SEATTLE, Feb. 17 (UPI) — The left end of the evolutionary timeline may need to be extended quite a ways, as scientists contend life on Earth may have begun 1 billion years earlier than previously thought. The new hypothesis comes after researchers confirmed that the elements necessary for a burgeoning biosphere was in place earlier than once believed.
Even more so than oxygen, life needs nitrogen. Previously, researchers believed the atmosphere of infant Earth was thin and fickle, devoid of the nitrogen levels needed by early life forms — viruses, bacteria and all other microscopic organisms.
But new analysis of ancient rock samples reveal chemical evidence that early life forms were pulling nitrogen from the atmosphere as early as 3.2 billion years ago.
“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,” study co-author Roger Buick, a professor of Earth and space sciences at the University of Washington, said in a recent press 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.”
Among 52 rock samples, ranging in age from 2.75 billion to 3.2 billion years old, researchers found the chemical footprints of nitrogen-fixing enzymes that enable single-celled organisms to build and maintain complex gene sequences. The footprints reveal that the earliest organisms preferred molybdenum, one of the three most common nitrogen-fixing enzymes in the environment.
It’s evidence, researcher say, that microbial life likely stretched out across oceanside rocks in a thin film. And it’s the best evidence scientists can expect to find, Buick and his colleagues say.
“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,” Buick said. “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 new study was published Tuesday in the journal Nature.
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