Asteroid traces in Japan may be linked to dinosaur extinction

The discovery of a layer in the eastern part of Hokkaido is the first-ever confirmation of such traces in Japan, according to the recent announcement from the team, led by researchers from Tohoku University, the University of Tokyo and Fukui Prefectural University.

The asteroid, which was 10-15 kilometers in diameter, hit an area near the present-day Yucatan Peninsula, Mexico, and is considered to have been one of the causes of the extinction of dinosaurs by triggering rapid global cooling.

The traces of the asteroid impact have been found globally in strata with a high concentration of platinum group elements, which were abundant in the asteroid, known as the Cretaceous-Paleogene (K-Pg) boundary.

Tohoku University professor Reishi Takashima and others have spent 10 years studying the Nemuro Group, a set of sedimentary layers in the Hokkaido town of Urahoro that were once the seabed during the Cretaceous period.

In mudstone layers, the researchers found a layer where the concentration of platinum group elements was distinctively higher.

Through the analysis of microscopic fossils contained in the upper and lower layers and the analysis of volcanic ash dating, the layer was confirmed to be almost identical to the K-Pg boundary of some 66 million years ago.

Meanwhile, their study also suggested that the newly discovered layer has a partial stratigraphic gap and that the missing interval is estimated to be approximately 30,000 years following the impact.

The team is poised to conduct further analysis, hoping to discover uninterrupted layers corresponding to the exact timing of the asteroid impact.

"There are limited records of consecutive layers, leaving many unanswered questions about environmental changes around the period of the dinosaur extinction," Takashima said.

"Future analysis is expected to reveal the processes through which dinosaurs became extinct, and then how life gradually recovered and spread," the professor said.