Major destructive events on Earth, including mass extinctions and asteroid impacts, may be occurring in a regular, 27-million-year cycle, according to a new study by geologist Michael Rampino of New York University.
Rampino re-examined 89 significant geological events over the past 260 million years, utilizing current age data and statistical methods. These events encompass phenomena such as marine mass extinctions, oxygen depletion in oceans, extensive volcanic eruptions, sea level fluctuations, and changes in seafloor spreading rates. His analysis suggests a primary cycle of approximately 27 million years connects these disparate events, alongside shorter and longer patterns.
The concept of geological upheavals following a regular pattern has been a subject of debate since the 1980s, with many geologists questioning the existence of a single mechanism that could link such varied occurrences. However, Rampino maintains that a deeper underlying pattern connects mass extinction events.
"While these ideas are still mostly outside the mainstream of current geological thinking, they could be the first steps in an important conceptual breakthrough in the Earth sciences," Rampino stated in his paper, published in the journal Evolving Earth. The study also identified shorter cycles of about 8.9 million years and longer ones up to 270 million years.
Potential explanations for these cycles involve shifts deep within the Earth's mantle. Periodic changes in the slow convection currents of the mantle could trigger increased volcanic activity, plate tectonics, and other large-scale geological processes. These internal changes might then have cascading effects on the oceans, climate, and biosphere. Rampino noted that the ages of continental flood basalts, evidence of massive volcanic eruptions, align with the 27-million-year cycle and coincide with two major mass extinction events.
Another hypothesis suggests that long-term variations in Earth's orbit could alter the distribution of ice, water, and sediments, subtly influencing stresses in the Earth's crust and consequently volcanic and tectonic activity over millions of years. However, direct evidence for either of these mechanisms is currently lacking.
A more intriguing explanation posits that Earth's movements within the Milky Way galaxy are responsible. As the solar system oscillates up and down across the galactic plane, crossing it approximately every 30 million years, it may trigger significant geological events. During these crossings, the gravitational influence of nearby stars could disturb comets in the distant Oort cloud, increasing the likelihood of asteroid impacts. Alternatively, passage through the dense galactic center could lead to the accumulation of dark matter in Earth's core, causing a massive release of heat through annihilation that could trigger widespread geological activity.
Rampino's research indicates that nine of the 13 known mass extinction events occurred within 0.3 to six million years of the solar system crossing the galactic plane. Given that Earth last crossed this plane three to four million years ago, the study suggests another major geological upheaval could be due within the next two million years.
Rampino acknowledges that this galactic mechanism is highly controversial and lacks substantial supporting evidence. He also noted that these findings challenge conventional interpretations of the geological record, which have generally discounted the existence of regular, multi-million-year cycles in Earth's history.
The study's findings are particularly relevant in light of the Cretaceous-Tertiary extinction event approximately 66 million years ago, which led to the demise of the dinosaurs. While climate change was a previous theory, the discovery of iridium—an element abundant in space—and the Chicxulub Crater in Mexico, dating to the same period, solidified the scientific consensus that a massive asteroid impact was the likely cause. Such an impact would have caused widespread seismic activity and global ash plumes, making survival difficult for many species.
