Fire has been a major force in the evolution of land-based life. Even more so in the distant past. In the Cretaceous (70 - 140 million years ago) both tempera

Fire has been a major force in the evolution of land-based life. Even more so in the distant past. In the Cretaceous (70 - 140 million years ago) both temperatures and the oxygen ratio in the atmosphere appear to have been higher than now. The whole planet was covered in a thick tropical forest -- and it burned easily. The dinosaurs had to contend with continent-wide forest fires, and their bones are often found in the middle of a layer of charcoal.