SUMMARYA new analysis of 89 major geological events over the past 260 million years found that mass extinctions, volcanic eruptions, ocean crises, and other upheavals may cluster around a roughly 27.5-million-year cycle. Researchers proposed possible causes ranging from mantle convection and orbital changes to speculative galactic influences, but no direct evidence establishes a mechanism. Large asteroid impacts were not included in the statistical test, though several major craters appear to fit the same timing pattern.
A new analysis of 89 major geological events over the past 260 million years found evidence that mass extinctions, volcanic eruptions, ocean crises, and other upheavals may cluster around a roughly 27.5-million-year cycle. The cause remains unknown, with possibilities ranging from mantle activity and orbital changes to speculative galactic influences. Slashdot reader alternative_right shares a report from ScienceAlert: 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.
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. [New York University geologist Michael 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.
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. Although they were not included in the statistical analysis of the 89 geological events, the timing of several of Earth's largest known impact craters appears broadly consistent with the proposed 27.5-million-year rhythm, as Rampino has discussed in earlier papers. Rampino suggests this correspondence may warrant further investigation, but stops short of claiming a causal relationship.