eonothem

The geological timescale has all systems in the Phanerozoic eonothem subdivided into series.

As of 2008, the ICS is nearly finished a task begun in 1974, subdividing the Phanerozoic eonothem into internationally accepted stages using two types of benchmark.

In stratigraphy and geology, an eonothem is the totality of rock strata laid down in the stratigraphic record deposited during a certain eon of the continuous geologic timescale.

(A fossil or feature present in the "upper Phanerozoic" eonothem (strata) would be discussed as being dated within the "later Phanerozoic" eon, whereas something found in the middle Phanerozoic could be discussing a layer, stage or the relative time.)

The Eonothem is not to be confused with the eon itself, which is a corresponding division of geologic time spanning a specific amount of (millions of) years, during which rocks were formed that are classified within the eonothem.