Saturday, 15 October 2011

A New Living Fossil - The Life Of Stromatolites

Pools of water at the Giant's Causeway, Ireland
Stromatolites are some of the oldest known macroscopic fossils on Earth. Some are over 3.5 billion years old, very close to the emergence of life itself and are invaluable to scientists. Apart from adding to the fossil records of the precambrian, the stromatolites preserve the conditions of the water and the atmosphere in which they form, and allow us to build up a greater picture of the young Earth and how it evolved as a planet. We see them in all parts of the fossil record and they can be found worldwide.

Stromatolites are colonies of photosynthetic cyanobacteria (more commonly known as blue green algae).   They form only when bacteria divide and grow and excrete carbonates which form a solid dome over the top of the colony. These grow over thousands of year to heights that can reach a metre. While most stromatolites colonies are fossils, some parts of the world still harbour these incredible conglomerations. These are generally inhospitable to all other lifeforms as stromatolites require very exact conditions in which to evolve.

Famous examples are those found in the hyper-saline stretch of water at Shark Bay, Australia, or a recent discovery of metre tall formations in the freezing cold, and the almost pitch black environment, of some sub-glacial, Antarctic lakes. These locations are very remote and can support very few lifeforms. On the other hand they have remained undisturbed for millions of years. Yet you would not expect to find these marvels of nature in a little grey pool of cold, brackish water on the Giant's Causeway, Ireland.
Each bulge represents a stromatolite formation.
However they are all restricted to this one pool

Against all the odds, they were found in this unlikely location by Professor Andrew Cooper from the School of Environmental Sciences whilst looking for very different, geological formations. '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."

Whist it is very young, just a layer thick, the discovery is definitely a stromatolite. It is surprising in two ways. The first is that the Giant's Causeway is regularly bombarded by violent storms and supports a myriad of different organisms which could easily damage or even eat such a fragile structure. The second interesting point is that Cooper and a team of scientists found no other stromatolites in the area. So there must have been a set of conditions which made this pool unique and stromatolite friendly.

As news of the discovery spreads, it is likely that a frenzied search will begin along the coast of Ireland to find more of these colonies. The unique conditions within the pool will be a great asset as they will help scientists understand when and where stromatolites may have formed, are forming, or indeed will form. One possible hypothesis for the pool's unique nature is that rain water and storms cause the shells of molluscs, such as limpets, living around the pool to be eroded, supplying the stromatolite directly with the carbonates needed for its formation. While this condition is fairly specific, the placement of the pool shows that stromatolites are more hardy than originally thought. This new knowledge gives us a greater understanding as to how these miracles first evolved and how life was a global phenomenon at a very early stage.