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Similarly, in geologic studies, vast quantities of information from widely spaced outcrops have to be integrated.

For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.

The stratigraphic column, a composite of these systems, was pieced together from exposures in different regions by application of the principles…

Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.

Using this established record, geologists have been able to piece together events over the past 635 million years, or about one-eighth of Earth history, during which time useful fossils have been abundant.

The need to correlate over the rest of geologic time, to correlate nonfossiliferous units, and to calibrate the fossil time scale has led to the development of a specialized field that makes use of natural radioactive isotopes in order to calculate absolute isotopes has been improved to the point that for rocks 3 billion years old geologically meaningful errors of less than ±1 million years can be obtained.

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