Ancient Stromatolite ReefsMicrobe-rich stromatolite reefs, like this one in Shark Bay, Australia, were among the first sources of oxygen on Earth. They flourished throughout the planet's shallow waters 3.5 billion years ago, but are extremely rare today.

Photograph by O. Louis Mazzatenta

PHOTO GALLERY

Oceans

Dive into one of the most magnificent habitats on Earth.

October 9, 2009

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