According to a news release from the University of Manchester, a new study has deepened the mystery of the origins of life on Earth. A team of researchers from the CRPG-CNRS University of Lorraine, The University of Manchester and the Institut de Physique du Globe de Paris have debunked a theory as to why the Earth was warm enough to keep up the Earth’s earliest life forms when the Sun’s energy was approximately 75 percent the strength it is today.

According to researchers, life developed on our planet during the Archean, between 3.8 and 2.4 billion years ago, but the less-powerful Sun should have signified that the Earth was too cold for life to develop at this point in time; thus researchers have been attempting to come up with a reason for this puzzle, known as the “faint, young Sun paradox.”

“During the Archean the solar energy received at the surface of the Earth was about 20 to 25 % lower than present,” said study author Ray Burgess, from the University of Manchester’s School of Earth, Atmospheric and Environmental Sciences. “If the greenhouse gas composition of the atmosphere was comparable to current levels then the Earth should have been permanently glaciated but geological evidence suggests there were no global glaciations before the end of the Archean and that liquid water was widespread.”

One explanation for the paradox was that greenhouse gas levels were much higher during the Archean than they are today.

“To counter the effect of the weaker Sun, carbon dioxide concentrations in the Earth’s atmosphere would need to have been 1,000 times higher than present,” said lead author Bernard Marty, a professor at the CRPG-CNRS University of Lorraine. “However, ancient fossil soils – the best indicators of ancient carbon dioxide levels in the atmosphere – suggest only modest levels during the Archean. Other atmospheric greenhouse gases were also present, in particular ammonia and methane, but these gases are fragile and easily destroyed by ultraviolet solar radiation, so are unlikely to have had any effect.”

The team chose to test another climate-warming theory. They wanted to determine whether the quantity of nitrogen could have been greater in the ancient atmosphere, which would increase the greenhouse impact of carbon dioxide and permit the planet to stay ice-free.

The researchers looked at small samples of air caught in water bubbles in quartz from a region of northern Australia that has very old and unusually well-preserved rocks.

“We measured the amount and isotopic abundances of nitrogen and argon in the ancient air,” Marty posited. “Argon is a noble gas which, being chemically inert, is an ideal element to monitor atmospheric change. Using the nitrogen and argon measurements we were able to reconstruct the amount and isotope composition of the nitrogen dissolved in the water and, from that, the atmosphere that was once in equilibrium with the water.”

The team discovered that the partial pressure of nitrogen in the Archean atmosphere was very much alike, may even a little bit lower, than it is at present, excluding nitrogen as one of the primary competitors for answering the early climate mystery.

“The amount of nitrogen in the atmosphere was too low to enhance the greenhouse effect of carbon dioxide sufficiently to warm the planet,” Burgess said. “However, our results did give a higher than expected pressure reading for carbon dioxide – at odds with the estimates based on fossil soils – which could be high enough to counteract the effects of the faint young Sun and will require further investigation.”

The study’s findings are described in greater detail in the journal Science.

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