The evolution of life on Earth has changed dramatically at tens of million-year time scales. However, the causal mechanisms of these changes remain unclear. In new research, scientists from Sorbonne Université, the University of Madison, the University of Sydney and the Université de Genève found evidence for 36-million-year cycles in marine animal fossil data over the last 250 million years. The authors also found similar, correlatable cycles in sea-level and Earth’s interior processes, suggesting that long-term marine biodiversity was paced by geodynamically driven global sea-level cycles.
Marine and land life evolves dramatically at tens of million-year time scales.
One measure of the changes in evolutionary tempo is the fluctuation in biodiversity, such as the well-documented fossil data on marine animal families and genera.
The biodiversity data are punctuated by five severe mass extinction events, or biotic crises, caused by various mechanisms.
Numerous studies have argued for or against the cyclic nature of biodiversity variations at tens of million-year time scales, but the inferred causes for the cyclic variations from external and/or Earth’s internal processes have remained conjectural.
“In terms of tectonics, the 36-million-year cycle marks alterations between faster and slower seafloor spreading, leading to cyclical depth changes in ocean basins and in the tectonic transfer of water into the deep Earth,” said University of Sydney’s Professor Dietmar Müller.
“These in turn have led to fluctuations in the flooding and drying up of continents, with periods of extensive shallow seas fostering biodiversity.”
Professor Müller and colleagues based their findings on the discovery of strikingly similar cycles in sea-level variations, Earth’s interior mechanisms and marine fossil records.
They now have overwhelming evidence that tectonic cycles and global sea level change driven by Earth’s dynamics have played a crucial role in…
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