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Geologic Time Scale Chart and Age Calculator

The geologic time scale is the shared international framework geologists use to organize 4,567 million years of Earth history. The geochronologic hierarchy moves from eon to era, period, epoch, and age; corresponding bodies of rock use the chronostratigraphic terms eonothem, erathem, system, series, and stage. This reference follows the International Commission on Stratigraphy's International Chronostratigraphic Chart version 2024/12. Ma means mega-annum and is used for a numerical age in millions of years before present, while Myr is commonly used for a duration of millions of years. The Phanerozoic eon begins at 538.8 Ma. Its Paleozoic era contains the Cambrian from 538.8 to 486.85 Ma, Ordovician from 486.85 to 443.1 Ma, Silurian from 443.1 to 419.62 Ma, Devonian from 419.62 to 358.86 Ma, Carboniferous from 358.86 to 298.9 Ma, and Permian from 298.9 to 251.902 Ma. The Mesozoic contains the Triassic from 251.902 to 201.4 Ma, Jurassic from 201.4 to 143.1 Ma, and Cretaceous from 143.1 to 66 Ma. The Cenozoic contains the Paleogene from 66 to 23.04 Ma, Neogene from 23.04 to 2.58 Ma, and Quaternary from 2.58 Ma to the present. Cenozoic epochs include the Paleocene from 66 to 56 Ma, Eocene from 56 to 33.9 Ma, Oligocene from 33.9 to 23.04 Ma, Miocene from 23.04 to 5.333 Ma, Pliocene from 5.333 to 2.58 Ma, Pleistocene from 2.58 to 0.0117 Ma, and Holocene from 0.0117 Ma to the present. Precambrian is a widely used informal umbrella rather than one formal eon. The Proterozoic eon spans 2,500 to 538.8 Ma and includes the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic eras and the Siderian, Rhyacian, Orosirian, Statherian, Calymmian, Ectasian, Stenian, Tonian, Cryogenian, and Ediacaran periods. The Archean spans 4,031 to 2,500 Ma in the 2024/12 chart and includes the Eoarchean, Paleoarchean, Mesoarchean, and Neoarchean eras. The Hadean spans 4,567 to 4,031 Ma. In the Phanerozoic and Ediacaran, numerical ages do not usually provide the formal definition of a unit: ratified Global Boundary Stratotype Section and Points, or GSSPs, define lower boundaries, and numerical calibrations can be revised. Older textbooks may therefore show different numbers. GeoMiner's free calculator translates a supplied age from 0 to 4,567 Ma into the current broad hierarchy and shows its position on a scaled 24-hour Earth clock. It does not date a rock, fossil, mineral, map unit, or ph

Verification resources

Cross-check terminology, classification, methods, and safety with these authoritative external resources.

  • undefined. Current international names, hierarchy, numerical boundary ages, GSSP and GSSA status, and the warning that Phanerozoic numerical ages are revised estimates rather than the formal definitions of units.
  • undefined. The maintained online chart, interval hierarchy, multilingual terminology, boundary information, and current chart attribution.
  • undefined. An educational explanation of why geologists divide Earth history into named intervals and how the scale is refined as evidence and dating improve.
  • undefined. A public geologic-time reference and explanation of standardized divisions used to communicate Earth history.

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Common questions

What is the geologic time scale?
It is the internationally standardized hierarchy geologists use to organize Earth history. From largest to smaller units, the main geochronologic ranks are eon, era, period, epoch, and age. The corresponding rock-record terms are eonothem, erathem, system, series, and stage.
What does Ma mean in geology?
Ma means mega-annum, or one million years, and is used here for a numerical age before present. A span lasting millions of years is often written Myr. This calculator accepts ages from the present to 4,567 Ma.
Are numerical dates the formal definitions of periods?
Not usually in the Phanerozoic and Ediacaran. The ICS chart explains that ratified Global Boundary Stratotype Section and Points, or GSSPs, formally define those lower boundaries; numerical ages are calibrated estimates that can be revised.
Why do some older charts show different dates?
Boundary estimates change as stratigraphic correlation, radiometric dating, and international decisions improve. Always state the chart version used. This page follows the International Chronostratigraphic Chart v2024/12.
Can a rock's age be identified from appearance alone?
No. A rock name, fossil-like shape, colour, or texture does not establish an age. Reliable age work needs field relationships and may use fossils, stratigraphic correlation, radiometric methods, paleomagnetism, or other qualified evidence.

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