The Earth, our home, is like a steadily beating heart

27.5 million years - this is the length of the Earth's "pulse"

A study shows that in the Earth's recent history, many major geological events have occurred every 27.5 million years. This pattern covers most of the major geological events, so scientists call it the "pulse of the Earth."

Over the past 260 million years, a host of major geological events — including changes in sea level and volcanic eruptions — appear to have followed this pattern.

"For a long time, some geologists have suspected that there are cycles of about 30 million years in the geological record," said Michael Rampino, a professor in the Department of Biology and Environmental Studies at New York University and the lead author of the paper. But until now, quantitative studies of the phenomenon have been difficult to conduct because of the imprecise dating of such events.

"A lot of geologists would say that geological events happen in a fairly random way," Rampino said. But in the new study, Rampino and his team did some quantitative analysis to see if they really were random, or if there were underlying patterns.

The team first reviewed the literature and selected 89 major geological events that have occurred in the past 260 million years. These events include species extinctions, ocean anoxic events (oceans become uninhabitable due to oxygen depletion), sea level fluctuations, some major volcanic events that produced "basaltic magma floods", and changes in Earth's plate tectonics.

The researchers then put the events in chronological order and used a mathematical tool called Fourier analysis to find the years when the frequency of events peaked. They found that most of these events clustered in 10 different years, which were separated by an average of 27.5 million years. Rampino said that number may not be "exact," but it is a "pretty good estimate" with a statistical confidence level of 96%, which means it is "unlikely to be a coincidence."

The frequency of major geological events is plotted against the historical age. As can be seen from the figure, a group of major geological events occurs every 27.5 million years.

The researchers only looked at the past 260 million years—because that’s when geological events are most accurately dated—but they think the results may be generalizable to earlier periods in our planet’s history. “For example,” says Rampino, “there are data on sea level changes going back about 600 million years, and the pattern seems to hold.”

"It is not clear what causes this periodicity in geological activity, but it could be due to plate tectonics and internal motions of the mantle," the researchers wrote in their study paper. "Or it could be related to the motion of the Earth in the solar system and the Milky Way," Rampino said. "For example, according to this study, the 27.5-million-year period is close to the 32-million-year period of Earth's reciprocating motion normal to the galactic plane."

"There is a theory that the solar system sometimes passes through a plane in the Milky Way that contains a lot of dark matter. When a planet passes through the dark matter, it absorbs the dark matter," Rampino said. "These large amounts of captured dark matter can annihilate and release heat, which periodically generates heat in geological structures and triggers geological activity. This may be the cause of the so-called 'pulse of the Earth.'" However, this is just a guess. After all, scientists still don't know what dark matter is made of or how it is distributed in the solar system.

Rampino and his team hope to get better data on the ages of these geological events and plan to analyze whether the periodicity persists further into Earth's history. They also hope to one day get better astronomical data describing the motion of Earth in the solar system and the Milky Way, so they can see if there is a connection between astronomical and geological cycles.

"In any case, as long as this periodicity exists, since the last major eruption was about 7 to 10 million years ago, the next major eruption may occur in 15 to 20 million years," Rampino said.

BY: Yasemin Saplakoglu

FY: Romanticism

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