Within Japan, in the islands of Okinawa, are sites where many human fossils have been discovered.. This is due to the presence of large quantities of calcium carbonate, which leaches out in the substrate water in the Ryukyuan limestone caves of Okinawa. The concentration of calcium carbonate in these stalactite caves has fossilized the bones of humans that were within.
In the digs from other areas of Japan, such as sites in the Kanto region's loam, the acidic nature of the volcanic soil was not conducive to fossilization and most bones dissolved away quickly.
Surveys confirm that there are as many as 600 caves in Okinawa, but most have not been investigated and have been filled in or destroyed. It is desirable to conduct careful study in them because of the possibility of archeological finds within. It is thought that through the advances brought about by investigation and excavation of these stalactite caves, the chances are certain that an increasing number of human fossils will be found.