Our planet became oxygenated thanks to cyanobacteria

2019/12/11 Agirre Ruiz de Arkaute, Aitziber - Elhuyar Zientzia Iturria: Elhuyar aldizkaria

• Eboluzioa
• Geologia

The oxygenation of the planet was key for the Earth to assume the life we know. It was essential for the creation of animals, for example. But it is not clear how the oxygenation process itself occurred. According to a mathematical model published by the journal Science, this complex process of oxygenation of the planet only needed simple photosynthetic cyanobacteria. No tectonic or biological revolution was necessary, as suggested so far.

The geological record shows that the process of oxygenation of the Earth, rather than being linear, took place in three major steps. In addition, they joined the development of more complex forms of life: in the first step, 2,4-2,2 billion years ago, the atmospheric oxygen level barely rose to 10-5 of the current O2. From that moment on, the atmospheric O2 followed a continuous progression and began to oxygenate the surface of the sea, although the deep waters continued in anoxia. In it emerged the first eukaryotes. In a second step, between 800 and 540 million years ago, the atmospheric oxygen level reached almost half of the current concentration and the oxygenation of the seabed occurred, although it was not yet stable in time or space. As a result, eukaryotes were diversified and the first animals appeared, becoming the main marine ecosystems. In a last step of oxygenation, already in the Paleozoic, atmospheric and oceanic oxygens reached current levels and stabilized 450-400 million years ago. From that moment on, the size and diversification of animals increased, with the specialization of predators and the evolution of terrestrial vascular plants.

The notoriety of these three oxygenation steps has led scientists to infer that developed life forms and Earth's tectonic evolution had a fundamental influence on the planet's oxygenation process. However, the new model of the English University of Leeds, taking into account the mere development of photosynthetic cyanobacteria, has succeeded in repeating the same three-step pattern seen in the geological register without the need for more surprises. Therefore, it has questioned the main hypotheses proposed so far.