man does effect the environment with pollution and in turn would destroy plant life and other living beings. however it is not necessarily a permanent 'earth changing situation' rather than what would be man's own self destruction. The planet would rebound, it has before, would again. Just because man may destroy himself by pollution does not mean the planet completely comes to an end or would stay in that condition always.. the planet would just readjust itself minus mankind..sort of like what happened with the dinosaurs. something else would take over..
chickens are a direct link to the dinosaurs, maybe they would take over and then evolve back into dinosaurs (because man cant fry them up anymore for the reason mankind going extinct) that is of course the chickens dont all get taken out because of the pollution.
probably the planet would just start over from scratch until the day the sun expands past the orbit of Mars when it turns into a giant dwarf eventually collapsing in on itself after taking out the inner planets in a few billion years?
but there are other cycles the planet goes through in its journey along with the rest of the solar system that does play an effect due to events in space.
The problem for Earth would be if the electromagnetic field or whatever it is that deflects the Sun's full dose of radiation disappeared.., if that happened it over forever for life as we know it. Probably what did Mars in.
