Newly discovered microfossils from Western Australia shed light on the sudden increase in complex life that accompanied the atmospheric and oceanic oxygen rise in the Great Oxidation Event.
What Happened During the Great Oxidation Event?
The Great Oxidation Event is a time interval during the early Paleoproterozoic Era, about 2.4 billion years ago, characterized by increased oxygen concentration on Earth. Also known as the Oxygen Revolution, this event fundamentally changed the surface of our planet.
These changes led to the formation of an ozone layer in the upper atmosphere, protecting against the Sun's harmful ultraviolet radiation. As a result, early lifeforms were allowed to expand from aquatic habitats into terrestrial environments.
Such development and the growing availability of oxygen in the atmosphere have led to the evolution of complex organisms. Aerobic respiration, which depends on oxygen, produces energy far more efficiently than anaerobic respiration. Therefore, the increase in oxygen level made it possible for multicellular organisms to evolve.
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Rise of Complex Lifeforms
A team of paleontologists examined exceptionally preserved, large spherical microfossils permineralized in an ancient Turee Creek Group in Western Australia. The rock containing the fossil was discovered by research corresponding author Erica Barlow while conducting her undergraduate research at the University of New South Wales (UNSW) in Australia.
The fossils are remarkably well preserved, which allowed for the combined study of their complexity, composition, and morphology. The researchers believe their research could better understand the changing biospheres billions of years ago.
The researchers analyzed the microfossils' chemical makeup and carbon isotopic composition and confirmed that living organisms created the carbon, indicating that the structures were biological fossils. They also unveiled insights into the microorganisms' habitat, metabolism, and reproduction.
The researchers compared the microfossils to modern organisms and found that they resemble a type of algae more closely than simpler prokaryotic organisms that existed before the Great Oxidation Event. Like other plants and animals, algae are eukaryotes with more complex life whose cells contain a membrane-bound nucleus. Compared to organisms from before the Great Oxidation Event, the microfossils were more extensive and featured more complex cellular patterns.
More work is needed to confirm if eukaryotic organisms left behind the microfossils, but the possibility would have significant implications. It would push back the known microfossil record by 750 million years. There is also a remarkable similarity between the microfossils and the modern family of Volvocaceae, hinting that the fossil could be an early eukaryotic fossil.
The result of the study shows the first direct evidence that connects the changing environment during the Great Oxidation Event with an increase in the complexity of lifeforms. The findings provide insight into how long it took for complex life to form on young Earth. It can also help search for life in other regions of the Solar System.
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