Geography

Hinchinbrook Island

The Great Barrier Reef is one of Australia's World Heritage Areas and one of the natural wonders of the world.

It stretches 2300km from just south of the Tropic of Capricorn between Gladstone and Bundaberg to the Torres Strait near the coast of Papua New Guinea.

It is the most extensive reef system in the world and was built entirely by living organisms. It is possibly the only structure built by living organisms [other than humans] that is visible from the moon.

At its southern end, the reef is about 300km from the mainland and rather fragmented, while at the northern end it is continuous for long stretches and up to 80km wide.

The age of the Reef

The lagoon between the outer reef and the coast is dotted with smaller reefs, cays and islands.

Drilling indicates that the coral rock that forms the base for the modern Reef is between 20m and 500m thick in places, and mostly about two million years old - although in some northern parts, the reef's foundations date back more than 18 million years.

Most of today's living corals are much younger, and have developed within the past 18,000 years since the end of the last Ice Age. Many of the places that support reefs today were part of the land during the Ice Age.

As global temperatures increased, and the ice melted and retreated to the poles and mountain tops, sea levels rose to their present levels, creating ideal conditions for corals to develop along the tops of what were formerly low coastal hills.

The Great Barrier Reef comprises about 2900 separate reefs off the coasts of the islands and the mainland, and barrier reefs facing the sea. The outer reef lies along the edge of the Australian continental shelf.