Chapter Sixteen

Cyanobacteria

16.1   And so we pause for a moment in our sprint through the history of the evolution of life on earth, still hundreds of millions of years ago, and well before most animals and plants that we are familiar with today had evolved, because we have already arrived at the main elements of the microbiological community we call Lake Annecy, with its four main players, Cyanobacteria, Algae, Rotifers and Crustacea (Daphnia, Copepods) which between them account for 95% of the biomass in the Lake, as compared with all the fish who account for just 1 %.   Lake Annecy really does tell a story of ancient life on this planet, evolved well before all the plants, animals and birds we now see above the water’s surface.

16.2   Cyanobacteria and the evolution of photosynthesis

16.3   The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geological record indicates that this transforming event took place early in Earth's history, at least 2450–2320 million years ago, and, perhaps, much earlier. Because the Earth's atmosphere contained almost no oxygen during the estimated development of photosynthesis, it is believed that the first photosynthetic cyanobacteria did not generate oxygen. However, by about 2000 million years ago there was already a diverse biota of blue-green algae. Cyanobacteria remained the principal primary producers of oxygen throughout the 2 billion years of the Proterozoic Eon. Green algae joined cyanobacteria as the major primary producers of oxygen only near the end of the Proterozoic, and it was only with the Mesozoic (251–65 Ma) that radiations of dinoflagellates, coccolithophorids, and diatoms contributed the primary production of oxygen in marine shelf waters. Cyanobacteria remain to this day critical to marine ecosystems as primary producers of oxygen in oceans as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae.

Continue Reading   Chapter Seventeen