The Cambrian seas teemed with new types of animal, such as the predator Anomalocaris (centre).
Credit: John Sibbick
Natural History Museum
Natural History Museum
Biologists are changing their collective minds about how multicellular life arose on Earth, but it's nothing for creationists to get over-excited about. They aren't beginning to think it was all magicked by a magic man in the sky. The change of mind is about the exact mechanism and the trigger that started the evolutionary process. No objective biologist thinks the explanation is anything other than a natural, evolutionary process.
It used to be thought that the trigger for the evolution of multicellular organisms, which only evolved between 685 and 800 million years ago, was increasing levels of oxygen caused by the waste product of the photosynthesising cyanobacteria. They had been, like their descendant today in the chloroplasts of green plants, converting carbon dioxide and water into glucose and oxygen, and so polluting their own environment with their waste product - oxygen.
However, the idea that it was rising oxygen levels that triggered the change, has been disputed by the findings of a team from the University of Copenhagen, Denmark, Woods Hole Oceanographic Institute, Massachusetts, USA, the University of Southern Denmark, and Sultan Qaboos University, Muscat, Oman.
The team arrived at their conclusion after analysing the chemical composition of ancient rock samples from an Omani mountain range deposited during what geologists call the 'Shuram Formation produced during what is referred to as the 'Shuram carbon isotope excursion':
The Shuram ExcursionA news release from the University of Copenhagen explains the research and its significance:
The "Shuram excursion" refers to an important geological event known as the Shuram carbon isotope excursion. It is a term used in the field of geology to describe a dramatic shift in the carbon isotope composition of carbonate rocks that occurred around 635 million years ago during the Neoproterozoic era.
The Shuram excursion holds significance in the study of Earth's history and the evolution of life because it is closely associated with the emergence of complex multicellular organisms. During this time, Earth experienced a series of environmental changes, including extreme glaciations and the breakup of the supercontinent Rodinia. These environmental perturbations likely played a role in triggering the Shuram excursion.
The excursion itself is characterized by a significant negative shift in the ratio of carbon-13 to carbon-12 isotopes (δ13C) preserved in carbonate rocks. The negative excursion suggests a massive input of organic carbon into the ocean and atmosphere, which could have been caused by events like extensive organic matter burial, enhanced organic carbon cycling, or increased weathering of organic-rich rocks.
The Shuram excursion is intriguing to scientists because it provides insights into the complex interactions between Earth's geological processes and the evolution of life. The timing of this event corresponds with the rise of early complex multicellular organisms, including the Ediacaran biota, which represent some of the earliest evidence of large and morphologically complex life forms on Earth.
While the exact relationship between the Shuram excursion and the evolution of multicellularity is still a topic of ongoing research, it is believed that the environmental changes associated with the excursion, such as fluctuations in nutrient availability and oxygen levels, may have influenced the emergence and diversification of multicellular life during this critical period in Earth's history.
ChatGPT3 "What was the Shuram excursion and what is its significance to geology?" [Response to user question] Retrieved from https://chat.openai.com/
Between 685 and 800 million years ago, multicellular organisms began to appear in all of Earth's oceans during what's known as the Avalon explosion, a forerunner era of the more famed Cambrian explosion. During this era, sea sponges and other bizarre multicellular organisms replaced small single-celled amoeba, algae and bacteria, which until then, had had run of the planet for more than 2 billion years.The scientists' findings were published behind a paywall in the online journal Geobiology:
Up until now, it was believed that increased oxygen levels triggered the evolutionary arrival of more advanced marine organisms. This is being disproved by University of Copenhagen researchers working together with colleagues from Woods Hole Oceanographic Institute, the University of Southern Denmark and Lund University, among others.
By studying the chemical composition of ancient rock samples from an Omani mountain range, the researchers have been able to "measure" oxygen concentrations in the world's oceans from when these multicellular organisms appeared. Defying expectations, the result shows that Earth’s oxygen concentrations had not increased. Indeed, levels remained 5-10 times lower than today, which is roughly how much oxygen there is at twice the height of Mount Everest.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.
The fact that we now know, with a high degree of certainty, that oxygen didn’t control the development of life on Earth provides us with an entirely new story about how life arose and what factors controlled this success. Specifically, it means that we need to rethink a lot of the things that we believed to be true from our childhood learning. And textbooks need to be revised and rewritten.
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.
It’s interesting that the explosion of multicellular organisms occurs at a time with low concentrations of atmospheric and oceanic oxygen. That indicates that organisms benefited from lower levels of oxygen and were able to develop in peace, as the water chemistry protected their stem cells naturally.
We know that animals and humans must be able to maintain low concentrations of oxygen in order 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.
Associate Professor Christian J. Bjerrum, co-author
Department of Geoscience and Natural Resource Management
Nordic Center for Earth Evolution,
University of Copenhagen, Copenhagen K, Denmark.
[Associate professor Christian J. Bjerrum] has been quantifying the conditions surrounding the origin of life for the past 20 years.
Revises our understanding of life’s origins
The new result puts to rest a 70-year research story that advances the centrality of higher oxygen concentrations in the development of more advanced life on our planet.
There remains much that the researchers don't know, as well as and a [sic] plethora of controversy. Therefore, Bjerrum hopes that the new result can spur other researchers around the world to reconsider their previous results and data in a new light.
Fossils from Oman
In the new study, the researchers analysed rock samples from, among other places, the Oman Mountains in northern Oman. While quite high and very dry today, the mountains were on the seabed during the Avalon explosion’s rapid blossoming of organism diversity.
The researchers have had their findings confirmed in fossils from three different mountain ranges around the world: the Oman Mountains (Oman), Mackenzie Mountains (NW Canada) and the Yangtze Gorges area of South China.
Over time, clay and sand from land are washed into the sea, where they settle into layers on the seabed. By going down through these layers and examining their chemical composition, researchers can get a picture of ocean chemistry at a particular geologic time.
The analyses were performed using Thallium and Uranium isotopes found in the mountains, which the researchers were able to extract data from, and in doing so, calculate oxygen levels from many hundreds of millions of years ago.
Absence of oxygen may have aided development
So, if not extra oxygen, what triggered the era’s explosion of life? Perhaps the exact opposite. According to [Professor Christian J. Bjerrum], the same phenomenon has been studied in cancer research, in the stem cells of humans and other animals. Here, colleagues at Lund University observed that low oxygen levels are crucial for keeping stem cells under control until an organism decides that the cell ought to develop into a specific type of cell, such as a muscle cell.
AbstractThe interesting thing from a biological perspective is the suggestion that the differentiation into specialised cells in the earliest multicellular organisms in the Ediacaran biota could have had the same mechanism as that of the differentiation of stem cells in modern organisms, i.e., a lack of oxygen kept them undifferentiated until signal from the organism initiated the differentiation.
Reconstructing the oxygenation history of Earth's oceans during the Ediacaran period (635 to 539 million years ago) has been challenging, and this has led to a polarizing debate about the environmental conditions that played host to the rise of animals. One focal point of this debate is the largest negative inorganic C-isotope excursion recognized in the geologic record, the Shuram excursion, and whether this relic tracks the global-scale oxygenation of Earth's deep oceans. To help inform this debate, we conducted a detailed geochemical investigation of two siliciclastic-dominated successions from Oman deposited through the Shuram Formation. Iron speciation data from both successions indicate formation beneath an intermittently anoxic local water column. Authigenic thallium (Tl) isotopic compositions leached from both successions are indistinguishable from bulk upper continental crust (ε205TlA ≈ −2) and, by analogy with modern equivalents, likely representative of the ancient seawater ε205Tl value. A crustal seawater ε205Tl value requires limited manganese (Mn) oxide burial on the ancient seafloor, and by extension widely distributed anoxic sediment porewaters. This inference is supported by muted redox-sensitive element enrichments (V, Mo, and U) and consistent with some combination of widespread (a) bottom water anoxia and (b) high sedimentary organic matter loading. Contrary to a classical hypothesis, our interpretations place the Shuram excursion, and any coeval animal evolutionary events, in a predominantly anoxic global ocean.
Ostrander, C. M., Bjerrum, C. J., Ahm, A.-S. C., Stenger, S. R., Bergmann, K. D., El-Ghali, M. A. K., Harthi, A. R., Aisri, Z., & Nielsen, S. G. (2023).
Widespread seafloor anoxia during generation of the Ediacaran Shuram carbon isotope excursion. Geobiology, 00, 1–15. https://doi.org/10.1111/gbi.12557
© 2023 John Wiley & Sons, Inc.
Reprinted with Kind permission under licence #5602720446216
Whether or not this finding is subsequently confirmed, there is no comfort for creationists either in the fact that biologists might be wrong or in the fact that science changes its collective mind when new evidence demands it, because there is no hint of a suggestion that the scientists might be about to abandon the fundamental, overarching theory in biology - the Theory of Evolution. The debate is about the precise details and what the triggers were.
No serious biomedical scientist doubts that.
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