The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history.The tables of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy.The Encyclopedia is available in a four volume printed edition or on CD-ROM containing PDF versions of all four volumes.
Eons are divided into eras, which are in turn divided into periods, epochs and ages.
The following four timelines show the geologic time scale.
The primate fossil record for this crucial transitional period leading to australopithecines is still scanty and somewhat confusing.
However, by about 4.2 million years ago, unquestionable australopithecines were present.
وتتألف هذه الجزيرة من ساحل يمتد على طول 17 كم من المنحدرات الساحليّة الوعرة.
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Il se compose d’une bande étroite de 17 km de long, formée de falaises côtières accidentées.
Originaires des fonds marins, ces falaises, qui datent de la période de l’Édiacarien (580-560 millions d’années), présentent les plus anciens assemblages de grands fossiles connus.
The classification of Sahelanthropus has been the most in question.
The earliest australopithecines very likely did not evolve until 5 million years ago or shortly thereafter (during the beginning of the Pliocene Epoch) in East Africa.
The primary defined divisions of time are eons, in sequence the Hadean, the Archean, the Proterozoic and the Phanerozoic.