During the rise of mammals, Earth’s temperatures spiked in a scary way that the planet may experience again soon.
They were strange days at the beginning of the age of mammals. The planet was still hungover from the astonishing disappearance of its marquee superstars, the dinosaurs. Earth’s newest crater was still a smoldering system of hydrothermal vents, roiling under the Gulf of Mexico. In the wake of Armageddon our shell-shocked ancestors meekly negotiated new roles on a planet they inherited quite by accident. Before long, life settled into new rhythms: Earth hosted 50-foot-long boas sliding through steam-bath jungles, birds grew gigantic in imitation of their dearly departed cousins, and mildly modern mammals we might squint to recognize appeared. Within a few million years, loosed from under the iron heel of the vanished giants, they began to experiment. Early whales pranced across a Pakistani archipelago on all fours, testing out life in the water. The first lemur-like primates leapt from the treetops, and hoofed things of all varieties dashed through the forest.