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Reference.org
Geologic time scale
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<p>The geologic time scale or geological time scale (GTS) is a representation of <a href="/facts/Time/HceJKUGB">time</a> based on the <a href="/facts/Geologic_record/37Y1dLN4">rock record</a> of <a href="/facts/Earth/HLLmDfj0">Earth</a>. It is a system of <a href="/facts/Chronological_dating/xYYqj6qK">chronological dating</a> that uses <a href="/facts/Chronostratigraphy/L3XU1Uh3">chronostratigraphy</a> (the process of relating <a href="/facts/Stratum/w5D4VAwa">strata</a> to time) and <a href="/facts/Geochronology/U8hRTGwL">geochronology</a> (a scientific branch of <a href="/facts/Geology/WGvVRIYF">geology</a> that aims to determine the age of rocks). It is used primarily by <a href="/facts/Earth_science/rQsXCSbM">Earth scientists</a> (including <a href="/facts/Geologist/vGc0tBHB">geologists</a>, <a href="/facts/Paleontology/60n5yldd">paleontologists</a>, <a href="/facts/Geophysics/ywVQ1sAQ">geophysicists</a>, <a href="/facts/Geochemistry/05094gDu">geochemists</a>, and <a href="/facts/Paleoclimatology/p3x22QaC">paleoclimatologists</a>) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as <a href="/facts/Lithology/WLIJXzGj">lithologies</a>, <a href="/facts/Paleomagnetism/kDwUXDX5">paleomagnetic</a> properties, and <a href="/facts/Fossil/by7NzIA1">fossils</a>. The definition of standardised international units of geological time is the responsibility of the <a href="/facts/International_Commission_on_Stratigraphy/sGDCGGd2">International Commission on Stratigraphy</a> (ICS), a constituent body of the <a href="/facts/International_Union_of_Geological_Sciences/NfRap9FD">International Union of Geological Sciences</a> (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geological time. The chronostratigraphic divisions are in turn used to define geochronologic units. </p>