Ancient Rocks Reveal Life on Earth Flourished a Billion Years Earlier Than Originally Thought

Life may have flourished on Earth far earlier than anyone expected. Scientists have taken a closer look at some of our planets oldest rocks and have found that 3.2 billion years ago, life already pulling nitrogen out of the air and converting it into a form that could support larger communities.

The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared just 2 billion years ago. This latest study, though, reveals that it occurred far earlier.

"People always had the idea that the really ancient biosphere was just tenuously clinging on to this inhospitable planet, and it wasn't until the emergence of nitrogen fixation that suddenly the biosphere became large and robust and diverse," said Roger Buick, co-author of the new study, in a news release. "Our work shows that there was no nitrogen crisis on the early Earth, and therefore it could have supported a fairly large and diverse biosphere."

In order to get a better sense of ancient Earth, the researchers 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.

So what did they find? The oldest sample at 3.2 billion years old showed chemical evidence that life was pulling nitrogen out of the air.

"Imagining that this really complicated process is so old, and has operated in the same way for 3.2 billion years, I think is fascinating," said Eva Stueken, lead author of the new study. "It suggests that these really complicated enzymes apparently formed really early, so maybe it's not so difficult for these enzymes to evolve."

The findings reveal that nitrogen-fixing enzymes occurred about a billion years early than expected. This may be further evidence that some early life may have existed in single-celled layers of land, exhaling small amounts of oxygen that reacted with the rock to release molybdenum in the water.

"We'll never find any direct evidence of land scum one cell thick, but this might be giving us indirect evidence that the land was inhabited," said Buick. "Microbes could have crawled out of the ocean and lived in a slime layer on the rocks on land, even before 3.2 billion years ago."

The findings are published in the journal Nature.

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