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Early Life

These rocky formations, called stromatolites, are made by photosynthetic cyanobacteria and other microorganisms. The microbes secrete compounds that bind sediment grains, creating a fine-layered mineral “microfabric.” Stromatolites were among the earliest life on Earth, and massive formations dominated shorelines starting about 3.5 billion years ago. About 1 billion years ago, their populations mysteriously plummeted; now they exist in only a few locations, like this one in Shark Bay, Australia. WHOI scientists Joan Bernhard and Virginia Edgcomb have investigated that decline, which occurred as more complex life forms were emerging. (Photo by Virginia Edgcomb, Woods Hole Oceanographic Institution)