A new study published in Science suggests that most sharks and shark species died out during a mass extinction 1
Researchers Elizabeth Sibert and Leah D. Rubin have found evidence of the mass extinction in ancient sediment core samples taken from the waters of the South Pacific and North Pacific. The samples, which contain materials that are hundreds of millions of years old, were collected in 1983 and 1992 by the International Ocean Discovery Program. Apparently, the thousands of shark scales in these samples were overlooked until recently.
Shark scales, or denticles, are a good indicator of how many sharks there were in an area at a given time. In that regard, the core samples from the North and South Pacific tell an interesting story: Earth’s waters contained a dizzying array of sharks until 19 million years ago, when shark populations abruptly declined by 90%. Even more disturbing is that about 70% of shark species are now extinct.
But researchers can’t figure out why the sharks died so suddenly. Common suspects, such as water temperature and carbon cycling, appear to have been stable when the extinction occurred. It looks like the mystery won’t be solved until we have more data.
Unfortunately, we don’t have much data from 19 million years ago. Scientists need to collect more core sediment samples to see if something unusual caused the mass extinction. As noted by Elizabeth Sibert and Leah D. Rubin, researchers haven’t had a chance to analyze core samples from the Atlantic, so it’s possible that this mass extinction only happened in the Pacific (although this is unlikely, as oceanic changes happen). mostly on a global scale).
As we continue to study the distant past, we are guaranteed to discover more mass extinction events. The impact these events have on Earth’s history and the present may be impossible to know, but at least we can try to figure out what led to them in the first place.
Source: Science via Ars Technica