Opal coral reef off Cairns Great Barrier Reef, Australia.
Photograph by David Doubilet, National Geographic Creative
The iconic white cliffs of Dover are made of chalk, a graveyard made of coccoliths—the calcite plates that sheath some single-celled organisms.
Photograph by Dean Conger, National Geographic Creative
The roots of mangrove trees provide refuge for a dazzling array of marine organisms—and can even anchor the formation of small islands.
Photograph by Tim Lamán, National Geographic Creative
Termites build large mounds over their underground colonies to help provide ventilation and climate control.
Photograph by Jason Edwards, National Geographic Creative
As they eat algae, parrotfish grind up coral and poo out fine-grained sediment that builds up on beaches as sand.
Photograph by David Doubilet, National Geographic Creative
Some of the oldest fossils of life on Earth are stromatolites: mineral structures formed by mats of photosynthetic microbes.
Photograph by Michael and Patricia Fogden, National Geographic Creative
