Quote:
it is only in the last century that many harmful things have been introduced into the environment.


That's not true at all. As long as their have been animals on the planet, carbon dioxide has been released. Methane gas has been released for a long time. Termites produce more of this than humans produce carbon dioxide.

Millions of years ago, after some big changes, one very harmful, poisonous gas was released into the environment and the planet managed to adapt and survive. The gas??

Oxygen
"The early bird gets the worm, but the second mouse gets the cheese." Steven Wright