4 November 2009

How Habitable is the Earth?

Posted by Ryan Anderson


Charlie Stross has an interesting post on his blog that asks the question “How habitable is the Earth?” He goes on to conclude, through a great discussion of the evolution of our planet, that the fraction of time that the earth has been habitable to humans is a tiny sliver of the time the Earth has been around, and that furthermore, much of the earth is not habitable for humans because it is water or ice or mountains. If much of our planet, even now, is not habitable, he argues, what hope is there of finding other habitable worlds out there in space?

It’s an interesting discussion, but I find it somewhat misleading. It makes the rather large assumption that for a world to be considered habitable, a human would have to be able to survive for 24 hours, naked, on the surface. Ok, that’s one definition of habitable. But if you are postulating that these humans are capable of interstellar travel, it seems like you might make allowances for the use of clothing and the ability to build shelter. After all, we’ve known about those ones for a while. You could go even further and suggest that these humans might be able to alter the air they breathe, either through individual gas masks, or on a planetary scale. We used CO2 scrubbers on the Apollo missions to make the air breathable, maybe that would work on a planet with otherwise unbreathable air?

I think he’s fundamentally right in terms of human habitability: the likelihood of a planet being perfectly attuned to humans is extremely low. We evolved to live on Earth and nowhere else. We are going to have to make some adjustments to ourselves or our environment to live anywhere else.

The problem is that he then extrapolates and suggests that this might explain the Fermi paradox (aka. if there are so many stars and planets out there, why haven’t we heard from any little green men?). But that is completely off-base! He is essentially saying that, because humans evolved to live on Earth and nowhere else, it is unlikely for anything else to be living out there because there are likely few earth-like places. That does not follow. There could be aliens out there that are completely happy on their planets that would be instantly lethal to us. And it’s entirely possible that if they set foot on Earth they would find it a very hostile and uninhabitable environment (and not just because of the terrified earthlings).

Anyway, it’s an interesting article. Go take a look.

And speaking of interesting articles, have you gone and voted for my MSL: Mars Action Hero article over at scientificblogging? I’m one of the finalists for their science writing competition, so take a look and vote for me if you like it. To see the other entries, click here. Feel free to vote for as many as you like, and remember you can vote daily until the 23rd!