Washington, Feb 17:
After analysing ancient rocks, researchers now believe that life could have flourished on Earth 3.2 billion years ago, pushing the origin of life on Earth back a further billion years.
A team from the University of Washington has found evidence that 3.2 billion years ago, life was already pulling nitrogen out of 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 roughly two billion years ago.
“People always had the idea that the really ancient biosphere was just tenuously clinging on to this inhospitable planet and it was not until the emergence of nitrogen fixation that suddenly the biosphere become large and robust and diverse,” explained study co-author Roger Buick, professor of earth and space sciences.
The findings show that there was no nitrogen crisis on the early Earth and, therefore, it could have supported a fairly large and diverse biosphere, he added.
For the results, the team analysed 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.
Even the oldest samples, 3.2 billion years old, showed chemical evidence that life was pulling nitrogen out of air.
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.
“This is hard evidence that pushes it back a further billion years,” Buick said.
The authors’ hypothesis that this may be further evidence that some early life may have existed in single-celled layers on land.
“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 authors noted.
The results were published in the journal Nature. IANS