A Timescale is a scale used to represent periods of time ... any animal or plant preserved in the rock record of the Earth that is characteristic of a particular span of geologic time or environment.

The beginning and end of each chunk of time in the geologic time scale is determined by when some species appeared or disappeared from the fossil record. When many species went extinct around the same ...

Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time. Third, magnetism in rocks can be used to estimate the age of ...

Numerical ages estimate the date of a geological event and can sometimes reveal quite precisely when a fossil species existed in time. Third, magnetism in rocks can be used to estimate the age of ...

International Commission on Stratigraphy Includes a global Geologic Time Scale as ratified by the International Commission on Stratigraphy ... Earth Observatory Discusses the first person to use ...