Oxygen levels didn’t cause the Cambrian explosion

New research has challenged a long-held assumption regarding the emergence of Earth’s first multicellular organisms. The Avalon explosion, which occurred between 685 and 800 million years ago, marked the appearance of complex multicellular life forms in the world’s oceans, replacing the dominance of single-celled amoebae, algae, and bacteria that had ruled the planet for over 2 billion years.

Traditionally, it was believed that this explosion of marine life was triggered by a significant increase in oxygen levels in the oceans. However, a groundbreaking study conducted by the University of Copenhagen in collaboration with researchers from the Woods Hole Oceanographic Institute, the University of Southern Denmark, and Lund University, among others, has shattered this notion.

Analyzing the chemical composition of ancient rock samples from an Omani mountain range, the scientists were able to gauge oxygen concentrations in the oceans during the time when these multicellular organisms emerged. Surprisingly, the findings revealed that Earth’s oxygen levels had not risen during that period. On the contrary, they remained 5-10 times lower than present-day levels, comparable to the amount of oxygen found at twice the height of Mount Everest.

Published in the journal Geobiology, the researchers’ paper provides a clear insight into the average oxygen concentrations in the ancient oceans. The results demonstrate that the rise of more advanced marine life forms did not coincide with a significant oxygen increase. In fact, there was even a slight decrease in oxygen levels during that time.

Associate Professor Christian J. Bjerrum, an expert in studying the conditions surrounding the origin of life, remarked on the significance of their measurements. The data convincingly indicates that the flourishing of advanced fauna in Earth’s oceans was not directly linked to a surge in oxygen but occurred despite lower oxygen concentrations.

This new understanding challenges the conventional belief and calls for a reevaluation of the factors that contributed to the emergence and domination of multicellular organisms during this transformative era.

Revising our understanding of life’s origins

The latest findings have definitively put an end to a 70-year-long research narrative that emphasized the crucial role of higher oxygen concentrations in the evolution of complex life forms on Earth.

“This discovery, which provides strong evidence that oxygen was not the controlling factor in the development of life on our planet, presents us with an entirely new perspective on the origins of life and the factors that influenced its success,” declares the researcher. They further emphasize the need to reevaluate and revise long-held beliefs that were ingrained in our early education. Textbooks, in particular, require updating to reflect this new understanding.

Despite the significant progress made, there are still numerous unknowns and controversies surrounding this subject. Consequently, the researcher hopes that these groundbreaking results will inspire scientists worldwide to reexamine their previous findings and data from a fresh perspective.

“There are various research groups across the globe, including in the United States and China, that have conducted extensive studies on this topic. Reinterpreting their earlier results in light of the fact that oxygen did not drive the development of life may reveal valuable new insights,” they state.

Absence of oxygen may have aided development

The era’s explosion of life might have been triggered by the opposite of what was previously believed, as suggested by Bjerrum’s research.

Surprisingly, the emergence of multicellular organisms coincided with a period of low atmospheric and oceanic oxygen levels. This implies that these organisms thrived in an environment with reduced oxygen and found it conducive to their development. Bjerrum speculates that the lower oxygen concentrations provided a protective environment for their stem cells, allowing them to evolve undisturbed.

Drawing parallels with cancer research and the behavior of stem cells in humans and animals, Bjerrum points out that low oxygen levels are essential for keeping stem cells in check until the organism decides on their differentiation into specific cell types, such as muscle cells.

It appears that maintaining low oxygen concentrations allowed for slow and sustainable development, preventing uncontrolled growth and mutations in the cells. In contrast, higher oxygen levels might have led to erratic and potentially fatal mutations. Therefore, it is plausible to consider that this mechanism played a crucial role during that ancient era.

Fossils from Oman

In this groundbreaking study, the researchers conducted an analysis of rock samples from various locations, including the Oman Mountains in northern Oman. Remarkably, despite their current elevation and arid conditions, these mountains were once part of the ocean floor during the rapid proliferation of diverse organisms known as the Avalon explosion.

To further validate their findings, the researchers also examined fossils from three different mountain ranges worldwide: the Oman Mountains in Oman, the Mackenzie Mountains in northwest Canada, and the Yangtze Gorges area in South China.

The process involved studying layers of clay and sand that originated from land and were subsequently washed into the sea, where they settled on the seabed over time. By examining the chemical composition of these sediment layers and descending through them, the scientists obtained valuable insights into the ocean’s ancient chemistry during the specific geological period under investigation.

The analysis focused on thallium and uranium isotopes found in the mountains. Extracting data from these isotopes allowed the researchers to calculate oxygen levels from an astounding span of hundreds of millions of years ago. This method provided a unique and accurate glimpse into the oxygen concentrations prevailing during the critical era when complex multicellular life forms first emerged and flourished.

The combination of data from diverse locations and precise isotopic analysis played a pivotal role in confirming the researchers’ groundbreaking conclusions about the relationship between oxygen levels and the explosion of life during the Avalon era.

Source: University of Copenhagen

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