2023-07-19 17:54:00
We often forget it, but science is not set in stone. According to the Austrian philosopher Karl Popper, a theory is “scientific” only if the principles that constitute it lead to at least one prediction that is sufficiently precise to be tested by an experiment (or a measurement) likely to refute it. [La Logique de la découverte scientifique, 1934].
For 70 years, one theory has prevailed regarding the emergence of complex life: the “control by oxygen” hypothesis. According to this, the increase in oxygen concentrations would have favored the rise of multicellular beings in the oceans 575 million years ago.
Qualified “Avalon Blast”this episode saw the birth of the “Ediacaran wildlife” – named following the hills in Australia where the fossils of these organisms were discovered.
However, researchers from the University of Copenhagen (Denmark), together with colleagues from the Woods Hole Institute of Oceanography (USA), the University of Southern Denmark and Lund University (Sweden) , among others, have revealed clues that tend to contradict this theory. They presented their findings in the journal Geobiology (May 8, 2023).
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Oxygen concentrations that have increased little
By studying the chemical composition of ancient rock samples from a mountain range in Oman – which was, at the time of the Avalon explosion, at the bottom of the ocean – the researchers were able to measure the isotope concentrations of two chemical elements (thallium and uranium) and deduce the oxygen concentrations at this period.
Their results suggest that oxygen concentrations on Earth did not increase at that time. Levels remained five to ten times lower than today, which is roughly the amount of oxygen found at twice the height of Mount Everest.
“Our measurements give a good idea of the average oxygen concentrations in the world’s oceans at the time. It seems obvious to us that there was no major increase in the amount of oxygen when the fauna more advanced began to evolve and dominate the Earth. In fact, there was a slight decrease”explains Christian J. Bjerrum, professor at the University of Copenhagen, co-author of the study, in a communiqué.
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Analogy with stem cells
He advances, without however being able to prove it, the opposite theory: complex life would have emerged thanks to a concentration of oxygen not high… but low! “Interestingly, the rise of multicellular organisms occurred at a time when atmospheric and oceanic oxygen concentrations were low. This indicates that organisms [en] have benefited […] and were able to grow in peace, with the water chemistry protecting their stem cells.”
The scientist refers to cancer research. His colleagues at Lund University observed that low oxygen levels were essential to keep stem cells under control until they differentiated into a specific type of cell, such as a muscle cell for example. .
“With too much oxygen, cells grow and, in the worst case, mutate wildly and die. It is far from inconceivable that this mechanism was applied at the time”concludes Professor Bjerrum.
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Rewrite textbooks? Not so sure
“The fact that we now know, with a high degree of certainty, that oxygen did not control the development of life on Earth provides us with an entirely new story of how life arose and the factors that have controlled this success”, estimates Professor Bjerrum in the press release. Before adding:
“That means we have to rethink a lot of things that we’ve believed to be true since childhood. And school textbooks have to be revised and rewritten.”
However, the debate is far from over. A research paper alone cannot resolve a decades-long controversy.
It should also be remembered that well before the Ediacaran, multicellular life emerged for the first time 2.1 billion years ago, according to the work of Pr El Albani of the University of Poitiers and his colleagues (CNRS2014). “The emergence of this biodiversity follows the first increase in oxygen in the Earth’s atmosphere, regarding 2.3 billion years ago”explained the researcher.
On the same topic :
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⋙ “Ctenophore”: this strange form of life is the first animal to have lived on Earth
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