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Microfossils reveal a leap in life's complexity 2.4 billion years ago

In a recent groundbreaking study, scientists have uncovered microfossils in Western Australia that provide new insights into the Great Oxidation Event, a pivotal period in Earth’s history approximately 2.4 billion years ago when oxygen levels dramatically rose. 

This research, published in the journal Geobiology, offers rare evidence of how this increase in oxygen potentially led to more complex forms of life. The discovery is significant as it provides the first direct link between environmental changes during the Great Oxidation Event and an increase in life complexity.

Study significance 

Erica Barlow, the corresponding author and an affiliate research professor in the Department of Geosciences at Pennsylvania State University, expressed the importance of these findings. 

“What we show is the first direct evidence linking the changing environment during the Great Oxidation Event with an increase in the complexity of life,” said Barlow. “This is something that’s been hypothesized, but there’s just such little fossil record that we haven’t been able to test it.”

Leap in life’s complexity

The microfossils, which bear a closer resemblance to algae than to simpler prokaryotic life forms like bacteria, suggest a significant leap in life’s complexity. Algae, along with other plants and animals, belong to eukaryotes, a more complex form of life characterized by cells with a membrane-bound nucleus. 

While further research is needed to confirm if these microfossils indeed represent eukaryotic organisms, such a finding would be monumental, potentially pushing back the known eukaryotic microfossil record by 750 million years.

Focus of the research 

Barlow discovered the fossil-containing rock during her undergraduate research at the University of New South Wales (UNSW) in Australia. She continued this work during her doctoral studies at UNSW and as a postdoctoral researcher at Penn State. 

“The microfossils have a remarkable similarity to a modern family called Volvocaceae,” she explained. “This hints at the fossil being possibly an early eukaryotic fossil. That’s a big claim, and something that needs more work, but it raises an exciting question that the community can build on and test.”

Chemical analysis 

Co-author Christopher House, a professor of Geosciences at Penn State, highlighted the exceptional preservation of these fossils, enabling a detailed study of their morphology, composition, and complexity. 

The team’s chemical analysis confirmed the biological nature of these structures, offering insights into the habitat, reproduction, and metabolism of the microorganisms.

Burst of life

Barlow’s comparison of these samples to pre-Great Oxidation Event microfossils revealed significant differences, notably in size and cellular complexity. “The record seems to reveal a burst of life – there’s an increase in diversity and complexity of this fossilized life that we are finding,” she remarked.

Life beyond Earth

These findings not only shed light on the evolution of complex life on early Earth but also hint at the possibilities of discovering more complex life forms beyond our planet. Barlow reflected on this, suggesting that if life is found elsewhere, it might not be limited to simple bacterial forms. 

“Maybe there’s a chance there could be something more complex preserved – even if it’s still microscopic, it could be something of a slightly higher order,” she concluded.

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