Wild West Yorkshire, Friday 19 November 2010

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Streaks of blue-green algae on the cooling towers of Ferrybridge

stromatolitesMalham CoveTHESE TINY stromatolites (left) in a fossil from Canada, each about one inch across, were built up layer by layer on the seabed from calcium carbonate secreted by cyanobacteria, also known as blue-green algae. Once thought to be algae, they're now grouped with the bacteria and, along with archaea, classified as prokaryotes.

Prokaryote cells have DNA but unlike eukaryotes the cells have no membrane-bound nucleus. We're made up of eukaryote cells but our health depends on a variety of prokaryote cells - the 'friendly bacteria' in advertisements for Yakult fermented milk drink - that are active in our digestive systems.

Stromatolites appear right at the start of the fossil record 3,800 million years ago and they're still with us today, in places like Shark Bay, Australia, where extreme conditions limits competition from other life forms. Stromatolites are often much larger than my pocket-sized examples - the size of a family car, for example. Blue-green algae can be seen close to home as streaks on the cooling towers of power stations, such as Ferrybridge (above). The blackish streaks of blue-green algae at Malham Cove (right) gave Charles Kingsley the idea that they might have been made by a chimney sweep's boy sliding down the face of the cliff, inspiring his story The Water Babies.

Microscopic as they are, the cyanobacteria were crucial in the story of life as they were the first organisms to use photosynthesis, releasing oxygen into the atmosphere. Cyanobacteria contain not only chlorophyll a, a green pigment, but also blue phycobilin, which combine to give the blue-green, almost blackish colour.

My thanks to my namesake, Canadian geologist Richard T Bell, for this fossil. He found a bed containing these tiny stromatolites while surveying an area of the Rocky Mountains.

Richard Bell, illustrator

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