Ancient mass extinctions hint at possible ocean future

 Brandon Keim -

In sediment traces and fossil records from one of Earth’s most tumultuous periods, geologists have found a narrative linking mass extinctions with planetary biological and geological change.

After dramatic oceanic extinctions 250 million and 200 million years ago, the global carbon cycle turned chaotic. Earth’s biogeochemistry went boom and bust for millions of years thereafter, as if some regulating mechanism were lost — which is exactly what happened.

“People talk about saving biodiversity, and isn’t it good to have a variety of all these creatures. But the reason it matters is because ecosystem function is itself dependent on diversity in the face of normal environmental changes,” said geologist Jessica Whiteside of Brown University. “Lower diversity too much, and the system will lose its resiliency. It will become a slave to otherwise minor environmental changes.”

Whiteside specializes in reading the geological record of past extinctions, teasing from rocks and fossils the story of those times in Earth’s history when, for one reason or another, most forms of life ceased to exist.

In the new study, published Jan. 5 in Geology, Whiteside and University of Washington biologist Peter Ward focus on two mass extinctions with especially catastrophic marine consequences: the Permian-Triassic extinction event 250 million years ago, when 96 percent of all ocean species went extinct, and the Triassic-Jurassic extinction 200 million years ago, which extinguished 20 percent of all marine families.

Scientists say that another mass extinction is now underway, with extinction rates an order of magnitude higher than normal, both on land and at sea. Studies like Whiteside’s suggest what the extinction’s consequences could be — not just for people, on a scale of decades or centuries, but for how the planet will work, millions of years in the future.

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