A GENE study that pieced together the family tree of an ancient organism has overturned a long-standing belief about the creature鈥檚 role as life on Earth emerged.
Till now, cyanobacteria were believed to be among the first life forms on Earth. Because they produce oxygen as a by-product of photosynthesis, they have been credited with making the gas abundant in an atmosphere previously consisting mainly of nitrogen and carbon dioxide. This oxygen is believed to have reacted with iron dissolved in the oceans to produce the vast bands of iron oxides found in sedimentary rocks.
But Carrine Blank, a geobiologist at Washington University in St Louis, Missouri, says scientists need to rethink the role of cyanobacteria. She compared 38 genes belonging to 53 different species of living bacteria, including cyanobacteria, and used the data to construct a family tree in which species with the most similar genes were descended from a common ancestor.
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She concluded that rather than being one of the first bacteria to evolve, cyanobacteria must have been one of the last, emerging about 2.4 billion years ago. While this date coincides with the sudden rise in oxygen in the atmosphere around 2.3 billion years ago, it is around a billion years later than the time when banded iron structures are known to have formed. If she is right about cyanobacteria, they can鈥檛 have been responsible for producing the bands of iron oxide.
Blank鈥檚 revised history of cyanobacteria helps explain why there is no evidence of these organisms during the early deposition of the iron oxide bands and why oxygen didn鈥檛 become abundant until more recently in the Earth鈥檚 history. 杏吧原创s, meanwhile, must now rethink what produced the bands of iron oxide.
