Its a fascinating debate when considered on this small scale, and a slightly futile one on a world scale. What I suspect is that putting aside the possibility of a certain amount of quarrying, and the tiny amount of erosion by us (it seems massive I know, but in the scheme of things its trivial - just compare the changes to the landscape due to slippage as in the whole of the South east side of Mam Tor in the peak district), we can't affect as much as we'd like to think. Sure, we chopped down hundreds and thousands of acres of forest, but it would all grow back in say 500 years if we just left it. This is the blink of an eye in world terms.
I recall a report during the first Gulf war about millions of barrels of oil which the Iraqi's dumped in the Persian Gulf. The environmentalists were wringing their hands and predicting the water being poisoned for 80 years and maybe never recovering fully etc etc. It took less than 15 months for the gulf to clean itself up, with no significant help from us. Of course, it'd be better if it hadn't happened at all.
To nick a line from Crocodile Dundee, we are like fleas arguing about who owns the dog we all live on. I don't suppose its a good idea to deliberately harm our planet on any scale, but I strongly suspect if it gets uninhabitable for us on this world, it will shrug us off and carry on. And I just know the last rock I stood on will still be roughly where it is now in ten thousand years. Humans are arrogant about how important to the world we are, and equally arrogant about how much control we have over nature. I definitely think we should be slow to chop down any more rain forest as we depend on it so much for our well being, but when I hear the cry that man is ruining the environment, I can't help reminding myself that that notion is very much about our vested interest in preserving an environment that we've evolved to prosper in - in other words, we are only ruining the environment in the sense that it may not be healthy for us. In any other perspective, we are merely changing the environment - who knows what else might benefit from global warming for example - maybe tubeworms are cheering, lamas laughing their heads off.
I think I read on this very forum "Don't ever take nature on - you'll lose" (or something close to that anyway). Great topic.
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