The scientific community accepts dating back to 2.7 billion years the first uncontested proofs of life on Earth. Beyond that, it’s a real free for all. But the ULg biologist and geologist Emmanuelle Javaux and two of her American and Canadian colleagues have succeeded in pushing back this time. Their discovery: microorganisms – thus proofs of life on earth – which they have dated, with supporting evidence, to 3.2 billion years ago. A world first, well worth a publication in the journal, Nature.

It is known that life appeared on Earth very early, but scientists don’t agree on the exact date. It is nonetheless there is general acceptance with dating it to the end of the Achaean (the mid Pre-Cambrian period), around 2.7 billion years ago, after an intense period of bombardment by meteorites. Beyond that, controversy blazes furiously. But, for the first time, a team made up of the spectroscopist Craig P. Marshall, from the University of Kansas, Andrey Bekker, a geologist and geochemist from the University of Manitoba, who specializes in carbon isotopes, and the biologist and geologist Emmanuelle Javaux from the University of Liège, a specialist in micro-palaeontology, have discovered microorganisms, of a relatively large size, cohabiting with the microbial mat in the photic zone (still accessible to the Sun’s rays) in coastal sea areas dating back to…3.2 billion years ago! In plain language: incontestable proofs of life going back to this period.

A few reference points. Around 4.56 billion years ago, the first telluric planets, including the Earth, Mercury, Venus and Mars, appeared in the solar system. Oxygen, for its part, appeared on Earth around 2.3 billion years ago with the appearance of the cyanobacteria, which produce photosynthesis and cast out oxygen. Through their metabolism they would profoundly change the planet and encourage the development of more complex living organisms (eukaryotes). The first signs of terrestrial life, which are not subject to controversy, date back to 2.7 billion years. The first of the Earth’s colonizers were the bacteria and the archaea, which are called prokaryotes because they have no nucleus. The eukaryotes, these single or multi cellular organisms which have for their part a nucleus, a cytoskeleton and organelles, appeared around 1.9 billion years ago, or, and this is more controversial, 2.7 billion years ago. It is precisely these tiny organisms that Emmanuelle Javaux takes an interest in through her research, in working, more precisely, to know and understand when and how these three groups appeared and evolved on Earth. The period of her research is the pre-Cambrian, which itself consists of three distinct periods: the Hadean (4.56 to 4 billion years), the Achaean, over the course of which life appeared (from 4 to 2.5 billion years), and finally the Proterozoic (from 2.5 to 544 million years), itself subdivided into the Paleo-, Meso-, and Neo- Proterozoic.