What does Ma mean in geology?

Ma stands for megaannum, Latin for "one million years." It is the most common unit for expressing geologic ages and durations. For example, the Cretaceous period ended approximately 66 Ma ago.

What is the difference between Ma and Ga?

Ma (megaannum) equals one million years, while Ga (gigaannum) equals one billion years — so 1 Ga = 1,000 Ma. Ga is used for very ancient events such as Earth's formation (roughly 4.54 Ga ago).

What does ka mean in geologic time?

ka stands for kiloannum, meaning one thousand years. It is used for relatively recent geologic events such as the last glacial maximum (~21 ka ago) or early human migrations.

How accurate are these conversions?

The unit conversions are mathematically exact (1 Ma = 1,000,000 years by definition). The boundary ages in the reference table follow the 2023 International Chronostratigraphic Chart published by the ICS, and are rounded to three significant figures for clarity.

What is the oldest eon on Earth?

The Hadean eon is informally the oldest, spanning from Earth's formation (~4,540 Ma ago) to ~4,000 Ma ago. It is not formally defined by the ICS but is widely used in educational and scientific contexts.

Can I convert negative (future) values?

Yes. The converter accepts negative numbers, which by convention represent time in the future. Positive values represent time in the past (before present).

Geologic Time Converter

Name: Geologic Time Converter
Availability: InStock
Author: Nham Vu

Convert geologic time units (Ma, Ga, ka) to and from standard time units, and browse the geologic time scale reference table.

Unit Converter

Enter a value in any unit — all others update instantly.

Click any row to load that age into the converter. Ages follow the 2023 ICS chart.

Eon	Era	Period / Epoch	Start (Ma)	Duration (Ma)

Symbol	Full Name	Equals (years)
Ga	Gigaannum	1,000,000,000
Ma	Megaannum	1,000,000
ka	Kiloannum	1,000
yr	Year	1
dec	Decade	10
cent	Century	100
mil	Millennium	1,000

Notation note

Geologic ages are measured as "before present" (BP), where "present" is conventionally set to 1950 CE. A positive Ma/Ga/ka value therefore refers to the past. Negative values are sometimes used for future projections.

Copied!

Summary

Convert geologic time units (Ma, Ga, ka) to and from standard time units, and browse the geologic time scale reference table.

How it works

Select the input unit (Ma, Ga, ka, years, decades, centuries, or millennia).
Type the numeric value you want to convert.
All equivalent values in every other unit update instantly.
Use the "Geologic Time Scale" tab to look up eons, eras, periods, and epochs.
Click any row in the reference table to pre-fill the converter with that age.
Copy any result with the copy icon next to each output field.

Use cases

Translate Ma/Ga/ka values from scientific papers into intuitive time spans.
Cross-check dates when reading about the dinosaur era, ice ages, or Earth formation.
Educational aid for geology, paleontology, or Earth science students.
Quick reference when comparing different geologic periods side by side.
Convert radiometric dating results between common notation styles.
Understand deep-time values cited in climate science and astronomy.
Look up when a specific geologic period started and how long it lasted.
Confirm unit conversions before including them in reports or articles.

Frequently Asked Questions

Related tools

Age Calculator Radiometric Dating Calculator Half Life Calculator

Last updated: 2026-05-23 · Reviewed by Nham Vu