Study Identifies 27.5‑Million‑Year Cycle in Earth's Mass Extinctions

Geologist Michael Rampino of New York University and his co‑authors analysed 89 major geological and biological events spanning the last 260 million years. Their statistical assessment, published in the journal Evolving Earth, shows that mass extinctions, large volcanic eruptions, asteroid impacts and related phenomena tend to cluster around intervals of roughly 27.5 million years, with weaker signals near 9 million years and 250 million years.

The researchers suggest the pattern could be linked to the Solar System’s periodic crossings of the Milky Way’s galactic plane, which might disturb distant comet reservoirs. The hypothesis remains controversial; many scientists argue that the apparent periodicity may result from selection bias or insufficient data, and the study does not claim that a future extinction is imminent.

The work revives a long‑standing debate in geology about whether Earth’s most dramatic crises follow a regular timetable or occur randomly.