[bellaire]

>> It can kill itself on a whim, and has come close to doing so in the geological past.

I'm not sure what you mean by "close to" killing itself. In the geologic past, life itself has survived rapid toxic oxygenation, the complete freeze-over of the planet's surface, and the complete sterilization of surface life including boiling off the world's oceans. Microbial life still survived that last one in insulated rock miles below the surface. What catastrophe are you proposing we could induce that would do worse?

>> In the long run, nature is a chaotic, not a homeostatic system, and "balance with nature" is an oxymoron.

Now I invite you to read my comment again.

[zeteo]

I've invited you to read my comment again because I felt you were mis-representing my point. Regarding the rest,

http://en.wikipedia.org/wiki/Survivor_bias

http://en.wikipedia.org/wiki/Life_on_mars#Liquid_water

Considering that there have been very severe extinction events in the past; that the best evidence we have for Mars indicates it sustained life in the past, and then lost it; it is special pleading to argue that life on Earth, or at least multi-cellular life, has some hypothetical property that will make it go on forever. On the contrary, the multitude of documented dangers, the suddenness and magnitude of shifts in the paleobiological record indicate that life on Earth may yet go completely extinct within a relatively short geological time span, even were all humans to commit suicide today.

[bellaire]

I see what you are saying, but I don't agree. You are reversing the evidence in your assertions. There is no evidence that life has existed in the past on Mars. If there were, that would be fantastic, and many people believe such evidence will be forthcoming, but as of right now, there is none that is accepted in the mainstream.

As to your other point, the very fact that life on Earth has come close to extinction, and yet survived, so very many times indicates that there is an empirical (not theoretical) basis for my claim that life (in some form) tends to bounce back. The mechanism is the fact that bacterial and archael life forms live deep within insulated areas of Earth's crust and retain relatively (geologically speaking) modern genes for traits such as aerobic respiration. Survivorship bias does not imply that in some situations there are no survivors, that is a misapplication of the idea.

Now, it's certainly possible that life could be extinguished in a short geologic time span, that I don't refute. And of course, in around a billion years the sun's total radiative output will make life all but impossible on Earth's surface. But in the mean time, evidence suggests life is incredibly hardy.

I suspect, anyway, that we are talking at cross-purposes. The topic was sustainability vis a vis human activity. You rightly point out that we are not in total control, that things can go awry without our intervention. Nature is indeed a chaotic system. However, I suspect you do not disagree that we can choose to avoid certain paths that would inevitably lead to our own destruction. We probably can't avoid all of them, as we are not omniscient, but my main point is that it behooves us to think about it, and to attempt to act responsibly, not in a sense of maintaining the natural state of the world as a static equilibrium, but merely to survive as best we understand how.