LIFE × EVOLUTION

Life Pulls Nitrogen Out of the Air

at least 3.2 billion years ago

Archean · Mesoarchean

Four fifths of the air is nitrogen, but its two atoms are locked together so tightly that almost nothing alive can prise them apart. An enzyme called nitrogenase broke that lock, and turned the atmosphere itself into fertiliser. Rocks more than three billion years old carry its isotopic signature, and ancestral forms of the enzyme, resurrected in the laboratory, leave the same signature today. One puzzle remains: nitrogenase needs molybdenum, a metal that should have been scarce before there was oxygen to free it from rock, and yet the enzyme was already running.

Why it matters

Every protein and every strand of DNA needs nitrogen. This enzyme lifted the ceiling on how much life the planet could carry.

Dating & uncertainty

Nitrogen isotope ratios in rocks from 3.2 to 2.75 Ga sit where the enzyme nitrogenase would put them, which sets a minimum age rather than a date of origin. Resurrected ancestral enzymes reproduce the same signature, which supports reading the rocks this way.

Sources

1. Stüeken et al. (2015), Nature · Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr
2. Mus et al. (2019), Free Radical Biology and Medicine · Geobiological feedbacks, oxygen, and the evolution of nitrogenase
3. Rucker et al. (2026), Nature Communications · Resurrected nitrogenases recapitulate canonical N-isotope biosignatures over two billion years

Earth history as one day

07:05:0116 h 55 min before midnight

if Earth’s 4.54 billion years were compressed into a single day