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On the geologic time scale, the Holocene epoch starts at the end of the last glacial period of the current ice age (c. 10,000 BC) and continues to the present. The beginning of the Mesolithic is usually considered to correspond to the beginning of the Holocene epoch.
These units are arranged in a hierarchy: eon, era, period, epoch, subepoch, age, and subage. [14] Geochronology is the scientific branch of geology that aims to determine the age of rocks, fossils, and sediments either through absolute (e.g., radiometric dating) or relative means (e.g., stratigraphic position, paleomagnetism, stable isotope ...
c. 2.58 Ma – start of the Pleistocene epoch, the Stone Age and the current Quaternary Period; emergence of the genus Homo. Smilodon , the best known of the sabre-toothed cats , appears. c. 2.4 Ma – The Amazon River takes its present shape in South America.
The Paleogene (alternatively Palaeogene) Period is a unit of geologic time that began 66 and ended 23.03 Ma [9] and comprises the first part of the Cenozoic Era. This period consists of the Paleocene, Eocene and Oligocene Epochs.
Permian period, end of Paleozoic era beginning of Mesozoic era, Triassic period (252–201 Ma) Cycads, seed ferns. First therapsids. Oxygen in atmosphere peaks, around 30%. [33] Gorgonopsians and other therapsids (forerunners of mammals) displace pelycosaurs as dominant land animals. First gorgonopsia, apex predators of the Late Permian.
Geochronological units are periods of time, thus it is correct to say that Tyrannosaurus rex lived during the Late Cretaceous Epoch. [16] Chronostratigraphic units are geological material, so it is also correct to say that fossils of the genus Tyrannosaurus have been found in the Upper Cretaceous Series. [ 17 ]
An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth. [1] Comparable terms are epoch, age, period, saeculum, aeon (Greek aion) [2] and Sanskrit yuga. [3]
c. 10 −43 seconds: Grand unification epoch begins: While still at an infinitesimal size, the universe cools down to 10 32 kelvin. Gravity separates and begins operating on the universe—the remaining fundamental forces stabilize into the electronuclear force, also known as the Grand Unified Force or Grand Unified Theory (GUT), mediated by (the hypothetical) X and Y bosons which allow early ...