Non, ce n'est pas l'oxygène. En fait, l'oxygène que nous respirons aujourd'hui a été produit par les plantes pendant des milliards d'années et était largement absent de l'atmosphère à l'origine.
La réponse est l'azote car cet élément est indispensable à la fabrication des gènes.
Mais voilà, cet élément n'est pas abondant dans les océans, là où la vie est d'abord apparue. Les premières formes de vie ont donc dû apprendre à utiliser l'azote qui est présent dans l'atmosphère terrestre et, selon cette récente étude, ils y sont arrivés beaucoup plus tôt que prévu:
Life can exist without oxygen, but without plentiful nitrogen to build genes – essential to viruses, bacteria and all other organisms – life on the early Earth would have been scarce.
The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago. Now research from the University of Washington looking at some of the planet’s oldest rocks finds evidence that 3.2 billion years ago, life was already pulling nitrogen out of the air and converting it into a form that could support larger communities.
“People always had the idea that the really ancient biosphere was just tenuously clinging on to this inhospitable planet, and it wasn’t until the emergence of nitrogen fixation that suddenly the biosphere become large and robust and diverse,” said co-author Roger Buick, a UW professor of Earth and space sciences. “Our work shows that there was no nitrogen crisis on the early Earth, and therefore it could have supported a fairly large and diverse biosphere.”