USGS on-line publication about the relative and radiometric geologic time scales, age of the earth, index fossils, and related topics.

Describes this method, used primarily to date marine sediments, and provides access to the global seawater strontium curve and a user-friendly table for converting 87Sr/86Sr values to numerical ages.

Chart correlates geologic, paleontologic, and absolute time scales, also including glaciations.

Geologic time scale with links for each time interval.