Earth's atmosphere has an expiration date

 Earth's atmosphere has an expiration date

The gases surrounding our planet, rich in oxygen for nearly 2.4 billion years, have an expiration date, and the atmosphere will eventually run out of both CO2 and oxygen, new research on the lifespan of our protective layer has revealed.

From the atmosphere to the deep sea, Earth's various habitats are rich in oxygen. We now know with a fair amount of certainty that most of the oxygen in Earth's atmosphere comes from events that occurred sometime between 2.4 and 2.05 billion years ago, about 2.8 billion years ago, when oxygen-producing microbes called cyanobacteria are thought to have first appeared. 500 million years ago was the time of the so-called "Great Oxygen Holocaust," a brief period when, geologically speaking, the proliferation of these microorganisms generated large amounts of oxygen and transformed life on Earth.

The presence of oxygen is an anomaly in the Earth's geological history; in fact, the so-called oxygen crisis is now considered one of the greatest environmental catastrophes to have occurred on the planet. It is estimated that this catastrophe wiped out many species that once inhabited the planet, but it is thanks to this catastrophe that we are here.

We know where the oxygen we breathe comes from. However, its presence may be an anomaly in Earth's geological history, since oxygen was created by life forms that emerged during the Paleozoic era. This phenomenon is an important issue not only for life on Earth, but also for the search for life on similar planets outside our solar system.

A new study, "The future lifespan of Earth's oxygenated atmosphere," published in Nature Geoscience, addresses this question using a numerical model that combines biogeochemistry and climatology and shows that the future Demonstrates that the lifespan of Earth's oxygenated atmosphere is approximately one billion years.

Kazumi Ozaki, associate professor at Toho University, explains, "For many years, the lifetime of the Earth's biosphere has been debated based on knowledge of the solar and global carbonate-silicate geochemical cycles. The global carbonate-silicate cycle is one of the mechanisms that ensure that the Earth's average temperature remains in equilibrium within the range in which liquid water can exist. As the Earth's temperature rises, rocks erode, releasing the calcium trapped in them into the ocean, leading to the formation of limestone, which then combines with atmospheric CO2.

The Earth's biosphere is projected to come to an end within the next two billion years due to overheating and a lack of CO2 needed for photosynthesis.

Although it may seem counterintuitive at first glance, this gradual reduction of atmospheric CO2 over geological time scales will cause all CO2 to disappear from the Earth's atmosphere in the long term. The Earth's biosphere is expected to die out over the next two billion years as it overheats due to a lack of CO2 needed for photosynthesis." If that is the case," Ozaki continues, "the oxygen content of the atmosphere will also decrease in the distant future. But we don't yet know exactly when or how that will happen," Ozaki continues.

Ozaki and his Georgia Tech colleague Christopher Reinhardt have developed an Earth system model that combines climate and biogeochemical processes to study how the Earth's atmosphere might change in the future. Because modeling Earth's future evolution involves numerous geological and biological uncertainties, a stochastic approach was used to obtain a probabilistic estimate of the lifetime of the oxygen-rich atmosphere.

The atmosphere after the "Great Deoxygenation" would be characterized by high methane concentrations, low CO2 concentrations, and the absence of an ozone layer. The Earth system would likely become a world of anaerobic life forms," the researchers explain.

After running the model more than 400,000 times with different parameters, Ozaki predicts that today's oxygen-rich atmosphere will remain relatively stable for another billion years, until Earth's atmosphere more closely resembles that of the early Earth through a rapid deoxygenation event corresponding to the Great Oxidation Event about 2,400 years ago. "The atmosphere after the Great Oxidation Event is expected to be relatively stable for another billion years until it becomes more similar to the atmosphere of the early Earth. The atmosphere after the Great Oxidation Event will be characterized by high methane concentrations, low CO2 concentrations, and loss of the ozone layer. The Earth could become a world of anaerobic organisms," says Ozaki.

Earth's oxygen-rich atmosphere is an important sign of life that can be detected from a distance. However, this study suggests that it will not be a permanent feature of Earth, as the lifetime of Earth's oxygen-rich atmosphere is estimated to be about 20-30% of the time our planet is inhabited.

Oxygen and its photochemical byproduct, ozone, are the most widely accepted biological signals for the search for life on exoplanets. However, if Ozaki's findings are applied to Earth-like planets, scientists should consider other biological signals in their search for life on exoplanets, including planets with anoxic conditions or low oxygen concentrations.

BY Macbeth Avila