Scientists from East China Normal University and Shenzhen University have unveiled a mystery surrounding the origin of complex life on Earth. Their study, published in Nature, reveals that the last common ancestor of all eukaryotes—organisms with a cell nucleus, including animals, plants, and fungi—existed around 2.72 billion years ago in an environment devoid of oxygen. This discovery overturns previous assumptions about the early stages of life’s evolution.

Life Without Oxygen

It was previously believed that the development of eukaryotes was closely tied to rising oxygen levels in Earth’s atmosphere, particularly after the Great Oxidation Event around 2.4 billion years ago. However, the new study demonstrates that eukaryotic ancestors emerged long before this event and were adapted to an oxygen-free environment. This suggests that complex life forms began to take shape in conditions previously considered unsuitable for their development.

The Origin of Eukaryotes

Scientists propose that eukaryotes evolved from ancient archaea, specifically the Asgard archaea, with Heimdallarchaeia as their closest relatives. A pivotal moment in evolution was the emergence of a symbiotic relationship between a hydrogen-dependent archaeon and a hydrogen-producing bacterium. This symbiosis likely laid the foundation for eukaryogenesis—the process of forming nucleated cells that became the basis for all complex organisms.

Significance for Science

The discovery reshapes our understanding of life’s evolution on Earth, showing that complex organisms could arise in conditions drastically different from those today. It also opens new avenues for studying the early stages of life’s development and enhances our understanding of how key biological processes were formed.

Search for Extraterrestrial Life

The study’s findings are relevant not only for Earth but also for the search for life in space. Scientists suggest that multicellular organisms could evolve in oxygen-free environments on other planets or moons, such as Europa or Enceladus. This broadens the criteria for seeking extraterrestrial life, pointing to the possibility of complex forms existing in environments previously deemed unsuitable.

Conclusion

The discovery by Chinese scientists sheds light on one of the most enigmatic stages of evolution—the emergence of complex life on Earth. The common ancestor of eukaryotes, living 2.72 billion years ago without oxygen, transforms our understanding of the planet’s history and opens new horizons for research. This breakthrough not only deepens our knowledge of earthly life but also inspires scientists to search for traces of complex organisms in the distant reaches of the cosmos.