At about the time our ancestors appeared, the Earth was seized by a geological convulsion: our roots lie in a bombardment episode. Forty-two million years ago, intense volcanic activity spread throughout the whole Pacific area, from Japan to the Peruvian Andes, in New Zealand and the island arcs and trenches of the Philippines. The sea floor itself, from the Indian Ocean to far northern latitudes, was profoundly disturbed, the floor of the Indian Ocean, for example, beginning to spread rapidly out from a central volcanic ridge. Nor was this great disturbance confined to the Pacific Ocean. In Africa, there was a sudden uplifting of land in Kenya. The same happened to the western side of North America. And it was a time of intense mountain building which saw, for example, the rise of the Pyrenees in Europe.
Coincident with these great upheavals was a dramatic cooling of the Earth, in the form of a series of rapid and sharp temperature drops. The oceans became cold both at the surface and in deep waters. This was reflected in an accelerated extinction of many important categories of plankton, the extinctions happening in a step-like manner matching the temperature drops. On land, although many parts of the globe remained warm in summer, winters in equatorial regions developed a Siberian harshness. By the time this period had grown to a close, a few million years later, the mammal population had crashed and the forests of the Earth had shrunk: palm trees had vanished from Greenland, and the jungle from England.