Photo/Illutration Minami-Torishima island in the Ogasawara island chain is located about 1,860 kilometers southeast of Tokyo. (Asahi Shimbun file photo)

A mass extinction event 11.6 million years ago was apparently due to a huge meteor impact in the Pacific Ocean off the coast of Minami-Torishima island 1,860 kilometers southeast of Tokyo in the Ogasawara island chain, say researchers.

They said they uncovered evidence of the impact in deep-sea sediment. It was already known that a mass extinction occurred about the same time, and the latest finding suggests a meteorite was responsible, the researchers said.

The team led by Tatsuo Nozaki, deputy group leader at the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), published its findings online Nov. 20 in the British journal Scientific Reports.

The researchers studied the off-island area to discover how clay sediment containing rare earth elements formed.

In geological stratum dating to 11 million years ago at a depth of 5,600 meters, the researchers found osmium, a precious metal, in high concentrations. They also found iridium and other elements.

After calculating the ratio of isotope and other factors, the researchers concluded they were extraterrestrial in origin and fell to Earth in a meteorite impact.

Mass extinctions have occurred many times in Earth’s history.

The five biggest extinctions known as the “Big Five” include the one that wiped out dinosaurs and nearly all other life about 65 million years ago.

The mass extinction 11.6 million years ago is not included in the Big Five, but is one of 11 that have occurred in the past 300 million years.

The precise cause of that mass extinction was not understood, but the latest finding suggests a meteorite was responsible.

The researchers said an impact crater on land from this ancient time had not been found, so it was reasonable to conclude the meteorite plummeted into the sea.

To view the published research results, see (https://www.nature.com/articles/s41598-019-52709-1).