Back home, the Mesozoic era ended with a comet slamming on Mexico's Yucatan Peninsula. In this scenario, what killed off the dinosaurs wasn't a space bomb, but two series of volcanic eruptions, one from Siberia and one from Antarctica. Each one released enough lava to fill in all 50 United States a mile deep. With that in mind, what would 65 million years of environmental change accomplish? How different would the topographies of Siberia and Antarctica be today?