Geologic time divisions.
Each number gives the date in millions of years before present. In the figure, the relative lengths of each time division are not proportional to the absolute time they represent. Solid circles mark the occurrence of mass extinctions (q.v.). Adapted from Harold L. Levin, The Earth Through Time, 7th ed., Fig. 1–15. © 2003 by John Wiley & Sons, Inc. Reprinted with permission of John Wiley & Sons, Inc.