Great Barrier Reef

The Great Barrier Reef, off the coast of Queensland, Australia, is the largest coral reef system on Earth, stretching more than 2,300 kilometers and made up of roughly 2,900 individual reefs. Geologically it is a biogenic carbonate structure: colonial coral polyps secrete skeletons of calcium carbonate that accumulate layer upon layer, as older material is built over by new growth, into a thick body of reef limestone along the edge of Australia's continental shelf. The reef in its present form has developed mostly over roughly the last 20,000 years, as sea level rose after the last glacial maximum and flooded the continental shelf, creating conditions for coral growth to re-establish itself; drilling cores through the reef show that similar reef structures have repeatedly grown, drowned as sea level rose too fast to keep pace, and regrown atop older reef platforms through multiple glacial cycles reaching back several hundred thousand years. Its growth and repeated collapse have therefore been tightly controlled by the same sea-level swings that accompany Earth's glacial cycles. This entity documents the Great Barrier Reef specifically as a named geological formation, its layered limestone structure, a distinct facet from Nature atlas treatment of the living reef ecosystem and from its treatment as a place in the Geography Atlas.