A new study published in Science suggests that most sharks and shark species died off in a mass extinction event 19 million years ago. It may have been the most devastating extinction event in sharks’ 450 million-year history, but scientists can’t explain what went wrong.
Researchers Elizabeth Sibert and Leah D. Rubin found evidence of the mass extinction event in ancient sediment core samples taken from the South Pacific and North Pacific waters. The samples, which contain materials dating back hundreds of millions of years, were collected in 1983 and 1992 by the International Ocean Discovery Program. Evidently, the thousands of shark scales contained in these samples were overlooked until recently.
Shark scales, or denticles, are a good indicator of how many sharks were in an area during a certain period. In that regard, the North and South Pacific core samples tell an interesting story—the Earth’s waters held a dizzying array of sharks until 19 million years ago, when the shark population abruptly declined by 90%. Even more troubling, about 70% of shark species went extinct at this time.
But researchers can’t figure out why the sharks died off so suddenly. Usual suspects, such as water temperature and carbon cycles, appear to have been stable when the extinction event occurred. The mystery, it seems, won’t be solved until we have more data.
Unfortunately, we don’t have a lot of data from 19 million years ago. Scientists need to collect more core sediment samples to see if anything unusual caused the mass extinction event. As noted by Elizabeth Sibert and Leah D. Rubin, researchers haven’t had the chance to analyze core samples from the Atlantic ocean, so it’s possible that this mass extinction event occurred only in the Pacific ocean (though this is unlikely, as oceanic changes tend to happen on a global scale).
As we continue to study the distant past, we are guaranteed to discover more mass extinction events. The impact that these events have on Earth’s history and the present day may be impossible to know, but at least we can try to figure out what led to them in the first place.