Mar 26, 2019
HIROSHIMA - Japanese researchers said Monday they have found the country's oldest known rock dating back 2.5 billion years in the western prefecture of Shimane, around 500 million years earlier than the previous oldest discovery.
The Hiroshima University team collected fragments of the rock located near a forest road in the town of Tsuwano. The granite-gneiss metamorphic rock, formed by intense heat, has a striped appearance.
Many rocks of the same age exist in North Korea and northeastern China, and analysis of the latest specimen is likely to provide insight into the formation of the Japanese archipelago, which was originally connected to the Asian continent.
"We will study the chemical composition of the rock and make clear from which part of the continent it came," said Yasutaka Hayasaka, an associate professor at Hiroshima University.
The previous oldest rock in Japan consists of 2 billion-year-old gneiss found in Hichiso, Gifu Prefecture, in 1970.
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