Earth's Greatest Catastrophes Seem to Follow a Mysterious 27-Million-Year Pulse : ScienceAlert

Earth's Greatest Catastrophes Seem to Follow a Mysterious 27-Million-Year Pulse

Nature28 July 2026By Esra Öz

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Earth seen from the Moon during the Artemis II mission. (NASA)

Mass extinctions. Giant volcanic eruptions. Oceans suddenly deprived of oxygen.<br>At first glance, Earth's biggest geological disasters seem to have little in common beyond their sheer scale.

But for decades, scientists have wondered whether these seemingly unrelated events might actually follow a hidden rhythm stretching back hundreds of millions of years.

The possibility that Earth's geological history follows a long-term rhythm has been debated for decades.

The idea dates back to studies published in the 1980s, when researchers first proposed that mass extinctions and other major geological events might recur at regular intervals. Earlier studies identified similar periodic patterns, but the idea has remained controversial.

Now, an analysis published in Evolving Earth revisits that evidence using updated geological timescales and statistical methods.

The analysis concludes that the evidence for a roughly 27.5-million-year geological cycle has continued to strengthen, suggesting many of Earth's largest upheavals may be linked by long-term processes rather than representing isolated catastrophes.

Drawing on previously published geological datasets, New York University geologist Michael Rampino re-examined 89 major geological events spanning the past 260 million years using updated geological ages and statistical analyses.

The dataset includes marine mass extinctions, oceanic anoxic events, continental flood-basalt eruptions, sea-level fluctuations, terrestrial tetrapod extinctions, changes in seafloor spreading rates, and pulses of intraplate volcanism.

Together, these records reveal a dominant periodicity of approximately 27.5 million years, alongside a weaker cycle of around 8.9 million years.

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Rather than proposing that one geological catastrophe directly causes another, the new analysis suggests that multiple Earth systems may periodically respond to the same underlying processes operating over tens of millions of years.

Exactly what those processes are remains uncertain.

The analysis also explores possible drivers of this long-term rhythm.

One possibility lies deep within Earth itself.

The planet's mantle is constantly circulating through convection, albeit at an almost unimaginably slow pace. Periodic changes in mantle convection, or the initiation of mantle plumes, could influence volcanism, plate tectonics, mountain building, and other large-scale geological processes.

Because these systems are closely interconnected, disturbances originating deep within Earth could eventually ripple through the planet's surface, oceans, climate, and biosphere.

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Another hypothesis focuses on interactions between Earth's surface and interior.

Long-term orbital variations influence climate and sea level, periodically redistributing enormous amounts of water, ice, and sediment across the planet. Rampino discusses the possibility that these changing surface loads subtly modify stresses within Earth's crust and upper mantle, potentially influencing tectonic and volcanic activity over geological timescales.

Rampino also considers possible influences beyond Earth, an idea he has been weighing up since the 1980s.

As the Solar System orbits the center of the Milky Way, it oscillates above and below the galaxy's mid-plane, with the timing of these passages aligning with that of Earth's major upheavals. These crossings, other researchers have suggested, could also gravitationally perturb comets in the distant Oort Cloud, increasing the likelihood of large asteroid impacts.<br>The best-determined ages of geological events (red bars), environmental crises (green bars), and mass extinctions (asterisks and stars) over the last 260 million years appear to align with Earth crossing the Galactic mid-plane (dotted line) about every 32 million years. (Rampino, Evolving Earth, 2026)Another, even more speculative, hypothesis suggests that if dark matter is concentrated near the galactic plane, a fraction of it could occasionally be captured by Earth.

Over millions of years, this process could generate small amounts of internal heat, potentially influencing geological activity.

At present, however, there is no direct evidence supporting either mechanism, so they remain very controversial.

Large asteroid impacts are discussed separately in the paper....