3.6 billion years ago our planet already had a source of oxygen that could have been used by the first organisms that populated it. Those responsible would have been primitive microbes capable of photosynthesis, a process in which solar energy is transformed into chemical energy and that gas is released. Tanai Cardona, a biochemist in the Department of Life Sciences at Imperial College London, assures that this phenomenon already took place some one billion years earlier than has been believed, that is, shortly after – at least if we have in account of the geologic time scale – of life arising on Earth.
In a study published in the journal Heliyon , Cardona highlights that this finding will shed some light on the origin of biogenic oxygen, a fundamental aspect to understand the evolution of life in our world. Thus, it suggests that the first microorganisms that produced it were not cyanobacteria – one of the most widespread hypotheses today – but that they appeared later, and that even simpler bacteria made it before them. “The processes that sustain most of life on Earth could have been going on long before we suspect. The availability of oxygen at such an early time allowed microbes to diversify and dominate the planet for millions and millions of years ; it is, in essence, what made it easier for them to leave the cradle in which life originated and to spread to all corners of the globe ”, Cardona explains in a statement.
Life, much older
There are two varieties of photosynthesis: oxygenic, in which solar energy is used to break water molecules, which releases electrons, protons and oxygen; and anoxygenic, where this is not produced and in which other compounds and minerals are used, such as hydrogen sulfide, iron or arsenic. In general, the most widespread position is that this second type of photosynthesis appeared much earlier than the first and that, in fact, the Earth’s atmosphere did not contain oxygen until between 2.4 and 3.000 million years ago. However, Cardona points out that oxygenic photosynthesis would have existed much earlier, which means that complex life forms could have evolved earlier as well.
To determine this, he has studied in detail the photosystems, protein complexes where the photosynthetic pigments that are involved in the transformation of light energy are found. Although the mentioned oxygenic and anoxygenic photosynthesis use an enzyme called photosystem 1, it presents certain variations in one and the other. If it were possible to find out when the genetic differentiation that made this possible occurred, it would be possible to know when oxidative photosynthesis first took place. Well, Cardona discovered that these changes occurred around 3.6 billion years ago and that photosystems evolved much faster at first. Now, he hopes his findings will help astrobiologists looking for signs of life on other planets.
Image: Cyanobacteria. Josef Reischig / CSC via Wikimedia – CC
Referencia: Early Archean origin of heterodimeric Photosystem I.Tanai Cardona.Helyon (2018). DOI: 10.1016/j.heliyon.2018.e00548
