How long have we got? Depending on who you ask, we’re roughly halfway through the time of tolerable tenure for life on Earth. The planet has been around for 4.6 billion years, give or take, and it’s got about that much more time before the swelling Sun boils our bathwater.
Relatively speaking, it didn’t take very long for life to appear once the Earth had cooled down enough to support plenty of water. But notice that it took a surprisingly long time, something like 2.5 billion years (as indicated by the red bracket), before the first eukaryotic organisms came along. That’s a sizable fraction of the entire lifespan of the planet! Something extraordinary and improbable must have happened, something very lucky for us, since those little bugs were our ancestors. One way to put this in perspective is to say that, if life suddenly vanished from Earth right now, it’s reasonable to assume there would be enough time for it to develop again before the Earth was sterilized by the Sun. But it is much less likely that there would be enough time to get from simple bacteria to eukaryotic life again. On the plus side, if we simply kill off all the people, or even most of the vertebrates, there should be plenty of time to regroup and try a few more times and making something intelligent.
The latest issue of Technology Review magazine has a provocative essay by Nick Bostrom along these lines. Entitled Where Are They?, it touches on Fermi’s paradox regarding extraterrestrial life. Namely: if life in the universe is commonplace, then why aren’t we seeing any evidence of it? His conclusion is that some catastrophic event, call it the Great Filter, is blocking life on other planets from reaching the point where it can contact us. If you follow his reasoning this far, then you have to ask if the Great Filter is behind us or after us. Was, for example, the rise of eukaryotic complexity so singular, that we are the only planet in the entire galaxy to pull it off? On the other hand, what if the Great Filter is ahead of us? We, and every other planet like us, may well destroy ourselves with near certainty, either through suicidal violence or self-poisoning waste. Fossil fuel has given us wealth and a means of ascent into orbit, but we may well squander it and kick away the ladder.
It’s hard to argue with Bostrom’s reasoning. One thing that’s still not very clear to me: how likely is it that Earth-like civilizations in our galaxy would be able to hear our “leaking” radio frequency transmission? That is, not the messages we send intentionally, but just the noise we generate on a typical day. This seems to bear directly on this problem. Not much time has passed for other civilizations to hear us, but if they could hear us, then shouldn’t we be able to hear them? If we should be able to hear other civilizations as advanced as our own, but instead hear nothing, that seems pretty clear evidence that the Great Filter is behind us and not ahead of us. At any rate, I recommend you read the whole piece, if only to follow his rationale for the following comment:
If [on Mars] we discovered traces of some simple, extinct life-form–some bacteria, some algae–it would be bad news. If we found fossils of something more advanced, perhaps something that looked like the remnants of a trilobite or even the skeleton of a small mammal, it would be very bad news. The more complex the life-form we found, the more depressing the news would be. I would find it interesting, certainly–but a bad omen for the future of the human race.
By the way, Tim O’Reilly has a good piece about this same topic over at the O’Reilly Radar blog: Fermi’s Paradox and the End of Cheap Oil.