Geological dating wiki
At the same time paleontologists define a system of faunal stages, of varying lengths, based on the kinds of animal fossils found there.In many cases, such faunal stages have been adopted in building the geological nomenclature, though in general there are far more recognized faunal stages than defined geological time units.
The height of each table entry does not correspond to the duration of each subdivision of time.
For example, in North America the Lower Cambrian is called the Waucoban series that is then subdivided into zones based on trilobites.
The same timespan is split into Tommotian, Atdabanian and Botomian stages in East Asia and Siberia.
These discussions were rendered obsolete by the discovery of radioactivity in 1896 by the French physicist Henri Becquerel.
The existence of radioactivities of various kinds in rocks has enabled earth scientists to determine the age of the Earth, the moon, meteorites, mountain chains and ocean basins, and to draw up a reasonably accurate time scale of evolution.