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This work assessed the geologic history of the currently defined eons and eras of the pre-Cambrian, [note 2] and the proposals in the "Geological Time Scale" books 2004, [74] 2012, [5] and 2020. [75] Their recommend revisions [4] of the pre-Cryogenian geologic time scale were (changes from the current scale [v2023/09] are italicised):
Geologic time is the timescale used to calculate dates in the planet's geologic history from its origin (currently estimated to have been some 4,600 million years ago) to the present day. Radiometric dating measures the steady decay of radioactive elements in an object to determine its age. It is used to calculate dates for the older part of ...
The Precambrian includes approximately 90% of geologic time. It extends from 4.6 billion years ago to the beginning of the Cambrian Period (about 539 Ma). It includes the first three of the four eons of Earth's prehistory (the Hadean, Archean, and Proterozoic) and precedes the Phanerozoic eon. [6]
The geological time scale (GTS), as defined by international convention, [3] depicts the large spans of time from the beginning of the Earth to the present, and its divisions chronicle some definitive events of Earth history. Earth formed around 4.54 billion years ago, approximately one-third the age of the universe, by accretion from the solar ...
The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, the most recent period is expanded in the fourth timeline, and the most ...
[2] [3] [4] [8] Because it was thought that there was only one significant ash bed, not three of them, any nonglacial deposit containing an ash bed, regardless of its true age, were thought to be the same age. As a result, the nonglacial deposits attributed in the scientific literature as dating to the Yarmouthian (Yarmouth) Interglacial (Stage ...
[2] [3] [4] Two or more radiometric methods can be used in concert to achieve more robust results. [5] Most radiometric methods are suitable for geological time only, but some such as the radiocarbon method and the 40 Ar/ 39 Ar dating method can be extended into the time of early human life [6] and into recorded history. [7]
A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries. Rock series are divided into stages, just as geological epochs are divided into ages. Stages are divided into smaller stratigraphic units called chronozones or substages, and added together into superstages. [2]