Dating relative rock
Nicolas Steno, William Smith, Georges Cuvier, Alexandre Brongniart, and James Hutton developed the basic rules for the science of stratigraphy.
Absolute age-dating tells how long ago an event occurred.
Using these methods, geologists have created a geologic time scale for organizing past times in earth’s history.
Presumably if all the world’s outcrops were integrated, sediments representing all of geologic time would be available for examination.
This optimistic hope, however, must be tempered by the realization that much of the record—older than 541 million years—is missing.
Furthermore, useful fossils are either rare or totally absent in rocks from Precambrian time, which constitutes more than 87 percent of Earth history.