Newswise — Contrary to a 70-year-old assumption, the rapid emergence of Earth's first multicellular organisms during the Avalon explosion, which occurred approximately 685 to 800 million years ago, was not catalyzed by oxygen. This event preceded the well-known Cambrian explosion and marked a significant shift in the Earth's oceans. The prevailing life forms at that time, such as small single-celled amoebas, algae, and bacteria, which had dominated the planet for over 2 billion years, were replaced by enigmatic multicellular organisms like sea sponges.
Until now, the prevailing belief was that the evolutionary emergence of more advanced marine organisms was triggered by an increase in oxygen levels. However, a collaborative effort between researchers from the University of Copenhagen, Woods Hole Oceanographic Institute, the University of Southern Denmark, Lund University, and others is challenging this notion.
By analyzing the chemical composition of ancient rock samples obtained from a mountain range in Oman, the researchers have been able to estimate the oxygen concentrations in the Earth's oceans during the period when these multicellular organisms first appeared. Surprisingly, their findings contradict expectations, as they reveal that Earth's oxygen concentrations had not actually risen. Instead, the oxygen levels remained 5-10 times lower than what they are today, roughly equivalent to the amount of oxygen found at twice the height of Mount Everest.
Associate Professor Christian J. Bjerrum, who has dedicated the last two decades to studying the conditions surrounding the origin of life, explains the significance of their measurements. The research has provided a clear picture of the average oxygen concentrations in the Earth's oceans during that period. Surprisingly, the data indicates that there was no significant increase in oxygen when more advanced marine life began to evolve and dominate the planet. In fact, there seems to have been a slight decrease in oxygen levels during that time.
Revises our understanding of life’s origins
The recent findings conclusively refute a 70-year-old research narrative that emphasized the crucial role of higher oxygen concentrations in the evolution of advanced life forms on Earth.
According to the researcher, the newfound certainty that oxygen did not play a controlling role in the development of life on our planet opens up an entirely fresh perspective on how life originated and what factors truly influenced its success. This realization prompts a need to reevaluate many long-held beliefs acquired since childhood learning. It also calls for a revision and rewriting of textbooks to reflect this groundbreaking discovery.
Despite the progress made, there are still many unknowns and controversies in this field of research. Associate Professor Bjerrum expresses the hope that their latest findings will inspire researchers globally to reassess their previous results and data from a fresh perspective.
He emphasizes that numerous research groups worldwide, including those in the United States and China, have conducted extensive studies on this subject. These earlier results could potentially offer valuable new insights when reinterpreted under the premise that oxygen did not play a primary role in driving the evolution of life on Earth.
Absence of oxygen may have aided development
If not increased oxygen, then what could have caused the remarkable explosion of life during that era? The researcher offers a contrasting perspective:
"It's intriguing that the proliferation of multicellular organisms coincided with a period of low atmospheric and oceanic oxygen levels. This suggests that these organisms thrived in an environment with reduced oxygen and were able to develop undisturbed, as the water chemistry naturally protected their stem cells," explains Christian J. Bjerrum.
The researcher draws parallels to cancer research, where similar phenomena have been explored in the stem cells of humans and other animals. At Lund University, colleagues observed that maintaining low oxygen levels is vital for regulating stem cells until an organism signals the need for these cells to develop into specific cell types, such as muscle cells.
"We understand that animals and humans must carefully control oxygen concentrations to manage their stem cells, allowing for slow and sustainable development. Excessive oxygen could lead to uncontrolled cell growth and, in the worst-case scenario, erratic mutations and cell death. It is entirely plausible that a similar mechanism played a role in the past," concludes Christian J. Bjerrum.
Box 2: Fossils from Oman
In their recent study, the researchers conducted an analysis of rock samples collected from various locations, including the Oman Mountains in northern Oman. These mountains, despite being elevated and arid in the present day, were once situated on the seabed during the rapid proliferation of diverse organisms known as the Avalon explosion.
The team's findings were further corroborated by examining fossils from three distinct mountain ranges across the globe: the Oman Mountains (Oman), Mackenzie Mountains (NW Canada), and the Yangtze Gorges area of South China.
Over time, sediments such as clay and sand from the land find their way into the sea, eventually settling in layers on the seabed. By carefully examining the chemical composition of these layers and delving deep into them, researchers can gain insights into the ocean's chemistry during specific geologic periods.
To determine the oxygen levels from hundreds of millions of years ago, the researchers utilized Thallium and Uranium isotopes found in the mountains. Extracting data from these isotopes allowed them to calculate the oxygen levels prevalent during that ancient era.
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