What information do fossil remains reveal?

Fossils reveal that the Earth has a history, and that it wasn't necessarily always like the present day. Dinosaurs lived on Earth for 160 million years (give or take a million or so) and passed away leaving the Earth to the domination of other types of animal, including our distant ancestors. Humans have only been on this Earth for about one quarter of 1 million years, yet by the reckoning of some we run the risk of turning our Earth into an uninhabitable wasteland within the next few hundred years.