Most of the modern Great Barrier Reef’s development belongs to the Holocene epoch. The Holocene began about 11,700 years ago, after the end of the last major ice age.
As glaciers melted, sea level rose and flooded parts of the continental shelf along northeastern Australia. Coral communities colonised suitable shallow areas and gradually built reef structures upward and outward. Earlier reef generations existed during previous periods, but many were drowned, buried or altered as sea levels changed.
The Holocene reef is therefore geologically young even though corals have existed for hundreds of millions of years. The Great Barrier Reef is not a single structure that has remained unchanged since the age of dinosaurs. It is a changing sequence of reef communities shaped by sea-level fluctuations, sediment, storms and coral growth.