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An eon is the largest geochronologic time unit and is equivalent to a chronostratigraphic eonothem. [13] There are four formally defined eons: the Hadean, Archean, Proterozoic and Phanerozoic. [2] An era is the second largest geochronologic time unit and is equivalent to a chronostratigraphic erathem.
13 wrz 2024 · The geologic time scale is the “calendar” for events in Earth history. It subdivides all time into named units of abstract time called—in descending order of duration— eons, eras, periods, epochs, and ages.
28 lut 2020 · Eons are divided into eras, which are further divided into periods, epochs, and ages. Geologic dating is extremely imprecise. For example, although the date listed for the beginning of the Ordovician period is 485 million years ago, it is actually 485.4 with an uncertainty (plus or minus) of 1.9 million years.
The great Precambrian expanse of time is divided into the Proterozoic, Archean, and Hadean eons in order of increasing age. The names of the eras in the Phanerozoic eon (the eon of visible life) are the Cenozoic ("recent life"), Mesozoic ("middle life") and Paleozoic ("ancient life").
18 mar 2020 · This table shows the highest-level units of the geologic time scale: eons and eras. Where available, the names link to more detailed descriptions or significant events that occurred during that specific eon or era.
A major task for the world stratigraphical community has been to establish a single, universal scheme for the subdivision of geological time. There is agreement at the levels of eon, era and (for the most part) period, but regional terms continue to be widely used at the lower hierarchical levels.
28 maj 2024 · Key Takeaways. The geological time scale divides the history of the Earth based on life-forms that have existed during specific times. Geochronologic units include Eons, Eras, Periods, and Epochs. The earliest time of the Earth is divided into Hadean, Archean, and Proterozoic Eon, while the present day belongs to the Phanerozoic Eon.
