Geologic Time Scale Calculator
Look up the geologic period, era, and eon for any age in millions of years ago (Ma) using the international geologic time scale.
Inputs
Results
Geologic Period
Jurassic
Era
Mesozoic
EonPhanerozoic
Input Age150 Ma
Age in Years150,000,000
Period Start201.4 Ma
Period End145 Ma
Period Duration56.4 My
Position in Period91.1%
% of Earth History3.26%
How to Use This Calculator
- Enter the Age in Ma (millions of years ago) for the rock, fossil, or event you are studying.
- Review the Geologic Period, Era, and Eon — the calculator places your age in the geologic time scale.
- Check Period Start and End dates and Position in Period to understand relative placement.
- Use Earth Age Percentage to put the event in context of Earth's 4.5-billion-year history.
- Compare Period Duration to understand whether your rock formed during a long or short interval.
What each input means
- Age (Ma — millions of years ago)
- Enter the age in millions of years ago (Ma). Earth formed ~4,600 Ma ago. Dinosaurs: ~66–230 Ma.
How this is calculated
Worked example, using the default values
- Identify Input ParametersAge (Ma — millions of years ago) = 150 = 1 input(s) provided
- Calculate Geologic PeriodGeologic Period = matchedPeriod.nameJurassic = Jurassic
- Calculate EraMesozoic = Mesozoic
- Calculate EonPhanerozoic = Phanerozoic
- Calculate Input AgeInput Age = 150150 = 150
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