Microfossils discovered in Western Australia suggest a significant leap in the complexity of life during the Great Oxidation Event, hinting at the early evolution of complex organisms like algae.
Microfossils from Western Australia may reflect an increase in the complexity of life that coincided with increased oxygen in the Earth’s atmosphere and oceans, according to an international team of scientists.
The results, published in the journal Geobiology, provide a rare window into the Great Oxidation Event, a time around 2.4 billion years ago when the concentration of oxygen increased on Earth, fundamentally changing the planet’s surface. This event is thought to have triggered a mass extinction and opened the door for the development of more complex life, but little direct evidence existed in the fossil record before the discovery of the new microfossils, the scientists said.
First direct evidence linking environmental change and complex life
“What we show is the first direct evidence linking the changing environment during the Great Oxidation Event to an increase in the complexity of life,” said corresponding author Erica Barlow, an affiliated research professor in the Department of geosciences from Penn State. “It’s a hypothesis that has been put forward, but there are so few fossils that we haven’t been able to test it.”
Comparison with modern organisms and algae
Compared to modern organisms, the microfossils looked more like a type of algae than simpler prokaryotic life — organisms like bacteria, for example — that existed before the Great Oxidation Event, the scientists said. Algae, like all other plants and animals, are eukaryotes, a more complex life whose cells have a membrane-bound nucleus.
More work is needed to determine whether the microfossils were left behind by eukaryotic organisms, but the possibility would have significant implications, the scientists said. This would push back the known record of eukaryotic microfossils by 750 million years.
“The microfossils show remarkable similarity to a modern family called Volvocaceae,” Barlow said. “This suggests that the fossil could be a primitive eukaryotic fossil. This is a big claim and something that needs more work, but it raises an exciting question for the community to build on and test.
Barlow discovered the rock containing the fossils while conducting her undergraduate research at the University of New South Wales (USNW) in Australia. She carried out the current work as part of her doctoral work at UNSW and then while she was a postdoctoral researcher at Penn State.
Implications and future research
“These specific fossils are remarkably well preserved, which allowed the combined study of their morphology, composition and complexity,” said Christopher House, professor of geosciences at Penn State and co-author of the study. “The results open a large window into an evolving biosphere billions of years ago.”
The scientists analyzed the chemical composition and carbon isotopic composition of the microfossils and determined that the carbon was created by living organisms, confirming that the structures were indeed biological fossils. They also discovered information about the habitat, reproduction and metabolism of microorganisms.
Barlow compared the samples to microfossils from before the Great Oxidation Event and was unable to find any comparable organisms. The microfossils she found were larger and had more complex cellular arrangements, she said.
“The records appear to reveal an explosion of life – we are seeing an increase in the diversity and complexity of this fossilized life,” Barlow said.
Compared to modern organisms, Barlow said, microfossils show explicit similarities to algal colonies, including in the shape, size and distribution of the colony and individual cells and membranes around the cell and colony. .
“They have a remarkable similarity and so, by this method of comparison, we could say that these fossils were relatively complex,” Barlow said. “There’s nothing like it in the fossil record, and yet they have some pretty striking similarities to modern algae.”
Broader implications for understanding life on Earth and beyond
These findings have implications both for how long it took for complex life to form on the early Earth – the first uncontroversial evidence of life was 3.5 billion years ago – and what the search for life elsewhere in the solar system could reveal it, scientists said.
“I think finding such a large and complex fossil, relatively early in the history of life on Earth, makes us wonder: If we find life elsewhere, it might not just be of prokaryotic bacterial life,” Barlow said. . “There may be a chance that something more complex is preserved – even if it’s still microscopic, it could be something of a slightly higher order.”
Reference: “A distinctive microfossil supports early Paleoproterozoic uplift in a complex cellular organization” by Erica V. Barlow, Christopher H. House, Ming-Chang Liu, Maxwell T. Wetherington, and Martin J. Van Kranendonk, October 6, 2023, Geobiology.
Maxwell Wetherington, a scientist at Penn State, also contributed; Ming-Chang Liu, scientist at Lawrence Livermore National Laboratory; and Martin Van Kranendonk, professor at the University of New South Wales in Australia.
The Australian Research Council, NASA and the National Science Foundation funded this work.