This is how the western hemisphere of the Earth may have appeared 90 million years ago during the Late Cretaceous period.. . During this period continental drift, driven by the massive forces of plate tectonics, had broken the supercontinent of Pangea into Laurasia in the north and Gondwana in the south. With a climate much warmer than today's there were no frozen polar caps and the resulting high ocean levels submerged a third of today's landmasses under warm shallow seas creating numerous waterways and island continents.. . In this image much of the incipient North American continent is divided by the Western Interior Seaway, the Isthmus of Panama is submerged by the Proto-Caribbean Sea, and the Pacific Ocean is making an incursion into South America.