A new study based on the analysis of the genomes of current microbes has made it possible to determine the date of their oldest common ancestor, which is also certainly our ancestor: it would be 4.2 billion years old! A result that supports the idea that life appeared very early in Earth's history.
When did life appear on Earth? This question has long been debated, due to the lack of fossil evidence. In 2022, traces of microbial activity revealed that colonies of bacteria called stromatolites were already present 3.48 billion years ago, reinforcing the idea that life could have appeared much earlier in Earth’s history, around 3.8 or even 4 billion years ago.
Molecular clock enables date of oldest common ancestor
A new study suggests that the first bacteriabacteria It is possible that they appeared much earlier, 4.2 billion years ago. This conclusion is based on the analysis of the genomes of 700 species of modern microbes. The aim was to reconstruct their evolutionary history, or even to go back to the oldest common ancestor. In 2016, a study based on the same principle made it possible to say that these primitive bacteria were anaerobic, that is, they lived in an environment completely devoid of oxygen, and that they were certainly also thermophilic. Characteristics that then strengthened the idea that life appeared at hydrothermal sources located at the bottom of the oceans.
Since then it has evolved. SequenceSequence The new microbes have made it possible to improve this hypothesis, by significantly delaying the age of the appearance of this first common ancestor. By monitoring the evolution of mutations GeneticsGenetics Among different microbial species, researchers from the University of Bristol have managed to create a type ofmolecular clockmolecular clock Allowing them to reconstruct the evolutionary tree of these MicroorganismsMicroorganisms.
bacteria that would have lived on the surface
Published In the magazine Nature and Evolution EnvironmentThe results therefore indicate an age of 4.2 billion years for the oldest common ancestor. Thus, life could have appeared only 340 million years after the formation of the Earth! The study also allows us to draw a picture of these first bacteria: they were certainly anaerobic, and they were found to be anaerobic. energyenergy In CO composition2 And h2But the findings go further than that. In fact, it appears that these bacteria possess embarrassedembarrassed allowing them to protect themselves from radiation ultravioletultravioletWhich suggests that they lived in the surface waters and not in the depths! They would then have captured carbon dioxide.2 And h2 from'AtmosphereAtmosphere.
This result does not necessarily conflict with the hypothesis of origin at the level of Hydrothermal resourcesHydrothermal resourcesThe researchers also noted the presence ofEnzymesEnzymes Typical of heat lovers. It is therefore possible that the first bacteria diversified very quickly in order to colonize different environments.
primitive immune system
Surprisingly, the researchers also discovered the presence of CRISPR-Cas9 genes, which are currently known to be used to repair genetic materialgenetic material It is degraded by viral invasions. This is a particularly striking result, because it suggests that the first bacteria already had some kind of immune systemimmune systemWithin a few million years, life will have taken major steps that will allow living organisms to emerge.Appearance ofAppearance of Complex bacteria and buildingBuilding from U.S environmental systemenvironmental system basic.
