The Reef Research Centre has found the remains of coral that are half a million years old.
Corals have been growing in the region for as long as 25 million years.
The corals have not always formed coral reefs.

It is difficult to work out the age of the Great Barrier Reef.
This is because of the way a reef can grow and shrink as the sea level changes.
A coral reef can grow in diameter, that is how wide they are, from 1 to 2 cm per year.
They can also grow upwards from 1 to 15 cm per year.
Coral can not grow if the water is too deep (150 metres or more) because it needs light from the sun.
They cannot grow out of the water (above sea level).

The Great Barrier Reef Marine Park Authority and Australian Institute of Marine Science say the current, living reef started growing about 20,000 years ago.
It started to grow on an older reef.
This makes the beginning of  the reef duringay.
The land that forms the bottom of the Great Barrier Reef was a coastal plain.
The plain had some large hills.
Some of these hills were parts of older reefs.

From 20,000 years ago until 6,000 years  the sea level began to rise.
As it rose, the corals could grow higher on the hills of the coastal plain.
13,000 years ago the sea level was 60 metres lower than the present day.
Corals began to grow around the hills of the coastal plain.
These became continental islands.
As the sea level rose higher, most of these continental islands were covered by water.
The corals could then grow over the hills.
This formed the present cays and reefs.
Sea level on the Great Barrier Reef has not risen much in the last 6,000 years.
The CRC Reef Research Centre has worked out that the present, living reef is 6,000 to 8,000 years old.

The remains of a very old barrier reef has been found in the Kimberley area.
This is in the northern part of Western Australia.

The Great Barrier Reef World Heritage Area has been divided into 70 different areas.
These are called bioregions.
Each bioregion has its own special plants and animals.
There are 30 reef bioregions, and 40 are non-reef bioregions.
 In the northern part of the Great Barrier Reef, there are ribbon reefs and deltaic reefs.
These kinds of reef do not exist in the rest of the Great Barrier Reef system.
The Reef Research Centre has found the remains of coral that are half a million years old. Corals have been growing in the region for as long as 25 million years. The corals have not always formed coral reefs.
It is difficult to work out the age of the Great Barrier Reef. This is because of the way a reef can grow and shrink as the sea level changes. A coral reef can grow in diameter, that is how wide they are, from 1 to 2 cm per year. They can also grow upwards from 1 to 15 cm per year. Coral can not grow if the water is too deep (150 metres or more) because it needs light from the sun. They cannot grow out of the water (above sea level).
The Great Barrier Reef Marine Park Authority and Australian Institute of Marine Science say the current, living reef started growing about 20,000 years ago. It started to grow on an older reef. This makes the beginning of  the reef duringay. The land that forms the bottom of the Great Barrier Reef was a coastal plain. The plain had some large hills. Some of these hills were parts of older reefs.
From 20,000 years ago until 6,000 years  the sea level began to rise. As it rose, the corals could grow higher on the hills of the coastal plain. 13,000 years ago the sea level was 60 metres lower than the present day. Corals began to grow around the hills of the coastal plain. These became continental islands. As the sea level rose higher, most of these continental islands were covered by water. The corals could then grow over the hills. This formed the present cays and reefs. Sea level on the Great Barrier Reef has not risen much in the last 6,000 years. The CRC Reef Research Centre has worked out that the present, living reef is 6,000 to 8,000 years old.
The remains of a very old barrier reef has been found in the Kimberley area. This is in the northern part of Western Australia.
The Great Barrier Reef World Heritage Area has been divided into 70 different areas. These are called bioregions. Each bioregion has its own special plants and animals. There are 30 reef bioregions, and 40 are non-reef bioregions.  In the northern part of the Great Barrier Reef, there are ribbon reefs and deltaic reefs. These kinds of reef do not exist in the rest of the Great Barrier Reef system.
Great Barrier Reef