Oxygen did not catalyze the rapid flowering of the first multicellular organisms on Earth. The results of a new study contradict a 70-year-old hypothesis about the cause of the explosion of ocean animals hundreds of millions of years ago.
Between 685 and 800 million years ago, multicellular organisms began to appear in all of Earth’s oceans during the so-called Avalon explosion, a precursor to the more famous Cambrian explosion. During this time, sea sponges and other unique multicellular organisms replaced the small single-celled amoebae, algae and bacteria, which until then, ran on the planet for more than 2 billion years.
Until recently, it was believed that the increase in oxygen levels caused the evolutionary arrival of more advanced marine organisms. This was confirmed by researchers at the University of Copenhagen working with colleagues from Woods Hole Oceanographic Institute, University of Southern Denmark and Lund University, among others.
By studying the chemical composition of ancient rock samples from the Omani mountains, researchers were able to “measure” the oxygen concentrations in the world’s oceans from when these multicellular organisms appeared. Contrary to expectations, the result showed that the oxygen concentrations on Earth did not increase. In fact, the levels remained 5-10 times lower than today, which is roughly how much oxygen there is twice the height of Mount Everest.
The paper was published in the journal Geobiology.
“Our measurements give a good picture of what the average concentration of oxygen in the world’s oceans was at the time. And it was obvious to us that there were no large increases in oxygen levels when the more advanced fauna began to -development and dominance on Earth. In fact, there has been a slight decline,” said Associate Professor Christian J. Bjerrum, who has been quantifying the conditions surrounding the origin of life for the past 20 years.
Changing our understanding of the beginning of life
The new result puts to rest a 70-year history of research that promotes the centrality of higher oxygen concentrations in the development of more advanced life on our planet.
“The fact that we now know with a high degree of certainty that oxygen did not control the development of life on Earth gives us a new story of how life arose and what factors that controls this success,” said the researcher, adding, “In particular, this means that we need to rethink many things that we believe to be true from our childhood learning. And books must be change and rewrite.”
There is still much that researchers do not know, as well as much controversy. Therefore, Bjerrum hopes that the new result will encourage other researchers around the world to reconsider their previous results and data in a new light.
“There are many research sections around the world, including in the United States and China, that have done a lot of research on this topic, whose preliminary results may provide important new details when interpreted on the basis of oxygen does not drive the development of. life,” he said.
The lack of oxygen may have helped the development
So, if not an excess of oxygen, what caused the explosion of life in the period? Perhaps the exact opposite, Bjerrum explained.
“It is interesting that the explosion of multicellular organisms occurs at a time with a low concentration of atmospheric and oceanic oxygen. That shows that the organisms benefited from the low level of oxygen and were able to develop peace, because the water chemistry protects their stem cells naturally,” he said.
According to the researcher, the same phenomenon was studied in cancer research, in stem cells of humans and other animals. Here, colleagues at Lund University observed that low oxygen levels are important for inhibiting stem cells until an organism decides that the cell needs to become a specific type of cell, such as a in muscle.
“We know that animals and humans must be able to maintain a low concentration of oxygen in order to control their stem cells, and in doing so, develop slowly and sustainably. mutate wildly and die. This is far from it is inconceivable that this mechanism was used before,” Bjerrum concluded.
Fossils from Oman
In the new study, researchers analyzed rock samples from—among other places—the Oman Mountains in northern Oman. While relatively high and very dry today, the mountains were at the bottom of the ocean during the Avalon eruption rapidly blooming the diversity of organisms.
The researchers confirmed their findings with fossils from three different mountains around the world: the Oman Mountains (Oman), Mackenzie Mountains (northwest Canada) and the Yangtze Gorges area of South China.
Over time, clay and sand from the land are washed into the sea, where they settle in the layers of the sea floor. By going through these layers and examining their chemical composition, researchers can get a picture of the chemistry of the ocean at a particular geologic time.
The analyzes were carried out using thallium and uranium isotopes found in the mountains, where the researchers were able to obtain data, and to do so, calculate the level of oxygen from hundreds of millions of years ago.
Chadlin M. Ostrander et al, Widespread seafloor anoxia during the generation of the Ediacaran Shuram carbon isotope excursion, Geobiology (2023). DOI: 10.1111/gbi.12557
Provided by the University of Copenhagen
Citation: Study challenges the hypothesis that higher oxygen levels led to the rise of multicellular organisms in Earth’s oceans (2023, July 18) retrieved on July 18, 2023 from https://phys.org/ news/2023-07-assumption-higher-oxygen-multicellular- yuta.html
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