Life on Earth Emerged Earlier Than Previously Thought

Life on Earth supposedly first flourished about two billion years ago, but now a new analysis finds that living organisms actually emerged earlier than scientists previously thought.

According to conventional theories, either a spark from a lightning bolt, interstellar dust, or an underwater volcano triggered the very first life on Earth. But these events alone were not enough to sustain life. Atmospheric nitrogen was also a key ingredient.

Early life forms may have been able to live without oxygen - which didn't appear in our atmosphere until the "great oxidation event" some 2.3 billion years ago - but they needed nitrogen to build genes essential to viruses, bacteria and all other organisms.

This ability, according to the results reported in the journal Nature, arose around 3.2 billion years ago - about a billion years earlier than previous estimates suggested. Though the most basic forms of life are thought to have existed even earlier than the 3.2 billion mark, the new findings push back scientists' understanding of when life became widespread.

"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 become large and robust and diverse," co-author Roger Buick, from the University of Washington, said 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."

The new timescale is based on an analysis of some of Earth's oldest and best-preserved rocks in South Africa and northwestern Australia, dating back between 2.75 and 3.2 billion years ago. The researchers found that these 52 sedimentary samples contain chemical signatures of nitrogen fixation by microbes, which entails breaking the strong nitrogen triple bond and converting it into a usable form.

Non-biological processes such as a lightning strike or subsea volcanic eruption may have converted bonded atmospheric nitrogen in small amounts, but not enough to sustain large populations of living cells. The ancient rocks indicate that after such events, life was capable of pulling nitrogen out of the air as far back as 3.2 billion years ago and creting widespread life.

"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," added lead author Eva Stüeken. "It suggests that these really complicated enzymes apparently formed really early, so maybe it's not so difficult for these enzymes to evolve."

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