The day life ends on Earth

By Pierre Barthélémy

Posted on April 12, 2021 at 6:30 p.m. – Updated on April 13, 2021 at 6:20 a.m.

Let’s face it, the news from planet Earth is hardly encouraging: a pandemic still not under control that will kill millions of people, a global warming that we are slow to fight while it turns ecosystems upside down and weakens entire populations, an accelerated erosion of biodiversity… Yet, with hindsight, it can be said without cynicism that, despite all this, life will continue, even if we eradicate ourselves in a thermonuclear Armageddon.

Life will continue as it did after each of the five great extinctions that have punctuated the last 500 million years and each time wiped out more than three quarters of species. Yes, life, stubborn, ingenious, resilient, will continue … Until the day when the physico-chemical conditions on the surface of our globe will force it to surrender.

An eschatological story, the description of the long journey towards this day of hell or nothingness, is what contains an article published in early March in Nature Geoscience and signed by the Japanese Kazumi Ozaki (Toho University, Funabashi) and the American Christopher Reinhard (Georgia Institute of Technology).

It examines the evolution of the presence of oxygen in the atmosphere. This molecule has not always been present on Earth: “At the beginning of our planet’s history, the atmosphere was very rich in CO2, recalls Benjamin Charnay, researcher at the CNRS, specialist in the atmosphere of the primitive Earth and that of exoplanets. It’s in this oxygen-free environment that life originated just over 3.8 billion years ago as single-celled organisms, some of which were expected to produce methane. “

The “snowball” effect of oxygen

“Oxygenic photosynthesis appeared between 3 billion and 2.7 billion years, continues Benjamin Charnay. It uses light to form biomass from carbon dioxide and it is a much more efficient mechanism for this than that of methanogenic organisms. ” As we learn in college, photosynthesis allows the beings who use it to capture the carbon atom of CO2 and release the oxygen we breathe.

“Atmospheric oxygen is a product of biology, underlines Purificacion Lopez-Garcia, research director at CNRS and specialist in microbial evolution. It was first produced by cyanobacteria and all current oxygenic photosynthesis derives from them. Chloroplasts, organelles responsible for photosynthesis in plants, are the derivatives of these ancient bacteria. ” During a process called endosymbiosis, algae and plants have somehow ingested and integrated cyanobacteria to join their services.

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The day life ends on Earth

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