Erathem
In stratigraphy, paleontology, geology, and geobiology an erathem is the total stratigraphic unit deposited during a certain corresponding span of time during an era in the geologic timescale.
It can therefore be used as a chronostratigraphic unit of time which delineates a large span of years – less than a geological eon, but greater than its successively smaller and more refined subdivisions. By 3,500 million years ago simple life had developed on earth. The atmosphere was a mix of noxious and poisonous gases.
These simple organisms, Cyanobacteria ruled the still cooling earth for approximately a thousand million years and gradually transformed the atmosphere to one containing free oxygen. These changes, along with tectonic activity left chemical trails and other physical clues in the rock record, and it is these changes along with the later richer fossil record which specialists use to demarcate times early in planet earth's history in various disciplines.
Erathems are not often used in practice. While they are subdivisions of eonothems and are themselves subdivided into systems, dating experts prefer the finer resolution of smaller spans of time when evaluating strata.
Erathems have the same names as their corresponding eras.
Similarly, the Proterozoic eonothem is divided youngest to oldest into theMultidiscipline comparison
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