Our Planet Has A 27.5-Million-Year 'heartbeat', But No One Knows What Causes It

Since the dinosaurs lived 260 million years ago, Pangea splintered into the continents and islands that we know today, and mankind has quickly and irreversibly impacted the world around us.

But through all of that, it seems Earth has been keeping time. A recent study of ancient geological events suggests that our planet has a slow, steady 'heartbeat' of geological activity every 27 million years or so.

A series of clustered geological events - volcanic activity, mass extinctions, plate reorganizations, and sea level rise - is incredibly slow, a 27.5-million-year cycle of catastrophic events. However, the research team has noted that we have another 20 million years before the next 'pulse' occurs.

"Many geologists believe geological events are random over time," said Michael Rampino, a geologist at New York University and the study's lead author, in a statement in 2021.

"But our study provides statistical evidence for a common cycle, suggesting that these geologic events are correlated and not random."

89 geological events dating back 260 million years were analyzed by the team.

As you can see from the graph below, some of those times were tough – with over eight of such world-changing events clustering together over geologically small timespans, forming the catastrophic 'pulse'.

"These events include times of marine and non-marine extinctions, major ocean-anoxic events, continental flood-basalt eruptions, sea-level fluctuations, global pulses of intraplate magmatism, and times of changes in seafloor-spreading rates and plate reorganizations," the team wrote in their paper.

"Our results suggest that global geologic events are generally correlated, and seem to come in pulses with an underlying ~27.5-million-year cycle."

The geological cycle has been studied by geologists for quite some time. During the 1920s and 30s, scientists of the time suggested that the geological record follows a 30-million-year cycle, but in the 1980s and 1990s, researchers used the best-dated geological events to estimate that the time between 'pulses' was 26.2 to 30.6 million years.

The calculations now seem to be accurate - 27.5 million years is right in line with what we would expect. A study published by the same authors in late 2020 suggests that mass extinctions also occur at this 27.5-million-year mark.

"This paper is quite good, but actually I think a better paper on this phenomenon was [a 2018 paper by] Muller and Dutkiewicz," tectonic geologist Alan Collins from the University of Adelaide, who wasn't involved in this research, told ScienceAlert in 2021.

Two researchers at the University of Sydney studied Earth's carbon cycle and plate tectonics in their 2018 paper, which concluded that the cycle lasts approximately 26 million years.

In this study, Collins said many of the events examined are causal - i.e. they directly cause one another. Thus, some of the 89 events examined in this study are linked, such as anoxic events leading to marine extinctions. 

"Having said this," he added, "this 26-30 million year cyclicity does seem to be real and over a longer period of time – it also is not clear what is the underlying cause of it!"

Other research by Rampino and his team suggests that comet strikes may be responsible, and one researcher even speculates that Planet X is responsible.

Nevertheless, if Earth really has a geologic heartbeat, it may be due to something closer to home.

"These cyclic pulses of tectonics and climate change may be the result of geophysical processes related to the dynamics of plate tectonics and mantle plumes, or might alternatively be paced by astronomical cycles associated with the Earth's motions in the Solar System and the Galaxy," the team writes in their study.