New research challenges the long-standing belief that increased oxygen levels triggered the emergence of complex multicellular organisms during the Avalon explosion, a precursor to the renowned Cambrian explosion that occurred between 685 and 800 million years ago.
Previously, it was thought that higher oxygen concentrations facilitated the evolutionary development of advanced marine organisms. However, a study conducted by researchers from the University of Copenhagen, in collaboration with Woods Hole Oceanographic Institute, the University of Southern Denmark, and Lund University, among others, suggests otherwise.
The team analyzed the chemical composition of ancient rock samples from the Oman Mountains to determine oxygen concentrations in Earth’s oceans during the appearance of multicellular organisms. Surprisingly, the results showed that oxygen levels had not significantly increased during that period. In fact, they remained 5-10 times lower than present-day levels, comparable to the oxygen found at twice the height of Mount Everest.
Associate Professor Christian J. Bjerrum, who has extensively studied the origin of life, explains, “Our measurements provide a good picture of what average oxygen concentrations were in the world’s oceans at the time. And it’s apparent to us that there was no major increase in the amount of oxygen when more advanced fauna began to evolve and dominate Earth. In fact, there was somewhat of a slight decrease.”
This finding challenges the established understanding of the role of oxygen in the development of advanced life forms on Earth. It necessitates a reevaluation of existing knowledge and calls for revisions to textbooks.
While the researchers acknowledge the many unknowns and controversies surrounding this topic, Bjerrum hopes that their findings will encourage scientists worldwide to reinterpret their previous research and data in light of the notion that oxygen was not the driving force behind the development of life.
The study’s results raise the question of what triggered the explosion of life during that era if not oxygen. Bjerrum suggests that low oxygen levels might have played a role, offering protection to organisms’ stem cells and allowing them to develop peacefully. This phenomenon has been observed in cancer research, where low oxygen levels help regulate stem cells until an organism determines their specific type of cell development.
The research team analyzed rock samples from various locations, including the Oman Mountains, which were submerged during the Avalon explosion. Fossils from three different mountain ranges worldwide—Oman Mountains (Oman), Mackenzie Mountains (NW Canada), and the Yangtze Gorges area of South China—confirmed the findings. By examining the chemical composition of layers in the seabed formed by the deposition of clay and sand, the researchers gained insights into ocean chemistry from hundreds of millions of years ago.
The study employed Thallium and Uranium isotopes found in the mountains to estimate oxygen levels during the relevant period. The findings challenge the long-held belief that oxygen was the primary driver of the development of complex life forms, shedding new light on the conditions and factors that contributed to the success of life’s emergence on Earth.
