London, March 24 : A new study has discovered that some coral colonies can "live" for more than 4000 years, as old as the pyramids, smashing the previous lifespan estimates of 70 years, and showing that the animals grow far more slowly than was thought.

It is this extremely slow growth that is the secret of the corals' long life, Brendan Roark, at Texas A and M University, told New Scientist.

Whilst other studies had estimated their age at a few hundred years at most, Roark argues that what had been considered "annual" growth rings actually take much longer to form.

The polyps that form coral are able to create massive reefs of the mineral calcium carbonate (CaCO3) over long time periods by adding successive thin layers to the base of the "cups" in which they live.

Using high-resolution radiocarbon dating, his team first studied Hawaiian corals for traces of "bomb-carbon" - a radioactive carbon isotope produced during nuclear tests in the 1950s.

They found it only in wafer-thin (10-micrometre) layers on the outermost part of corals' skeleton. This suggests that even these tiny accretions took decades to build up.

Further carbon-dating measurements from layers deep inside the corals then revealed the oldest Gerardia samples to be 2742 years old, while the Leiopathes had been growing for a whopping 4265 years.

This doesn't mean that the individual animals that secrete the coral themselves live for so long, just that the hollow "skeletons" they grow.

"On a human timescale, there is no sustainable harvest of these animals," said Roark. "We know next to nothing about how they spawn, settle and regenerate, but I have seen very few younger and smaller colonies, so even slow regeneration might not be a very likely option," he added.

Roark also hopes that preserving the coral could be useful for humans.

"Given their slow growth, we may be able to use them as high-resolution records of past climate change," he said. (ANI)