Guess the dinosaurs didnt make it in time and God tossed a rock that way . well you get the idea...

Only Mars is a candidate for terraforming, and it won't work too well there. Not enough gravity to hold in a decent atmosphere. There's also the problem that any group of humanity living on another planet will never be able to return home, unless that planet had the same, or almost the same, gravity. In effect, planetary colonization will create a sort of penal system. You can go, but you can't come back.

Well, sure you can come back, its just going to take alot of physical conditioning. I suppose that sitting on a rotating space station for a few years could do it, just slowly increase the speed of the spin so that your body gradually adapts to the rigors of a heavier gravitational field. Inversly, when you go back, you would probably be the strongest person on your block :)

Also, learning how to terraform by looking at history is a bad way to terraform unless you dont want to be able to live there for about a billion years...