The fossil record of the Adapiformes is quite considerable. The fossils are first found in the earliest Eocene, 55 million years ago (mya). They lived in four continents (North America, Africa, Europe and Asia). The Eocene was a period when the Earth was much warmer than today, with very extensive tropical forests, far more so than today. The widespread remains mean a much earlier origin, and molecular clock dates suggest that primates evolved more than 80–90 mya, nearly 40 million years before they appear in the fossil record.