Scientists have found clues in ancient rocks that suggest life on Earth became more complex at the same time oxygen levels increased in the atmosphere and oceans.

The rocks contain tiny fossils called microfossils that are over 2.4 billion years old. By studying these microfossils, researchers learned that complex life may have evolved earlier than we thought.

The microfossils were discovered in old rocky formations in Western Australia. When scientists looked closely at the fossils under microscopes, they saw that the ancient microbes resembled more advanced algae instead of the simpler bacteria and microbes that existed before oxygen levels rose. Algae, like plants and animals, have cells with nuclei – this makes them more complex than bacteria.

This is an important discovery because it shows that as Earth’s air and water began to contain more oxygen, life itself may have become more complex too. Scientists have thought this was possible, but didn’t have proof until now. These fossils provide direct evidence linking environmental changes to the evolution of more advanced microscopic life.

The fossils look a lot like modern algae groups called Volvocaceae. This suggests they were early complex cells called eukaryotes. Eukaryotes have nuclei and are more advanced than bacteria.

If confirmed, it would push back the earliest known complex fossils by over 750 million years. More research is needed, but it raises exciting questions about early life on our planet.

The researcher who found the rocks studied them for years as a student in Australia and recently as part of her work in the United States. The fossils are well-preserved, allowing scientists to learn about the ancient microbes by looking at their shape, what they were made of, and how their cells were arranged. Comparison to older fossils without oxygen showed these were more complex.

This discovery helps us better understand how long it took complex life to first evolve on Earth and could also help in the search for life elsewhere in our solar system.

Finding such early complex microbes suggests that if any other life is discovered, it may not just be simple bacteria—more intricate microscopic life is also possible. These ancient microfossils provide new clues about the major event that marked the rise of oxygen and complexity in life on our planet long ago.


The Pennsylvania State University | Barlow, E. V., House, C. H., Liu, M.-C., Wetherington, M. T., & Van Kranendonk, M. J. (2023). Distinctive microfossil supports early Paleoproterozoic rise in complex cellular organisation. Geobiology, 00, 1–23.

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