List of time periods

From Wikipedia, the free encyclopedia - View original article

Jump to: navigation, search

The categorization of time into discrete named blocks is called periodization. This is a list of such named time periods as defined in various fields of study. Major categorization systems include cosmological (concerning the various time periods in the origin and evolution of the Universe), geological (concerning time periods in the origin and evolution of earth) and historical (concerning time periods in the origin and human evolution).

Human time periods[edit]

These can be divided broadly into prehistorical (before history began to be recorded) and historical periods (when written records began to be kept).

Further information: List of archaeological periods

In archaeology and anthropology, human prehistory is subdivided around the three-age system. This list includes the use of the three-age system as well as a number of various designation used in reference to sub-ages within the traditional three.

The dates for each age can vary by region. On the geologic time scale, the Holocene epoch starts at the end of the last glacial period of the current ice age (around 10,000 BC) and continues to the present. The beginning of Mesolithic is usually considered to correspond to the beginning of the Holocene epoch.

Historical periods[edit]

Main article: History by period

The Americas[edit]

Southeast Asia[edit]

Further information: History of Southeast Asia


Further information: History of China

Central Asia[edit]

Further information: History of Mongolia


Further information: History of Egypt


Further information: History of Europe


Further information: History of India


Further information: History of Japan

Middle East[edit]

Further information: History of the Middle East, History of Mesopotamia and Islamic period

Contemporary historical periods throughout the world[edit]

Mythological and astrological time periods[edit]

Geologic time periods[edit]

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.

Cosmological time periods[edit]

13.8 billion years ago: The Big Bang Theory (the universe's beginnings)[edit]

Time PeriodDurationDescription
Planck epochFrom the start to 10−43 seconds after the Big BangVery little concrete information is known about this epoch. Different theories propose different views on this particular time.
Grand unification epochBetween 10−43 to 10−36 seconds after the Big BangThe result of the universe expanding and cooling down during the Planck epoch.
Electroweak epochBetween 10−36 seconds to 10−12 seconds after the Big BangThe universe cools down to 1028 kelvin.
Inflationary epochBetween 10−36 seconds to 10−32 seconds after the Big BangThe shape of the universe flattens due to cosmic inflation.
Quark epochBetween 10−12 seconds to 10−6 seconds after the Big BangCosmic inflation has ended. Quarks are present in the universe at this point.
Hadron epochBetween 10−6 seconds to 1 second after the Big BangThe universe has cooled enough for quarks to form hadrons, protons, neutrons.
Lepton epochBetween 1 second to 10 seconds after the Big BangMost hadrons and anti-hadrons annihilate each other, leaving behind leptons and anti-leptons.
Photon epochBetween 10 seconds to 380,000 years after the Big BangMost leptons and anti-leptons annihilate each other. The universe is dominated by photons.
NucleosynthesisBetween 3 minutes to 20 minutes after the Big BangThe temperature of the universe has cooled down enough to allow atomic nuclei to form via nuclear fusion.
RecombinationAbout 377,000 years after the Big BangHydrogen and helium atoms form.
ReionizationBetween 150 million and 1 billion years after the Big BangThe first stars and quasars form due to gravitational collapse.

See also[edit]


  1. ^ Bowman 2000, pp. 118-161.
Works Cited