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Gift of Japan's oldest rock to Gifu Pref. museum shows solid bond between two towns

Japan's oldest known rock discovered in Tsuwano, Shimane Prefecture, front, and the second oldest rock found in the town of Hichiso, Gifu Prefecture, rear, are seen side by side in the "Japan's oldest rock museum" in Hichiso, Gifu Prefecture, on July 22, 2020. (Mainichi/Yoji Hanaoka)

A town in western Japan gifted a chunk of the country's oldest primordial rock to a municipal museum in central Japan as a token of friendship after the former supplanted the latter as home to the archipelago's most ancient known boulder.

    The current titleholder boulder was found in the town of Tsuwano, Shimane Prefecture, western Japan by a team of researchers at Hiroshima University in May 2017, and research results released in March 2019 revealed it to be granite-gneiss clocking in at around 2.5 billion years old. That beat out a granite-gneiss rock dating back some 2.05 billion years discovered in 1970 in the Hisuikyo ravine near the Hida River, in the town of Hichiso, Gifu Prefecture, central Japan.

    Hichiso had promoted itself as the discovery spot for the oldest rock of the country, and even erected a "Japan's oldest rock museum" in 1996 near the ravine to exhibit it, as well as Earth's most elderly known stone found in Canada and dated to 4.03 billion years ago. The ravine itself is also a popular tourist attraction. The Tsuwano rock revelation put Hichiso in a hard spot.

    Tsuwano, however, came to the rescue, presenting Hichiso with an 18-kilogram hunk of the now-oldest rock. Hichiso subsequently revamped the museum exhibit, with the Tsuwano sample as its centerpiece. A reopening ceremony is set for 9 a.m. on Aug. 2.

    Donating a part of the Tsuwano rock to the Gifu Prefecture town was the brainchild of Yasutaka Hayasaka, an associate professor at Hiroshima University who was worried about the discovery's impact on Hichiso's local revitalization efforts. The two towns actually had existing ties -- Hichiso had dispatched staff to Tsuwano to help the town recover from a torrential rain disaster in July 2013.

    The rock segment was handed over in a ceremony in Tsuwano in February this year. Hichiso Mayor Keiji Ido commented, "I was relieved that the rock was discovered in Tsuwano. We can keep the name of the museum, and the first and second oldest rocks can both be seen here. We hope that the rocks will create an everlasting bond between our towns."

    Tsuwano Mayor Hiroyuki Shitamori also commented, "We had mixed feelings when the rock was discovered, but the town of Hichiso was kind enough to be delighted at the news. I would like to deepen the interactions between our towns." The mayor spoke of his hope to start exchange visits to create opportunities for children to learn about rocks, as well as to cooperate on tourism.

    The "Japan's oldest rock museum" closed for its overhaul in February. The current and former "oldest rocks" are displayed side by side with a description reading, "The origin of the Japanese archipelago is likely to be understood better when the similarities and differences of the rocks of both (towns') regions are revealed."

    Although the museum had reopened in March, it was temporarily closed again between March and May due to the novel coronavirus, pushing back the reopening ceremony. Admission is free on the opening ceremony day of Aug. 2. The museum has also called on public suggestions for the names of a pair of mascots, and the winning entries will be announced on the same day.

    (Japanese original by Yoji Hanaoka, Gifu Bureau and Yukihiro Takeuchi, Masuda Local Bureau)

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