There’s a new date for when life flourished on our planet. Research from the University of Washington has found evidence that 3.2 billion years ago, life was pulling nitrogen from Earth’s air and “converting it into a form that could support larger communities,” according to a University press release.
3.2 billion years ago, oxygen was absent in our atmosphere. Life can exist without oxygen, but it needs lots of nitrogen.
“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,” said co-author Roger Buick, a UW professor of Earth and space sciences. “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.”
What Exactly Was This ‘Work?’
The researchers looked at 52 samples ranging from 2.75 to 3.2 billion years old. These rock samples were collected in South Africa and northwestern Australia. They are some of the best preserved rocks on Earth and were formed from sediment deposited on continental margins. That means they are free from any chemical irregularities researchers might see near a subsea volcano.
The rocks also formed before our atmosphere gained oxygen, which is believed to have happened around 2.3 to 2.4 billion years ago.
The samples, including the oldest ones, showed chemical evidence that life was pulling nitrogen from the air. According to the press release:
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.
Previous analysis of nitrogen-fixing enzymes showed they originated between 1.5 and 2.2 billion years ago.
“This is hard evidence that pushes it back a further billion years,” Buick said.
These data cannot readily be explained by abiotic processes and therefore suggest biological nitrogen fixation, most probably using molybdenum-based nitrogenase as opposed to other variants that impart significant negative fractionations. Our data place a minimum age constraint of 3.2 billion years on the origin of biological nitrogen fixation and suggest that molybdenum was bioavailable in the mid-Archaean ocean long before the Great Oxidation Event.
Image credit: University of Washington/Roger Buick. Image shows rocks in northwestern Australia.