Earth has a pulse – 27.5-million-year cycle of geologic activity

Geologic activity on Earth appears to follow a 27.5-million-year cycle, giving the planet a “pulse,” according to a new study published in the journal Geoscience Frontiers.

“Many geologists believe that geological events are random in time. But our study provides statistical evidence of a common cycle, suggesting that these geologic events are interrelated, not random,” says Michael Rampino, a geologist and professor in the Department of Biology at New York University and lead author of the study.

Over the past five decades, researchers have assumed cycles of major geologic events – including volcanic activity and mass extinctions on land and at sea – lasting about 26 million to 36 million years. Early work on these relationships in the geologic record, however, was hampered by limitations in determining the age of geologic events, which prevented scientists from conducting qualitative studies.

Now, however, there have been significant improvements in radioisotope dating techniques and changes in the geologic time scale that have resulted in new data on the timing of past events. Using the latest available dating data, Rampino and colleagues collected updated data on major geologic events over the past 260 million years and conducted a new analysis.

The team analyzed the ages of 89 well-dated major geologic events over the past 260 million years. These events include extinctions of marine and terrestrial organisms, large volcanic lava outpourings called basalt eruptions, events when the oceans were depleted of oxygen, sea-level fluctuations, and changes or reorganizations of Earth’s tectonic plates.

They found that these global geologic events are generally clustered at 10 different time points over 260 million years, combined into peak periods at intervals of about 27.5 million years. The last burst of geologic events occurred about 7 million years ago, suggesting that the next burst of major geologic activity will occur more than 20 million years later.

Researchers speculate that these pulses may be the result of cycles of activity in the Earth’s interior – geophysical processes associated with plate tectonics and climate dynamics. However, similar cycles in the Earth’s orbit in space could also be responsible for these events.

“Whatever the origin of these cyclic episodes, our results support the theory that the geological record is largely periodic, coordinated and periodically catastrophic, which diverges from the views held by many geologists,” explained Rampino.

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