Ma — Glossary — Stratum Study

Mega-annum: million years ago, the unit of absolute age. “~66 Ma” is the Cretaceous–Paleogene boundary; “Myr” is used for a duration (a span of million years).

Sources

International Commission on Stratigraphy — International Chronostratigraphic Chart
Macrostrat — Interval definitions (CC BY 4.0)

Cite this article

Stratum Study. "Ma" (Glossary). Stratum Study pack 2026.09, as of 2026-09-16. https://stratum.black/study/glossary/ma. Accessed 2026-09-20.

BibTeX · CSL-JSON

@misc{stratum-ma,
  title        = {Ma},
  author       = {{Stratum Study}},
  howpublished = {\url{https://stratum.black/study/glossary/ma}},
  year         = {2026},
  note         = {Glossary article, Stratum Study pack 2026.09, as of 2026-09-16; sources: stratum. Accessed 2026-09-20.}
}

Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.