More than a century ago, the sun seemed more dull than today, but the earth remained warm thanks to a strong greenhouse effect, says geoscience. Astronomer Carl Sagan conceived this as the "Faint Young Sun Paradox" and for decades researchers have been looking for the right balance of atmospheric gases that could have kept the Earth comfortable at an early stage.
A new study led by the Georgia Institute of Technology suggests that nitric oxide, known for its use as dental sedative nitrous oxide, may have played an important role.
The research team conducted experiments and atmospheric computer modeling that detailed an existing hypothesis about the presence of nitric oxide (N2O), a powerful greenhouse gas, in the old atmosphere. Established research has already pointed to high levels of carbon dioxide and methane, but they may not be plentiful enough to keep the bulb warm enough without the help of N2O.
Jennifer Glass, an assistant professor at Georgia Tech, and Chloe Stanton, formerly a research assistant at the Georgia Tech Glass lab, published the study in the journal Geobiology the week of August 20, 2018. Their work was funded by the NASA Astrobiology Institute. Stanton is now a graduate research assistant at Pennsylvania State University.
No & # 39; boring billion & # 39;
The study concentrated more than a billion years ago on the middle of the Proterozoic Eon. The proliferation of a complex life was still a few hundred million years old and the pace of the evolution of our planet probably seemed deceptively slow.
"People in our field often refer to this middle chapter in the history of the earth, about 1.8 to 0.8 billion years ago, as the" boring billion "because we regard it classically as a very stable period," Stanton said. , the first author of the study. "But there were many important processes that influenced ocean and atmospheric chemistry during this time."
Chemistry in the middle Proterozoic ocean was strongly influenced by abundant soluble ferrous iron (Fe2 +) in oxygen-free deep waters.
Old iron key
"The ocean chemistry was completely different then," said Glass, the principal investigator of the study. "Today's oceans are well oxygenated, so iron quickly rusts and falls out of the solution Oxygen was low in Proterozoic oceans, so they were filled with ferrous iron, which is very reactive."
In laboratory experiments, Stanton discovered that Fe2 + in seawater reacts quickly with nitrogen molecules, especially nitrogen monoxide, to produce nitric oxide in a process called chemo-nitrification. This nitrous oxide (N.2O) can then bubble up into the atmosphere.
When Stanton stopped the higher fluxes of nitrous oxide in the atmospheric model, the results showed that nitric oxide had reached ten times the current level when the mid-proterozoic oxygen concentrations were 10 percent of today's. This higher nitrogen oxide would have given an extra boost to the greenhouse effect under the Faint Young Sun.
Laughing laughing gas
Laughing gas could also have been what an old life breathed.
Even today, some microbes can breathe laughing gas when the oxygen is low. There are many similarities between the enzymes that microbes use to breathe in nitrogen and nitrogen oxides and enzymes that are used to breathe in oxygen. Previous studies have suggested that the latter has evolved from the previous two.
The Georgia Tech model provides an abundant source of nitric oxide in the ancient iron-rich seas for this evolutionary scenario. And prior to the Proterozoic, when oxygen was extremely low, early water microbes could already breathe in nitrogen oxide.
"It is quite possible that life breathes laughing gas long before it started to breathe oxygen," Glass said. "Chemo nitrification may have provided microbes with a solid source of energy."
The article was co-authored by Chris Reinhard of Georgia Tech, James Kasting of Pennsylvania State University, Nathaniel Ostrom and Joshua Haslun of Michigan State University, and Timothy Lyons of the Riverside of California University. The research was funded by NNA15BB03A grant from the NASA Astrobiology Institute. Findings, opinions and conclusions are those of the authors and not necessarily of the NASA Astrobiology program.
Material delivered by Georgia Institute of Technology. Note: content can be edited for style and length.