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.

The Geologic Time Scale is divided into four eons, ten eras, 22 periods, and several epochs and ages. Each eon, era, period, and epoch is defined by major geological or paleontological events. The eons are the Hadean, Archean, Proterozoic, and Phanerozoic.

Geologic time, the extensive interval of time occupied by the geologic history of Earth. Formal geologic time begins with the Archean Eon (4.0 billion to 2.5 billion years ago) and continues to the present day. Modern geologic time scales also include the Hadean Eon (4.6 billion to 4.0 billion years ago).

2020年2月28日 · Geologic time spans are divided into units and subunits, the largest of which are eons. Eons are divided into eras, which are further divided into periods, epochs, and ages. Geologic dating is extremely imprecise.

2009年2月19日 · eon, Long span of geologic time. In formal usage, eons are the longest portions of geologic time (era s are the second-longest). Three eons are recognized: the Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), the Proterozoic Eon, and the Archean Eon.

2025年1月11日 · Definition: The Geological Time Scale (GTS) organizes Earth’s 4.6 billion-year history into hierarchical units (eons, eras, periods, epochs, and ages) based on geological and fossil records.

This is most easily done by first breaking the time scale into its component parts: eons, eras, periods, and epochs. The eon is the broadest category of geological time.

2023年12月6日 · One of the key concepts of the Geologic Time Scale is the division of time into units of varying lengths. The largest unit is the eon, which is further divided into smaller units such as eras, periods, and epochs. The first eon, the Hadean, lasted from the formation of the Earth until about 4 billion years ago.

2024年12月16日 · The primarily defined divisions of time are eons, the Hadean, the Archean, the Proterozoic and the Phanerozoic. The first three of these can be referred to collectively as the Precambrian supereon. Each eon is subsequently divided into eras, which in turn are divided into periods, which are further divided into epochs.

2021年5月12日 · There are four eons recognized on the geologic timescale: the Hadean Eon (which is the oldest), Archean Eon, Proterozoic Eon, and the Phanerozoic (which is most recent). Each of these eons had a significant difference in climate, the composition of the earth, and the life forms that lived then.