🪨 Earth science

Geological Time Scale Converter

Convert an age in years, ka, Ma or Ga into geological time, and see which eon, era, period and epoch it falls in. Press Convert.

Written and reviewed by SM Arijul Islam · Last reviewed 28 October 2026 · Editorial standards · Report an error

About the Geological Time Scale Converter

Geologists measure deep time in millions of years (Ma) and billions of years (Ga). The geological time scale divides that span into nested intervals: eons, eras, periods and epochs. The boundaries are defined by changes in the rock record — first appearances, extinctions and magnetic reversals — not by evenly spaced arithmetic.

The Phanerozoic eon, the time of visible animal life, covers only the last 541 million years. Before that are the Proterozoic, Archean and Hadean. A dinosaur from 66 Ma falls at the boundary between the Cretaceous and Paleogene; a trilobite from 500 Ma is in the Cambrian. This tool places an age in the standard international chart.

How the calculation works

1 ka = 1,000 years; 1 Ma = 1,000,000 years; 1 Ga = 1,000,000,000 years.
The Phanerozoic eon began 541 Ma.
The Cenozoic era began 66 Ma; the Quaternary period began 2.58 Ma.
The Holocene epoch began 11,700 years ago (0.0117 Ma).

Reference values

Major intervals used by the converter
Interval	Rank	Start (Ma)	End (Ma)
Hadean	Eon	4,600	4,000
Archean	Eon	4,000	2,500
Proterozoic	Eon	2,500	541
Phanerozoic	Eon	541	0
Paleozoic	Era	541	252.17
Mesozoic	Era	252.17	66
Cenozoic	Era	66	0
Cretaceous	Period	145	66
Jurassic	Period	201.3	145
Triassic	Period	252.17	201.3
Quaternary	Period	2.58	0

Worked example: placing three fossils

A rock dated 300 Ma is in the Carboniferous period, late Paleozoic era. A dinosaur at 66 Ma sits at the Cretaceous–Paleogene boundary, the extinction that ended the non-avian dinosaurs. A human fossil at 0.3 Ma is in the Pleistocene. The whole of recorded history is less than 0.00001 Ga.

The boundaries are not evenly spaced; they mark changes in the rock record. That is why a geological timetable is a set of agreed divisions rather than a simple arithmetic scale. When a date sits close to a boundary, check the current chart instead of rounding to the nearest period.

Frequently asked questions

What does Ma mean?

Mega-annum: one million years before present. It is a duration/age unit, not a date on a calendar.

Why do the boundaries keep changing?

International commissions refine them as radiometric dates and stratigraphic evidence improve. The figures here follow the current ICS chart to two decimal places where relevant.

Is the Anthropocene an epoch?

It has been proposed and debated but is not part of the current official chart. The Holocene remains the formal epoch.

Why do geological dates keep changing?

Boundaries are refined as radiometric dates and fossil evidence improve. The International Chronostratigraphic Chart is updated periodically, and this page uses the current published values.

Sources and standards

Period and epoch boundaries follow the International Chronostratigraphic Chart published by the International Commission on Stratigraphy. Ages are given in millions of years before present with the chart's own uncertainty, and the page does not interpolate beyond the published boundaries.

International Commission on Stratigraphy — Chronostratigraphic Chart