Opinion: How habitable is the earth?

After the slow-burning evolution of hominins in Africa, our ancestral populations erupted out into Eurasia in a geological eye-blink, spread into the Americas by way of the Bering land bridge (sea levels being somewhat lower during the ice ages) and finally reaching even the remotest islands of oceania around twelve thousand years ago.

Today we're ubiquitous. Even our pre-industrial ancestral cultures...occupied a slew of geographical environments that put cockroaches to shame.

So you'd think that, to a first approximation, the Earth is inhabitable by human beings. And this tends to colour our approach the prospects of finding extrasolar planets that might be hospitable to human life.

"Actually," says Charles Stross, "I think this is not quite the case. In fact, to a first approximation, from the perspective of prospective interstellar colonists, the Earth is uninhabitable."

That we could imagine otherwise bespeaks a profound cognitive bias on our part (and a degree of relativism: because when all's said and done, the Earth is a lot less hostile than, say, the surface of Venus or the cloud base of Jupiter).

Why is the Earth uninhabitable? To find out, read the entire column.