Diatoms are a major group of algae found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth’s biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, […] and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile (800 m) deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara.

~ From https://en.wikipedia.org/wiki/Diatom

I had grasped long ago that diatoms where single-cellular plants. But somehow I missed the, “with shells,” bit. Diatomaceous earth suddenly makes sense. I had always pictured the microscopic little individual diatoms that I’d seen in books; various shapes and sizes, floating in water. But I hadn’t imagined the shapes, structures and types of shells they’re building out of silicon! Turns out, people interested in nanotechnology are particularly interested in diatoms. Wonders never cease.