A timeline for evolution of metabolism in early microbes

Metabolism in early microbes evolved in three waves, beginning >3.4 Ga with fermentation and sulfur compound respiration, then ~3.2 Ga and ~1.4 Ga with later specializations.

• Why it matters: Uncertainty about when major metabolic pathways emerged and which microbes performed them limits how well we can connect microbial evolution to Earth’s changing chemistry.
• What they did: The study integrated machine learning, metabolic network modeling, and microbe phylogenomics to date 14 metabolism forms and 6 other traits, then compared predictions with geochemical dates.
• The result: Predicted timings matched conservative geochemical estimates well (CCC = 0.81 to 0.89) and also dated metabolism forms not visible in the geochemical record.

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