Recent estimates suggest that the earth was formed at least 4.5 billion
years ago. To visualize the length of geologic time and the relations
between the stratigraphic and absolute time scales, let us imagine a
yardstick as representing the length of time from the origin of the
earth to the present (fig. 19). On one side of the yardstick we plot
time in years; on the other, we plot the divisions of the stratigraphic
time scale according to the most reliable absolute age determinations.
[Illustration: Table 1. The stratigraphic time scale.]