Prior to oxygen photosynthesis, the Earth, about 2.5 billion years ago, was dominated by anaerobic life forms in an oxygen-poor environment. The oceans contained mainly bacteria using chemical processes without oxygen release, while the Earth's atmosphere consisted mainly of carbon dioxide, nitrogen and methane. This precambrian period prepares the ground for a major biological and geochemical transformation.
Geological and biological background before oxygenated photosynthesis
The primitive Earth was characterized by a dense sky and a reductive atmosphere, without free oxygen. Unicellular organisms, mainly archaeus and bacteria, flourished in anaerobic environments. Geological conditions favoured the formation of sedimentary rocks rich in non-oxidized iron, indicating the absence of significant atmospheric oxygen. Biologically, cyanobacteria emerged as the first cells capable of oxygen photosynthesis, using water as an electron donor and releasing oxygen.
Impact of oxygenated photosynthesis on the atmosphere and life
The appearance of oxygenated photosynthesis caused a progressive accumulation of oxygen in the atmosphere, profoundly altering terrestrial chemistry. This phenomenon, known as Great Oxidation, led to the oxidation of oceanic ferrous masses and the formation of iron deposits. Oxygen became a powerful breeding agent, causing the extinction of sensitive anaerobic organisms while promoting the emergence of more complex aerobic organisms. This transformation opened the way to biological diversification and the formation of a protective atmosphere against UV radiation.
Historical links
Oxygen photosynthesis precedes the formation of the first forms of multicellular life around -600 million years, conditioned by an oxygen-rich environment. It is directly related to the Great Oxidation (-2,4 billion years), which marks a planetary upheaval. Finally, it anticipates the Cambrian explosion (-541 million years), a period of rapid diversification of multicellular organisms, made possible by the environmental changes initiated by this photosynthesis.
