After Earth’s temperatures spiked and oxygen levels in the sea plummeted some 252 million decades back, most life in the world was doomed. Some estimates indicate the extinction event, a mass extinction called the Great Dying, murdered off around 70 percent of land species however marine creatures felt that the effect even greater. As much as 96 percent of all species from the planet’s oceans expired.

But maybe not sharks. The slim prowlers of this deep persevered. “They are the greatest survivors,” states Elizabeth Sibert, a paleobiologist and oceanographer in Yale University.

The longevity of sharks is mythical however they’ve come much closer to extinction than we believed, according to another study, printed in the journal Science on Thursday. The study, headed by Sibert, reveals a formerly unknown extinction occasion pushed sharks into the verge 19 million decades back, leaving only about one in 10 whales from the open sea living.

“Something happened that pumped out 90 percent of these ” Sibert states. That which something was remains unclear, but it was certainly catastrophic.

It ended up being a small surprise, involving a deep-sea detective work along with a mountain of microfossils.

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Buried treasure
Every time a marine creature dies, its stays descend into the abyss, decomposing from entire creature to constituent components. Tiny bits of the fallen, such as the scales found on a shark (denticles) and teeth out of fish down rain upon the sea floor and, as time passes, pile up from the sediment.

“The ocean floor is basically a graveyard for all of the life that’s living anywhere in the water column,” says Sibert.

Each denticle or tooth is like a tiny headstone. As they’re embedded into the sediment, they leave a fossilized record of life. These fossils are known as “icthyoliths.” And denticles don’t just get subsumed by the sediment when a shark dies either. “They shed their denticles throughout their whole life,” notes Rubin. “That makes them a really abundant fossil.”

Extracting a cylindrical core of sediment allows scientists to analyze the types of icthyoliths embedded within — giving them a good proxy for what the ocean ecosystem looked like across deep time. The deeper you dig, the further back in time you can travel.

The sediment cores used in the study come from two locations in the Pacific Ocean, one northern and one southern site, and cover a timescale of 40 million years. They were gathered from about 3.5 miles below the surface by the JOIDES Resolution, a research vessel that can drill into the seafloor.