The 36 million year cycle

Every time that time frame is reached, something happens. For example, marine life multiplies with the appearance of new species. The indirect cause is tectonic movement. This is what generates the 36-million-year cycle. An in-depth analysis of fossil and geological records reveals this. There is a change in sea level that occurs in response to a 36-million-year cycle of tectonic movement.

The team is led by geologist Slah Boulila of Sorbonne University (France). He found that this alters several ecosystems, causing many species to disappear and new ones to flourish. These occupy the new ecological niches that emerge.

Changes in the seafloor

“In terms of tectonics, the 36-million-year cycle marks alterations between faster and slower seafloor expansion. It causes cyclic depth changes in ocean basins. And in the tectonic transfer of water to the deep Earth.” Geoscientist Dietmar Müller of the University of Sydney explains.

“These, in turn, caused fluctuations in the flooding and drying of the continents. There are periods of extensive shallow seas that fostered biodiversity.”

The Earth’s crust is never still. It is made up of separate tectonic plates that are constantly moving and recycling. Places where tectonic plates lie beneath the ocean are known as subduction zones. There, water is sucked into the depths of the mantle. It will then be spat out later through volcanic activity. This causes sea level variations over long periods of time.

Coincident cycles

In their data and simulations, the researchers found a 36-million-year cycle in the diversity of marine life. It coincided with a cycle found in tectonic and sea-level data. This is compelling evidence that sea-level changes are key to biodiversity cycles. “This research challenges previous ideas about why species have changed over long periods,” says Müller.