Geologic Time Scale Converter

Convert an age in millions of years ago (Ma) to its corresponding eon, era, period, epoch, and stage on the geologic time scale — or jump to an interval and see its age range.

Interactive Geologic Time Converter

Valid range: 0 (present day) to 4,600 Ma (approximate age of Earth).

Eon

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Era

–

Period

–

Epoch

–

Stage (if defined)

–

Age range: –

Or start from a named interval and see its age range:

Condensed Geologic Time Scale

Scroll horizontally to explore

Bars are proportional to duration in Ma (logically, not to exact scale). Click a bar to fill the converter with its mid‑point age.

How the geologic time scale converter works

Geologists divide Earth’s 4.6‑billion‑year history into nested time units: eons, eras, periods, epochs, and stages. This converter lets you move back and forth between a numeric age in millions of years ago (Ma) and those named intervals.

1. Converting an age (Ma) to eon, era, period and epoch

When you type an age in Ma, the tool searches a structured table of time intervals, starting from the finest level (stage) and working up:

Logic

  • Find the interval where startMa ≥ age > endMa.
  • If several levels match (e.g., stage, epoch, period), the calculator returns the full hierarchy.
  • The mid‑point age of the interval is used when you click on a bar in the timeline.

For example, an age of 66 Ma falls in the Phanerozoic eon, Cenozoic era, Paleogene period, and Paleocene epoch.

2. Converting from interval name to age range

The dropdown menus work in the opposite direction. When you pick an eon, era, period, or epoch, the converter:

  • Looks up the interval’s official start and end ages (rounded to Ma).
  • Displays the age range and duration in millions of years.
  • Highlights the interval in the horizontal timeline.

3. Data sources and precision

The boundaries used here are based on the International Commission on Stratigraphy (ICS) geologic time scale, simplified and rounded to one decimal place where appropriate.

For teaching, field work, and most general geology applications, these rounded values are more than adequate. For high‑precision stratigraphic or geochronologic research, always consult the latest official ICS charts and primary literature.

Key units of geologic time

  • Eon – the largest commonly used unit (e.g., Hadean, Archean, Proterozoic, Phanerozoic).
  • Era – subdivisions of eons (e.g., Paleozoic, Mesozoic, Cenozoic).
  • Period – classic textbook units like Cambrian, Jurassic, Cretaceous, Quaternary.
  • Epoch – finer slices within periods (e.g., Pleistocene, Holocene).
  • Stage – the finest standard global units, often tied to specific stratotype sections.

Why Ma (millions of years ago)?

Geologic time is so vast that using years would produce unwieldy numbers. Instead, ages are expressed in Ma (mega‑annum, million years ago). For instance:

  • 0 Ma – present day (Holocene epoch).
  • 2.58 Ma – base of the Pleistocene.
  • 66.0 Ma – Cretaceous–Paleogene (K–Pg) boundary and dinosaur extinction.
  • 541 Ma – base of the Phanerozoic and Cambrian explosion.

Frequently asked questions

What is a geologic time scale converter?

It is a tool that lets you translate between numeric ages (in millions of years ago, Ma) and the named intervals of the geologic time scale, such as eons, eras, periods, and epochs. This is useful for students, teachers, and geoscientists who need a quick reference without manually consulting charts.

Which time scale does this calculator follow?

The converter follows a simplified version of the International Commission on Stratigraphy (ICS) global geologic time scale. Boundary ages are rounded to commonly cited Ma values, which makes the tool easy to use in classrooms and field notes while still reflecting modern stratigraphic standards.

Why doesn’t my age fall exactly on a boundary?

Most ages you enter will fall somewhere within an interval, not exactly at its start or end. The converter simply finds the interval whose age range contains your value. If you need to know the precise boundary age, consult the ICS chart and associated references, which list uncertainties and dating methods.

Can I use this for local or regional stages?

This tool focuses on the international (global) chronostratigraphic units. Many regions have additional local stages or informal units that are not included here. For regional stratigraphy, you may need to cross‑reference local charts with the global ICS scale.