Dating Standards
GSSAs are defined by the International Commission on Stratigraphy and are used primarily for time dating rock layers older than 630 million years ago (mya), before a good fossil record exists. The record becomes spotty at about 542 mya, and the ICS may well have resort to defining additional GSSA's between the two dates.
For more recent periods, a Global Boundary Stratotype Section and Point (GSSP), largely based on research progress in geobiology and improved methods of fossil dating is used to define such boundaries. In contrast to GSSAs, GSSPs are based on important events and transitions within a particular stratigraphic section. In older sections, there is insufficient fossil record or well preserved sections to identify the key events necessary for a GSSP so GSSAs are defined based on fixed dates.
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Famous quotes containing the words dating and/or standards:
“We go on dating from Cold Fridays and Great Snows; but a little colder Friday, or greater snow would put a period to man’s existence on the globe.”
—Henry David Thoreau (1817–1862)
“Barbarism is the absence of standards to which appeal can be made.”
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