The emergence of complex life on Earth: scientists contradict the theory of “oxygen control”

We often forget this, but the science is not set in stone. According to the Austrian philosopher Karl Popper, a theory is “scientific” only if the principles that make it up lead to at least one prediction that is accurate enough to be tested by an experiment (or measurement) that is likely to disprove it. [La Logique de la découverte scientifique, 1934].

For 70 years, one theory about the emergence of complex life has prevailed: the “oxygen control” hypothesis. According to this, an increase in oxygen concentrations would have given rise to multicellular organisms in the oceans 575 million years ago.

Eligible “Avalon Blast”and this episode witnessed the birth of “Wildlife in Ediacaran” – Named after the hills in Australia where fossils of these organisms were discovered.

However, researchers from the University of Copenhagen (Denmark), together with colleagues from the Woods Hole Oceanographic Institution (USA), University of Southern Denmark and Lund University (Sweden), among others, have uncovered evidence that tends to contradict this theory. They presented their findings in the journal biology (May 8, 2023).

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Oxygen concentrations that increased slightly

By studying the chemical composition of ancient rock samples from a mountain range in Oman — which, at the time of the Avalon eruption, was on the ocean floor — the researchers were able to measure isotopic concentrations of two chemical elements (thallium and uranium) and infer oxygen concentrations for the period.

Their results indicate that oxygen concentrations on Earth did not increase in that time. Levels remained five to ten times lower than they are 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 that time. It seems clear to us that there was no significant increase in the amount of oxygen when the most advanced animals began to evolve and dominate the land. In fact, there was a slight decrease.”Explains Christian J. Byrom, a professor at the University of Copenhagen and co-author of the study, V.A communication.

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Similar to stem cells

He advances, without being able to prove it, the opposite theory: complex life would have arisen thanks to a not high … but low oxygen concentration! “Interestingly, the emergence of multicellular organisms occurred at a time when oxygen concentrations in the atmosphere and oceans were low. This indicates that living organisms [en] They took advantage […] And they were able to grow in peace, as the chemistry of the water protected their stem cells.”

Scientist refers to cancer research. His colleagues at Lund University noticed that lower oxygen levels were necessary to keep the stem cells in check so that they would differentiate into a specific type of cell, like a muscle cell for example.

“With so much oxygen, cells grow and, in the worst case, randomly develop and die. It is inconceivable that this mechanism was applied at that time.”Professor Jerome concludes.

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Rewrite textbooks? Not sure about that

“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 about how life originated and the factors that controlled this success.”Professor Bjerrum said in the press release. before adding:

“It means we have to rethink a lot of the things that we thought were right from childhood. Textbooks need to be revised and rewritten.”

However, the debate is not over yet. The paper alone cannot resolve the decades-old controversy.

It should also be remembered that before the Ediacaran period, multicellular life first appeared 2.1 billion years ago, according to the work of the Albanian professor from the University of Poitiers and his colleagues (CNRS2014). “The appearance of this Biodiversity Follows the first increase in oxygen in the Earth’s atmosphere, about 2.3 billion years ago.Researcher’s explanation.

On the same topic:

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⋙ “Ctenophore”: This strange life form is the first animal to live on Earth