Gravity is a Scientific Theory. (If you don't know the Difference between a 'Theory' and Scientific Theory, Use google)
That is true, but we are speeding the process up, Either way Its bad for Us (Humans). Yeah, Sure It could be Ok for earth Itself and we don't know that as Right now we care about keeping ourselfs alive, we are 'programmed' that way.
Ice age... But the Giant hugeass Comet (Meteoroid, Asteroid, I get them all mixed up) hit earth and did the opposite of an Ice Age, the Ice Age occurred later due to the Toxic clouds (Again, Not in the mood to find the exact chemicals and terms) blocking off the Sun's light, that was due to to the Volcanoes (Yes, volcanoes were also going off a while before the Comet) and the Comet hitting, and causing everything to cool down; The dinosaurs were all dead by then.