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This is a list of named time periods defined in various fields of study.

Cosmological time periods


Because of the scales involved (both very large and very small), cosmological time periods are usually described in seconds. In this table, each row is defined in seconds after the Big Bang, with earliest at the top of the chart.

Seconds after Big Bang Period
to 5.4 × 10−44 Planck time
10−43 to 10−35 Planck Epoch
10−35 to 10−33 Inflationary epoch
10−35 to 10−12 Epoch of Grand Unification
10−12 to 10−6 Electroweak Epoch
10−6 to 100 Hadron Epoch
100 to 102 Lepton Epoch
102 to 1013 Epoch of Nucleosynthesis
1013 on Epoch of Galaxies

The present time is approximately 4.3 x 1017 seconds after the Big Bang; the Sun and Earth were created about 2 x 1017 seconds after the Big Bang. 1020 seconds is 3 trillion years in the future.

Geologic time periods


The geologic time scale covers the extent of the existence of Earth, from about 4600 million years ago to the present day. It is marked by Global Boundary Stratotype Sections and Points. Geologic time units are (in order of descending specificity) eons, eras, periods, epochs, and ages; and the corresponding chronostratigraphic units, which measure "rock-time", are eonothems, erathems, systems, series, and stages.

The second and third timelines are each subsections of their preceding timeline as indicated by asterisks. The Cenozoic is sometimes divided into the Quaternary and Tertiary periods, although their use is no longer official.

Human time periods


The human timescale covers the time that humans have existed, usually taken to be from about 250,000 years ago - when homo sapiens began to develop. It is broadly divided into prehistorical (before history began to be recorded) and historical periods (when written records began to be kept).

Prehistorical periods

In archaeology and anthropology, prehistory is subdivided around the three-age system.

The dates for each age can vary by region, although the beginning of Mesolithic is usually considered to correspond to the beginning of the Holocene epoch on the geologic time scale.

Historical periods

Calendar systems

Various societies in the past all over the world have created calendars to record events, such as religious dates and other celebrations. A common characteristic of most of the known calendars is that they count years from some point in history, either known or unknown. This of course leads to a calendar based periodization. Most commonly known is the christian time calendar, with its time before and after Christ. Others are the Islamic and Jewish calendars.

Mythological and astrological time periods

Specialist human periods

See also


History by period | Timelines

Periodisierung | Histoire (périodes) | Történelmi korszakok | Periodizacija zgodovine | Çağ

 

This article is licensed under the GNU Free Documentation License. It uses material from the "List of time periods".

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