Geological History and Marine Life Diversity

The Great Barrier Reef has a complex geological history. Although the underlying basement of the reef is 18 million years old in the north and two million years old in the south, the reefs and cays we see today are less than about  15,000 years old.

65 million years ago
The Australian Continent broke away from a large land mass called Gondwanaland, which was located in cold southern water.

18,000 years ago
The last Ice Age began. Sea level dropped 100 m as the water became frozen in ice caps. All reefs on the continental shelf were exposed. They became hills covered with vegetation.

About 15,000 years ago
The Ice Age ended. Ice caps thawed and sea level rose 100m (300 feet). As the ocean flooded the continental shelf, coral reefs reformed on the old reef structures.