhabited. Could the transition from prebiotic to biotic chemistry really have happened so fast?

The observations reignited an alternative account of how life began, first proposed in 1871. Panspermia holds that life got going somewhere else 鈥� perhaps on Mars, perhaps further afield 鈥� and was carried to Earth on a comet or meteorite.

The idea remains an unproven hypothesis on the fringes of mainstream science. But the tide is turning, according to Chandra Wickramasinghe of the University of Buckingham, UK, one of the scientists who revived panspermia in the 1970s, along with Fred Hoyle. 鈥淭his was conjecture in the past, purely theoretical, but now we have evidence for it,鈥� he says (see box). 鈥淚t鈥檚 changing, slowly but surely.鈥�

According to Wickramasinghe, the galaxy is teeming with life, and our biosphere is just part of a vast, interconnected cosmic ecosystem. Genetic material and even living organisms are constantly exchanged between Earth and neighbouring star systems. Evolutionary change is largely driven by novel genetic material arriving from space, most likely in the form of viruses.

Others are a little less ambitious, arguing merely that life first evolved on Mars. 鈥淚 think the case for Mars as the origin of Earth life is pretty good,鈥� says Peter Ward, a biologist at the University of Washington in Seattle.

Nonetheless, confirming that our distant ancestors were extraterrestrials would have a profound effect. 鈥淚t would mean a re-evaluation of biological dogma,鈥� says Wickramasinghe. 鈥淒arwinian evolution is not a closed box. We have to regard evolution on our planet as the expression of something that has taken place over a vast region of space.鈥�

鈥淐onfirming that our distant ancestors were extraterrestrials would have a profound effect鈥�

Socially, the biggest effect would probably be on religion. 鈥淚t鈥檚 a big blow,鈥� says Ward. 鈥淔or some religious fundamentalists, it is an axiom that there is but one life and it is here on Earth.鈥� Wickramasinghe agrees that religions will be troubled, but not for long. 鈥淢y guess is that leaders would be able to incorporate it into their existing theology 鈥� they鈥檝e always been remarkably adaptable in taking on new developments.鈥�

Wider society would follow suit 鈥� and the effects could be positive. 鈥淯ndoubtedly there would be resistance and denial,鈥� says Wickramasinghe. 鈥淗umans are very conservative. But ultimately, we鈥檇 come to think of ourselves not as terrestrial creatures, but as creatures of the cosmos. And the sympathy that we now feel for things that are happening across the planet would extend on a cosmic scale.鈥�

Read more: 鈥�10 discoveries that would change everything鈥�