[rimantas]

This answer is exactly the reason I asked what does it mean. Serious question: why keeping polar bear alive makes planet sustainable? Who kept dinosaurs alive? Or any other species which went extinct before we even were there? I think we vastly overestimate our influence on the earth (just compare total mass of humans to that of bacteria, not to mention plants) and our responsibility for it.

If human brings some alien seeds and the new plant starts to dominate the "locals" we see that human as criminal. Would winter or water do the same it's natural then. We are not the children of nature. We are the part of nature, and the small one. Sure, we have an ability to reflect on our actions and inflict disproportional changes to environment, but still.

Just for some context. Fukushima nuclear disaster: nobody killed, 39 injured. Japan earthquake and tsunami: more than 15 000 killed, more than 5000 injured, more than 7000 missing. The sentiment is still "get rid of nuclear, save the planet". Who is killing whom? Indian Ocean tsunami? Haiti earthquake?

George got it right: no matter what we do planet is here to stay, it is not going anywhere. We cannot in any way affect the sustainability of it. Only of our own lives.

[gnosis]

"no matter what we do planet is here to stay, it is not going anywhere. We cannot in any way affect the sustainability of it"

The earth is undergoing one of the largest mass extinctions in its entire history. And it's largely humans' fault.

The eath is undergoing massive climate change. And it's largely humans' fault.

Humans are polluting their environment on an unprecedented scale. We are causing enormous losses in biodiversity. And this does not even begin to address the devastation that a large-scale nuclear war would cause -- something that's still a very real possibility.

Sure, Earth's geology will survive, as its surface is like the rind on an apple and it doesn't matter much to the Earth's interior what happens on the surface.. and we can barely affect the geology of the surface.

But we can and certainly do affect life on Earth. Sure, humans might have a hard time killing off all life, but we're doing a pretty good job killing off a good fraction of it. And yes, humans are a part of nature, but a particularly destructive part.