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See also: Geologic Timescale (table)Geologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
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unit of geologic time that is a subdivision of a period. The Pleistocene and Holocene epochs, for example, are divisions of the Quaternary period. Epoch is also used to describe a short length of geologic time during a special occurrence, such as the glacial epoch. See geologygeology,
science of the earth's history, composition, and structure, and the associated processes. It draws upon chemistry, biology, physics, astronomy, and mathematics (notably statistics) for support of its formulations.
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; Geologic TimescaleGeologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
..... Click the link for more information.
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An arbitrary fixed date or instant of time that is used as a reference datum, especially for stellar coordinates and orbital elements. For example, the coordinates right ascension and declination are continuously changing, primarily as a result of the precession of the equinoxes. Coordinates must therefore refer to a particular epoch, which can be the time of an observation, the beginning of the year in which a series of observations of an object was made, or the beginning of a half century. The standard epoch specifies the reference system to which coordinates are referred. Coordinates of star catalogs commonly referred to the mean equator and equinox of the beginning of a Besselian year. Since 1984 the Julian year has been used: the current standard epoch, designated J2000.0, is 2000 Jan. 1.5; it is exactly one Julian century removed from the standard epoch of 1900 Jan 0.5. Epochs for the beginning of a year now differ from the standard epoch by multiples of the Julian year. A standard epoch is usually retained for 50 years.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006


A particular instant for which certain data are valid; for example, star positions in an astronomical catalog, epoch 1950.0.
A major subdivision of a period of geologic time.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


1. Astronomy a precise date to which information, such as coordinates, relating to a celestial body is referred
2. Geology a unit of geological time within a period during which a series of rocks is formed
3. Physics the displacement of an oscillating or vibrating body at zero time
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


(operating system)
(Probably from astronomical timekeeping) A term used originally in Unix documentation for the time and date corresponding to zero in an operating system's clock and timestamp values.

Under most Unix versions the epoch is 1970-01-01 00:00:00 GMT; under VMS, it's 1858-11-17 00:00:00 (the base date of the US Naval Observatory's ephemerides); on a Macintosh, it's 1904-01-01 00:00:00.

System time is measured in seconds or ticks past the epoch. Weird problems may ensue when the clock wraps around (see wrap around), which is not necessarily a rare event; on systems counting 10 ticks per second, a signed 32-bit count of ticks is good only for 0.1 * 2**31-1 seconds, or 6.8 years. The one-tick-per-second clock of Unix is good only until 2038-01-18, assuming at least some software continues to consider it signed and that word lengths don't increase by then. See also wall time.


(Epoch) A version of GNU Emacs for the X Window System from NCSA.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)


The starting date from which time is measured as a number of days or minutes or seconds, etc. In computer applications, epochs are used to maintain a time reference as a single number for ease of computation. Otherwise, depending on the granularity of time desired, every point in time would have to be stored with some of or all of the components of the time hierarchy, including year, month, day, hour, minute, second, millisecond, microsecond and nanosecond. Following are the various epochs in use. See also EPOC.

System          Epoch            Measured in

  Unix/Linux      Jan. 1, 1970     Seconds
  Java            Jan. 1, 1970     Milliseconds

  Windows files   Jan. 1, 1601     Ticks (100 ns)
  Windows dates   Jan. 1, 0001     Ticks (100 ns)

  Mac             Jan. 1, 2001     Seconds
  Earlier Mac     Jan. 1, 1904     Seconds

  Excel           Dec. 31, 1899    Days
  DB2             Dec. 31, 1899    Days

  Unununium       Jan. 1, 2000     Microseconds

No USB Drives in 1969
When this USB drive was formatted, the date was reset to the epoch. The 7:00pm tells us it was done on the East Coast, five hours behind the UTC time of January 1, 1970 (see above). This info comes from the Mac that the drive was plugged into.
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References in periodicals archive ?
According to [3, 20], in P300 Speller BCI, a target EEG epoch is among the consecutive EEG epochs that are overlapped on one another so that nontarget EEG epochs could also contain P300 waveform just in a bit different time range, compared to target EEG epochs.
If eventually approved by the International Commission on Stratigraphy--the gatekeepers of geologic time--and the Executive Committee of the International Union of Geological Sciences, the Anthropocene would cut short the Holocene Epoch, which has reigned since the end of the last glacial period around 11,700 years ago.
A host of factors have apparently taken Earth into this new epoch. "The warming temperature, higher sea levels, ash from fossil fuels, plastic waste, a dramatic increase in erosion, the spread of animal species around the world and radioactive particles left around the world from nuclear bomb tests would all contribute to permanent changes in the Earth's rocks, the scientists said," (http://www.independent.co.uk/environment/anthropocene-epoch-new-planet-earth-man-made-what-is-it-a7215116.html) wrote the Independent.
* discontinuity in height difference data ("jumps") --quasi constant change of height difference in subsequent epochs in relation to previous epochs.
In the overall cohort, the rate was 27.7% in epoch 1 and 45.4% in epoch 4.
The mean age of onset was 80 years in epoch 1, 82 in epoch 2, 84 in epoch 3, and 85 in epoch 4.
Data collected in 5 s epochs were down sampled into 10, 20, 30, and 60 s sampling epochs to investigate the effect of sampling frequency.
Please don't tell me that I'm wrong, and that every epoch sets the tempo in a way that is audible only to future generations.
AS THE HUMAN IMPACT on Earth "cut to the very bone" of deep time, as some have claimed, effectively ending the Holocene Epoch and ushering in what should be called the Anthropocene?
Note that, this pattern also contains two epochs, i.e., the epoch that the node reaches the interrupted point and the epoch that the node moves to a randomly chosen new destination.
The Eemian Interglacial was the last interglacial epoch before the current one, the Holocene.