The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago, researchers said.
Now research from the University of Washington looking at some of the planet's oldest rocks has found evidence that 3.2 billion years ago, life was already pulling nitrogen out of the air and converting it into a form that could support larger communities.
The authors analyzed 52 samples ranging in age from 2.75 to 3.2 billion years old, collected in South Africa and northwestern Australia. These are some of the oldest and best-preserved rocks on the planet.
The rocks were formed from sediment deposited on continental margins, so are free of chemical irregularities that would occur near a sub-sea volcano.
They also formed before the atmosphere gained oxygen, roughly 2.3 to 2.4 billion years ago, and so preserve chemical clues that have disappeared in modern rocks.
Even the oldest samples, 3.2 billion years old - three-quarters of the way back to the birth of the planet - showed chemical evidence that life was pulling nitrogen out of the air, researchers said.
The ratio of heavier to lighter nitrogen atoms fits the pattern of nitrogen-fixing enzymes contained in single-celled organisms, and does not match any chemical reactions that occur in the absence of life.
Genetic analysis of nitrogen-fixing enzymes have placed their origin at between 1.5 and 2.2 billion years ago.
Fixing nitrogen means breaking a tenacious triple bond that holds nitrogen atoms in pairs in the atmosphere and joining a single nitrogen to a molecule that is easier for living things to use.
The study was published in the journal Nature.

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