Geohistory - Rocks from Continental to Sea Periods
Around 15–10 million years ago, after the formation of the Sea of Japan, the land of the Oki Islands was part of the seabed. Sediments formed at that time can now be seen on the land. Among these sediments, diatomaceous earth is particularly characteristic. This rock is made up of fossils of diatoms, a type of plankton covered in a glassy shell, seen in almost every water environment on Earth. Once diatoms die, their shells fall to the bottom of the sea and eventually create diatomaceous earth. Since diatom shells are porous, diatomaceous earth is light and does not conduct heat well. It is thus often used in heat-resistant bricks and shichirin charcoal grills. Diatomaceous earth is found in the southwestern part of Dōgo Island, where it was mined for use in construction.
