Scientists uncover oxygen-loving ancestor of all complex life
Science Daily
February 20, 2026
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Scientists have made a groundbreaking discovery that sheds light on how complex life on Earth evolved. For decades, researchers believed that complex life arose when two very different microbes merged—one requiring oxygen and the other thriving in oxygen-free environments. However, a major puzzle remained: how could these organisms meet if their survival needs seemed incompatible? New research suggests the answer lies in ancient microbes called Asgard archaea, which are close relatives of the ancestors of plants, animals, and fungi.
The study, published in *Nature*, reveals that some Asgard archaea can tolerate or even utilize oxygen, despite most known species being found in low-oxygen environments like deep-sea sediments. This finding supports the long-standing theory that complex life evolved in an environment where oxygen was present. Brett Baker, a marine science and integrative biology professor at The University of Texas at Austin, explained that the Asgards most closely related to eukaryotes are found in oxygen-rich habitats such as shallow coastal areas and can perform metabolic processes that rely on oxygen.
The research aligns with geological evidence of Earth's early atmosphere. Around 1.7 billion years ago, oxygen levels were extremely low, but during the Great Oxidation Event, oxygen concentrations rose sharply. This coincided with the appearance of the earliest known eukaryotic microfossils in the fossil record, suggesting a direct link between the availability of oxygen and the emergence of complex life. The study indicates that Asgard archaea adapted to this environmental change, gaining an energetic advantage by using oxygen, which eventually led to their evolution into eukaryotes.
The prevailing model for the origin of eukaryotes involves an Asgard archaeon forming a symbiotic relationship with an
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Originally published on Science Daily on 2/20/2026