Image caption The discovery was made at the Giant's Causeway

In a small grey puddle tucked into a corner of the world famous Giant's Causeway, scientists have made an extraordinary find.

A colony of stromatolites - tiny structures made by primitive blue-green algae.

Stromatolites are the oldest known fossils in the world.

The tiny algae or bacteria that build them are also thought to be the most ancient life form that is still around today, after more than three billion years.

What makes the discovery in Northern Ireland so remarkable is that until now these structures have been found mainly in warm and often hyper saline waters which discourage predators.

The stromatolites in the Giant's Causeway are in a tiny brackish pool, exposed to the violence of waves and easy prey to the animals that are already living amongst them.

Stromatolites are formed by blue-green algae that excrete carbonate to form a dome-like structure. Over thousands of years these build up into a hard rock that continues to grow.

Stromatolite fossils have been dated as far back as three and a half billion years.

The colony at the Giant's Causeway on Northern Ireland's wind-swept north coast was found by accident.

Scientists from the School of Environmental Sciences at the nearby University of Ulster were looking for very different geological formations when Professor Andrew Cooper spotted the stromatolites.

'Puzzling'

"I was very surprised", explained Professor Cooper.

"I was walking along with a colleague looking at something else. Out of the corner of my eye I spotted these structures which, had I not seen them before in my work in South Africa, I probably wouldn't have known what they were."

The colony is very young, just a layer thick, so it's recently formed. One thing that is puzzling scientists is why its chosen this spot.

"There is some unusual set of circumstances that occurs just here that doesn't occur even 10 metres away along the beach," said Professor Cooper.

"So whatever it is, it's very special to this particular time and space."

One clue could be the myriad of shells in the grass banks just about the tiny pool. Rain water is leaching through the ground and the shells, dissolving out calcium carbonate and carrying to the stromatolites.

Image caption Stromatolites' appearance on this planet is seen as a turning point in the earth's evolution

The blue-green algae that form the stromatolites helped create our present atmosphere by breaking down carbon dioxide and excreting oxygen. Their appearance on this planet is seen as a turning point in the earth's evolution.

While living examples are thought to be rare, it could be that we haven't found them because we aren't looking for them.

"The chances are that they may be more widespread than we actually know", explained Professor Cooper.

"Geologists have spent a lot more time studying the ancient stromatolites that are two billion years old than we have spent on living stromatolites.

"So this is an important site where we can look at the circumstances in which stromatolites actually occur."

News of the find is only starting to leak out but its expected to start a frenzied search around the coast of Ireland to see if there is more of this primitive organism to be discovered.