Let's pretend it's the Late Cretaceous, roughly 66 to 100 million years ago. We've got dinosaurs roaming the land and odd-looking early species of birds, although the shark as we know it is already swimming in the prehistoric oceans—which cover 82% of Earth. Redwood trees and other conifers are making their debut, as are roses and flowering plants, and with them come bees, termites and ants. Most of all, it's warm, volcanically active and humid all over the place with nary an ice sheet in sight.