No, oxygen didn’t catalyze the swift blossoming of Earth’s first multicellular organisms

Life on Earth didn’t arise as described in textbooks.


It has proven challenging to reconstruct the ocean’s oxygenation history throughout the Ediacaran period (635 to 539 million years ago), which has sparked a divisive dispute concerning the ecosystems that supported the emergence of life. The Shuram excursion, the greatest negative inorganic C-isotope excursion known in the geologic record, and whether this artifact reflects the global-scale oxygenation of Earth’s deep seas are central to this argument.

To help resolve this debate, scientists- from the University of Copenhagen researchers working together with colleagues from Woods Hole Oceanographic Institute, the University of Southern Denmark, and Lund University, among others- conducted a detailed geochemical investigation of two siliciclastic-dominated successions from Oman deposited through the Shuram Formation.

Scientists were able to “measure” the oxygen levels in the world’s oceans when these multicellular animals first emerged by analyzing the chemical composition of ancient rock samples from an Omani mountain range. Contrary to expectations, the outcome demonstrates that oxygen levels on Earth did not rise. Levels remained 5 to 10 times lower than they are now, or about the same amount of oxygen at a height twice that of Mount Everest.

The measurements offer a good picture of what average oxygen concentrations were in the world’s oceans. And it is clear to us that the amount of oxygen did not significantly rise as more sophisticated animals started to emerge and take over the planet. In reality, there was a slight decrease.

The latest finding ends a 70-year study saga emphasizing the importance of higher oxygen concentrations in our planet’s evolution of complex life. Now, it’s certain that oxygen didn’t control the development of life on Earth. The study tells a new story about how life arose and what factors controlled this success.

Associate Professor Christian J. Bjerrum, who has been quantifying the conditions surrounding the origin of life for the past 20 years, said, “Specifically, it means that we need to rethink many of the things that we believed to be true from our childhood learning. And textbooks need to be revised and rewritten.”

The latest finding ends a 70-year study saga that emphasizes the importance of increasing oxygen concentrations in our planet’s evolution of complex life.

Scientists noted, “There are many research sections around the world, including in the United States and China, that have done lots of research on this topic, whose earlier results may shed important new details if interpreted on the basis that oxygen didn’t drive the development of life.”

The same effect, the scientist claims, has been investigated in both human and animal stem cells used in cancer research. Here, scientists from Lund University found that low oxygen levels are essential for controlling stem cells until an organism determines that the cell should develop into a particular type of cell, such as a muscle cell.

Christian J. Bjerrum said“We know that animals and humans must be able to maintain low concentrations of oxygen to control their stem cells and, in so doing, develop slowly and sustainably. With too much oxygen, the cells will develop and, in the worst case, mutate wildly and perish. It is far from inconceivable that this mechanism applied back then.”

Scientists performed the analyses using Thallium and Uranium isotopes found in the mountains. Scientists extracted data from these isotopes, and while doing so, they calculated oxygen levels from hundreds of millions of years ago.

Journal Reference:

  1. Chadlin M. Ostrander, Christian J. Bjerrum, Anne‐Sofie C. Ahm, Simon R. Stenger, Kristin D. Bergmann, Mohamed A. K. El‐Ghali, Abdul R. Harthi, Zayana Aisri, Sune G. Nielsen. Widespread seafloor anoxia during generation of the Ediacaran Shuram carbon isotope excursion. Geobiology, 2023; DOI: 10.1111/gbi.12557