Changes in Earth’s orbit could explain rise and fall of ancient species

New research published in Proceedings of the National Academy of Sciences looks back 450 million years to reveal an important link between changes in our planet’s motion through space, and the extinction and evolution of life on Earth.A team of researchers, including paleontologist Michael Foote at the University of Chicago, examined the fossils of graptoloids, an extinct type of plankton that floated in ancient oceans. They found evidence that regular changes in the Earth’s orbit and axis of rotation caused significant changes in both the evolution and extinction rates of these creatures.

“This research is very exciting because the relationship between these orbital changes and extinction has never been shown before in truly ancient ecosystems,” said Prof. James Crampton of Victoria University of Wellington, who led the study. “There’s a strong debate in science about the impact on extinction and evolution of environmental change versus interactions between species (such as competition for food). With this study we can provide evidence of the impact of environmental changes on life on Earth.”

As it travels around the sun, Earth’s orbit fluctuates slightly in cycles of tens of thousands to millions of years. These cycles change the axis and tilt toward the sun, which changes the sunlight and climate on Earth. It seems likely this affected evolution on Earth, but the details remain unclear—especially further back than a few hundred thousand years.

But the fossil plankton data was so rich that they could see clear evidence of cycles. Between 9 percent and 16 percent of the variance in plankton species extinctions could be explained by such astronomical cycles, over a span of 60 million years, the study found.

“This kind of cyclicity has been difficult to document in such ancient records—that is, going back hundreds of millions of years rather than hundreds of thousands,” said Foote, a professor of geophysical sciences at the University of Chicago and a co-author on the paper.

The analysis was possible due to the extensive fossil graptoloid dataset developed by New Zealand’s GNS Science and the University of California-Riverside, researchers said. It covers the entire globe, and the average resolution in the record is about 40,000 years, rather than the multiple millions that Foote is used to dealing with. “As exciting as this result is, I’m equally excited for the potential for other studies that one could do with the fabulous level of detail in this dataset,” he said.

Citation: “Pacing of Paleozoic macroevolutionary rates by Milankovitch grand cycles,” Crampton et al, Proceedings of the National Academy of Sciences, USA May 15, 2018. DOI: 10.1073/pnas.1714342115

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