Eukaryotes flourished on a low-oxygen Earth

What is it about?

Complex life (eukaryotes) flourished comparatively late in the evolutionary history of life on Earth. Why? For decades, people suspected that low levels of atmospheric oxygen prevented early eukaryotes from reaching modern levels of diversity. However, we find that atmospheric oxygen would have needed to have been exceeding low -- less than 2-3% or modern levels -- to have significantly suppressed early microbial eukaryote diversity. Indeed, if these oxygen levels were met when the eukaryotic cell emerged, then oxygen availability did not suppress the diversity of the earliest microbial eukaryote ecosystems.

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Photo by Benjamin R. on Unsplash

Photo by Benjamin R. on Unsplash

Why is it important?

Determining the global environmental controls on biological evolution is essential to reconstructing the evolutionary history of life on Earth, and informs our search for inhabited worlds elsewhere in the observable universe. For example, if an exoplanetary atmosphere is ultimately found to contain only 2-3% of Earth's modern atmospheric oxygen inventory, then such a world could conceivably support a diversity of 'complex' microbes analogous to Earth's microbial eukaryotes. Alternatively, if an exoplanetary atmosphere is found to contain less oxygen, then such a world would be less hospitable to complex Earth-like life.

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