For decades the Chinese mined a phosphorus-rich layer of rock that winds through the hillsides of Guizhou Province and used it to make fertilizer for rice paddies. Then, in the 1980s, several geologists noticed fossils embedded in that layer, which they called the Doushantuo Formation. Viewed under a microscope, the fossils were exquisite—spherical and segmented on their surface, like a blackberry. Most people believed they were ancient algae.