A research group at the University of Tokyo and their collaborators have demonstrated for the first time that an impact with a large meteorite was responsible for the mass extinction of marine organisms during the late Triassic period nearly 215 million years ago. In 2013, evidence of an impact dating back 215 million years involving a meteorite 3.3-7.8 km in diameter was discovered in a claystone layer embedded in exposed chert rock along the Kisogawa River in the town of Sakahogi, Gifu Prefecture, in central Japan. However, the effects of the impact on Earth’s environment, including whether it had led to the extinction of marine life inhabiting the oceans at the time, was unknown.
The research group of Professor Yasuhiro Kato at the Frontier Research Center for Energy and Resources, Graduate School of Engineering, the University of Tokyo, and their collaborators investigated the extinction patterns of marine organisms by studying the fossils of radiolarians and conodonts found in the late-Triassic chert in Sakahogi, as well as analyzing the chemical composition of the chert layer. The researchers found that: (1) a large number of radiolarians and conodonts became extinct in the period immediately following the impact; (2) production of phytoplankton dropped significantly for tens of thousands of years after the impact, and the number of radiolarians also decreased during the same period; and (3) new species of radiolarians that did not exist before the impact emerged after production of phytoplankton was restored, eventually replacing older species and driving them into extinction.
Prior to this study, the findings from a 66 million-year-old sedimentary layer that helped establish the now-famous theory of the meteorite impact that caused the extinction of dinosaurs provided the only strong evidence of a meteorite impact setting off a mass extinction. The current research has shown for the first time that another impact event, which occurred 215 million years ago—long before the one that triggered the extinction of dinosaurs—brought about the collapse of the marine ecosystem at the time. The research group aims to expand its study to evaluate the effects of the impact on other life forms inhabiting the Earth at the time, including mammal-like reptiles, dinosaurs, and other land organisms. The researchers further plan to examine the effects of the impact on the Earth’s environment, such as global cooling and acid rain.
“This epoch-making discovery presented the only other evidence of a mass extinction caused by a large meteorite impact besides that for the event at the end of the Cretaceous period that is now well known for wiping out the dinosaurs,” says Kato. He continues, “Revealing how a mass extinction occurred in the past provides us with important clues for predicting the influence of future environmental changes on the Earth’s ecosystems.”
This research was carried out in collaboration with Associate Professor Tetsuji Onoue at the Department of Earth and Environmental Sciences at Kumamoto University, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kochi University, Niigata University, and Chiba Institute of Technology.
Source: University of Tokyo