I'm gung-ho on colonizing Mars. Let's do this!! It would be an amazing adventure and a useful scientific endeavor. But there's something I really want us all to keep in mind as we do it. Colonizing - even terraforming - is not an "insurance policy."
It's tempting to think in terms of eggs and baskets. Earth is one big basket, and Mars is another, and the more baskets we can distribute our eggs to, the better our chances of survival - as a species - if one of those baskets breaks.
But on closer inspection, that metaphor just doesn't work, because Earth is not just any old basket. If we drop it, we are straight-up doomed. Fixing our problems on this planet is way, way, WAAAAYY more important than any terraforming effort of some other planet.
For the foreseeable future, any planet we terraform is guaranteed to be:
- way too hot or too cold,
- too dry,
- much more difficult to mine for resources,
- far away from assistance,
- devoid of supporting life
That last item is the most pressing. To take one example, planet Earth has a nice coating of soil on it. Soil is astonishingly complicated. 94 percent of all the Earth's bacteria are in the soil subsurface. A teaspoon of farm soil contains tens of yards of fungi, and the same amount from a coniferous forest can hold tens of miles. Custom mixtures have evolved for custom environments all over the planet. And here, it is literally cheap as dirt. Nothing like it exists anywhere else in the solar system and if you placed it anywhere else in the solar system it would immediately die.
No soil, no food.
That makes Earth pretty freakin' essential, I'd say. We mess things up here, it is game over, man. Game over! There is no insurance policy big enough that covers it. Could we terraform Mars? I think so, yes. But if we can't keep the Earth intact at the same time, what's the point? This planet has been human habitable for a hundred million years at least, and that's just my own conservative estimate as a non-expert. Unlike anywhere else, it can remain so for another hundred million years, without our intervention. In fact, it's our intervention that is the only real threat! That's some harsh irony.
A hundred million years is an absurdly long span of time - longer than any of us can imagine, and time enough to accomplish amazing things - but we have to earn it, by self-organizing, by setting our priorities, and by figuring out how to curb our worst behaviors. As a bonus, if we can last long enough, we're bound to make contact with other intelligent life in the universe, via robotic probes or otherwise. In fact, living sustainably may be the cost of admission to a galactic community. Suppose we discover life in a distant solar system, and show up with the terraforming equivalent of dumptrucks and dynamite, and claim that we need a spare planet because we've screwed up our own beyond repair? For the sake of all other intelligent life everywhere, It would be a righteous act for those aliens to nuke us out of orbit, follow us home, and post guards all around the Earth to keep us contained until we sort ourselves out.
That's some of what's in play here: We are expansionistic apes with extremely short attention spans keen to build an incredibly frail and suspiciously symbolic outpost, because we believe deep within ourselves that our whole planet of origin could go up in smoke any moment - not from any external threat, which geologic history has shown to be very remote - but from our own careless nature. Or maybe just the careless nature of those other apes -- the ones with the different religion, or the suspiciously different fashion sense.
We evolved as nomadic wanderers, relying on other life to reset our damage after moving on to the next fresh area. Our self-organization has helped us move beyond that, but we need to leave it entirely behind, if we are going to earn our deep time on this planet.
An outpost, a colony, a terraforming effort - these are experiments, adventures, proving grounds. But they are not an insurance policy. Not a backup plan. We lose Earth, we lose it all.