Eukaryogenesis and oxygen in Earth history

Area of Science:

• Origin of life
• Eukaryogenesis
• Biogeochemistry

Background:

• The endosymbiotic origin of mitochondria is traditionally linked to Earth's oxygenation.
• This view presumes an aerobic lifestyle for bacterial ancestors of mitochondria.
• Recent findings challenge this oxygen-centric perspective.

Purpose of the Study:

• To re-evaluate the environmental conditions and metabolic drivers of early eukaryogenesis and mitochondrial origin.
• To investigate the timing of eukaryogenesis relative to planetary redox transitions.

Main Methods:

• Analysis of fossil and molecular clock data.
• Integration of recent advances in Earth and life sciences.
• Consideration of metabolic evidence from Asgard archaea.

Main Results:

• Mitochondria-bearing eukaryotes predate the permanent rise of atmospheric oxygen and deep-sea anoxia.
• Eukaryogenesis is linked to anoxic deep-sea environments.
• Metabolic evidence suggests syntrophic H2 exchange between archaea and alpha-proteobacteria under anoxia.

Conclusions:

• The earliest stages of eukaryogenesis and mitochondrial origin are decoupled from surface oxygen levels.
• Obligate aerobiosis in eukaryotes is likely a derived trait, not ancestral.
• Early eukaryogenesis occurred in anoxic environments, challenging traditional views.