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 (geologic periods, epochs, and geologic ages). By 3,500 million years ago (Mya) simple life had developed on earth (the oldest known microbial fossils in Australia are dated to this figure). The atmosphere was a mix of noxious and poisonous gases (methane, ammonia, sulfur compounds, etc. – a so-called reducing atmosphere lacking much free oxygen which was bound up in compounds).
These simple organisms, cyanobacteria ruled the still cooling earth for approximately a billion years and gradually transformed the atmosphere to one containing free oxygen. These changes, along with tectonic activity left chemical trails (red bed formation, etc.) and other physical clues (magnetic orientation, layer formation factors) 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. The Phanerozoic eonothem can thus be divided into Cenozoic, Mesozoic, and Paleozoic erathems. Similarly, the Proterozoic eonothem is divided youngest to oldest into the Neoproterozoic, Mesoproterozoic and Paleoproterozoic erathems, and the Archean eon and eonothem are divided similarly into the Neoarchean, Mesoarchean, Paleoarchean and the Eoarchean, for which a lower (oldest) limit is undefined.
See also
Multidiscipline comparison
| Segments of rock (strata) in chronostratigraphy | Time spans in geochronology | Notes to geochronological units |
|---|---|---|
| Eonothem | Eon | 4 total, half a billion years or more |
| Erathem | Era | 10 defined, several hundred million years |
| System | Period | 22 defined, tens to ~one hundred million years |
| Series | Epoch | 38 defined, tens of millions of years |
| Stage | Age | 101 defined, millions of years |
| Chronozone | Chron | subdivision of an age, not used by the ICS timescale |
Related other topics
- Body form
- European Mammal Neogene
- Geologic time scale
- New Zealand geologic time scale
- North American Land Mammal Age
- Fauna (animals)
- Type locality
- List of GSSPs
Notes
- "Rockman's Geologic Time Chart". Retrieved 2008-06-17.
- basis for the Miller–Urey experiment
- "International Chronostratigraphic Chart" (PDF). Geologic TimeScale Foundation. 2005. Retrieved October 23, 2025.
- F.M. Gradstein, J.G. Ogg, A.G. Smith, et al., "A Geologic Time Scale", (2004; Cambridge University Press).
- "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy. December 2024. Retrieved October 23, 2025.
wikipedia, wiki, encyclopedia, book, library, article, read, free download, Information about Erathem, What is Erathem? What does Erathem mean?