From Wikipedia, the free encyclopedia - View original article
|This article needs additional citations for verification. (July 2013)|
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).
These can be divided broadly into prehistorical (before history began to be recorded) and historical periods (when written records began to be kept).
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.
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.
|Planck epoch||From the start to 10−43 seconds after the Big Bang||Very little concrete information is known about this epoch. Different theories propose different views on this particular time.|
|Grand unification epoch||Between 10−43 to 10−36 seconds after the Big Bang||The result of the universe expanding and cooling down during the Planck epoch.|
|Electroweak epoch||Between 10−36 seconds to 10−12 seconds after the Big Bang||The universe cools down to 1028 kelvin.|
|Inflationary epoch||Between 10−36 seconds to 10−32 seconds after the Big Bang||The shape of the universe flattens due to cosmic inflation.|
|Quark epoch||Between 10−12 seconds to 10−6 seconds after the Big Bang||Cosmic inflation has ended. Quarks are present in the universe at this point.|
|Hadron epoch||Between 10−6 seconds to 1 second after the Big Bang||The universe has cooled enough for quarks to form hadrons, protons, neutrons.|
|Lepton epoch||Between 1 second to 10 seconds after the Big Bang||Most hadrons and anti-hadrons annihilate each other, leaving behind leptons and anti-leptons.|
|Photon epoch||Between 10 seconds to 380,000 years after the Big Bang||Most leptons and anti-leptons annihilate each other. The universe is dominated by photons.|
|Nucleosynthesis||Between 3 minutes to 20 minutes after the Big Bang||The temperature of the universe has cooled down enough to allow atomic nuclei to form via nuclear fusion.|
|Recombination||About 377,000 years after the Big Bang||Hydrogen and helium atoms form.|
|Reionization||Between 150 million and 1 billion years after the Big Bang||The first stars and quasars form due to gravitational collapse.|