SCIENCE: Earth Has a 27.5‑Million-Year ‘Heartbeat’, But We Have No Idea What Causes It

In the last 260 mil­lion years, dinosaurs came and went, Pangea split into the con­ti­nents and islands we see today, and humans have quick­ly and irre­versibly changed the world we live in.

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.

This pulse of clus­tered geo­log­i­cal events – includ­ing vol­canic activ­i­ty, mass extinc­tions, plate reor­ga­ni­za­tions, and sea lev­el ris­es – is incred­i­bly slow, a 27.5‑million-year cycle of cat­a­stroph­ic ebbs and flows. But luck­i­ly for us, the research team notes we have anoth­er 20 mil­lion years before the next ‘pulse’.

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

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

The team con­duct­ed an analy­sis on the ages of 89 well-under­stood geo­log­i­cal events from the past 260 mil­lion years.

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.”

Geol­o­gists have been inves­ti­gat­ing a poten­tial cycle in geo­log­i­cal events for a long time. Back in the 1920s and 30s, sci­en­tists of the era had sug­gest­ed that the geo­log­i­cal record had a 30-mil­lion-year cycle, while in the 1980s and 90s researchers used the best-dat­ed geo­log­i­cal events at the time to give them a range of the length between ‘puls­es’ of 26.2 to 30.6 mil­lion years.

Now, every­thing seems to be in order – 27.5 mil­lion years is right about where we’d expect. A study pub­lished in late 2020 by the same authors sug­gest­ed that this 27.5‑million-year mark is when mass extinc­tions hap­pen, too.

“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.

That 2018 paper, by two researchers at the Uni­ver­si­ty of Syd­ney, looked at Earth­’s car­bon cycle and plate tec­ton­ics, and also came to the con­clu­sion that the cycle is approx­i­mate­ly 26 mil­lion years long.

Collins explained that in this lat­est study, many of the events the team looked at are causal – mean­ing that one direct­ly caus­es the oth­er, thus some of the 89 events are relat­ed: for exam­ple, anox­ic events caus­ing marine extinction.

“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 from Rampino and his team have sug­gest­ed comet strikes could be the cause, with one space researcher even sug­gest­ing Plan­et X is to blame.

But if Earth real­ly does have a geo­log­ic ‘heart­beat’, it might be due to some­thing a lit­tle 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.

The research has been pub­lished in Geo­science Frontiers.

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