Japan's oldest known human remains have been found in cave remains on Ishigaki Island in Okinawa Prefecture, a researcher has announced. Minoru Yoneda, associate professor at the University of Tokyo, confirmed the human remains dating back some 24,000 years after inspecting human bones excavated at the Shirahosaonetabaru cave remains in the city of Ishigaki, Okinawa Prefecture.
     The ancient cave is also home to approximately 20,000-year-old human remains dating back to the Paleolithic Period - previously the nation's oldest known traces of human existence. A past survey had found that one of the six pieces of human bones found at the site dated back some 20,000 years through direct measurement of radioactive carbon of collagen extracted from those bones. However, researchers had been unable to identify the geological layer that hosted the human remains.
     Yoneda analyzed some 25 pieces of human bones that were freshly excavated from the 20,000 to 24,000-year-old bottom layer and other locations at the cave remains before 2010. By using radiocarbon dating, one of the rib bone pieces excavated from the bottom layer has turned out to be about 24,000 years old, while three other bone fragments proved to be some 20,000 years old.
     On mainland Japan, which has abundant acid soil, human remains found in Hamakita (present-day Hamamatsu), Shizuoka Prefecture -- which have been confirmed to date back some 18,000 years through the use of radiocarbon dating -- are the only known human bones from the Paleolithic Period.

Edited from The Mainichi Daily News (10 November 2011), Japan Update (2 December 2011)