An ancient silica sea
The pale cliffs of the Noto Peninsula are not ordinary rock. They are a massive graveyard of microscopic algae called diatoms. This material, known as diatomaceous earth or diatomite, is a fossilized record of a colossal plankton bloom that filled the ancient Japan Sea. Geological analysis of the local strata, such as the Tsukada Formation, dates this event to the Middle Miocene epoch, between 11.6 and 12.3 million years ago.
Diatoms are single-celled organisms that construct glass-like shells, or frustules, from silica. During the Miocene, tectonic activity and volcanism associated with the formation of the Japan Sea released enormous quantities of silica into the water. This influx of nutrients triggered a sustained population explosion of diatoms. As countless generations of these organisms died, their tiny silica shells rained down on the seabed. Over millions of years, these deposits compacted to form the thick, porous rock layers visible across the peninsula today. Some of the rock formations are composed almost entirely of these microscopic fossils.
A high-fidelity fossil record
The Noto Peninsula's diatomite records a past marine ecosystem. The fine-grained nature of the sediment created an ideal medium for fossil preservation. Micropaleontologists have identified numerous diatom species within these layers, including those from the genera Denticulopsis, Coscinodiscus, and Thalassiosira. The specific assemblages, such as those of the Denticulopsis praedimorpha Zone, allow scientists to precisely date the rock and reconstruct the paleo-environment.
The bloom itself had a dramatic effect on the local ocean. The immense quantity of dying plankton sinking to the sea floor led to anoxic conditions—a lack of oxygen in the bottom waters. While detrimental to many bottom-dwelling animals, this oxygen-poor environment slowed decomposition and increased the preservation of organic material and fossils. These layers of diatomite show a period of major global cooling and heightened biological productivity in the North Pacific Ocean.
The unique geology is visible in landmarks like Mitsuke Island, a 28-meter-high rock off the coast of Suzu City composed of this same diatomaceous earth. The material is so soft that the island's shape is noticeably altered by earthquakes and erosion.
From seabed to tabletop grill
For centuries, residents of the Noto Peninsula have quarried this fossil-rich earth. Its physical properties are useful. The rock is filled with countless microscopic pores from the silica shells, which gives it low density and fantastic insulating capabilities. These qualities make it the perfect material for crafting traditional Japanese charcoal grills known as shichirin or konro.
Artisans in Suzu City carve blocks of diatomite directly from the quarry into grills. When in use, the porous material retains heat with extreme efficiency, allowing the charcoal to burn at very high temperatures while the outside of the grill remains cool enough to touch. This ancient plankton is also a component in modern life in other ways. Finely crushed diatomite is used as a strengthening undercoat for the region's famous Wajima lacquerware and as a humidity-regulating additive in plaster walls.