Figure 11.6

Geologic time. (A) Earth’s history is divided into eons, which are subdivided into eras, periods, and epochs. We live in the Holocene epoch, nested in the Quaternary period, in the Cenozoic era of the Phanerozoic eon. Note that the Hadean, Archaean, and Proterozoic eons are compressed and not to scale. Collectively they constitute 88% of Earth’s history. The Phanerozoic, greatly elongated here, spans only 12% of Earth’s history. Many of the major biological events of Earth history are labeled here. (B) In this graphic, Earth history is compressed into a single year of time and the four eons are shown. Earth and the solar system form on January 1. Each “month” on the calendar represents about 383 million years. Using this perspective, the immensity of geologic time becomes clearer.