This diagram shows the Earth’s history as a vertical strip. At the bottom, the oldest event, the formation of the Earth, is shown at 4600 million years ago. The Phanerozoic Eon of visible life starts at 545 million years ago and extends to the present. The first period of the Phanerozoic eon, the Cambrian Period, extends from 545 million years to 500 million years ago.