Is our sun in the earth's atmosphere

The earth will lose its oxygen

Suffocating future: In around a billion years, the earth's atmosphere could have lost almost all of its oxygen - of the around 20 percent today, less than one percent remains, according to researchers. The reason for this is the natural aging of the sun and the associated increase in its radiation. This will change geochemical cycles and drastically thin out the flora, according to the scientists in the specialist magazine "Nature Geoscience".

The end is inevitable: because our sun changes in the course of its life cycle, the days of earthly life are also numbered. The luminosity of our star is already gradually increasing; in around a billion years it will emit around ten percent more radiation than it does today.

But this has consequences for the earth: The increased radiation and increased temperatures promote the weathering and binding of carbon dioxide (CO2) in the rock. As a result, the plants lack this gas for photosynthesis. As a result, the terrestrial vegetation will begin to dwindle in around 600 million years, as models suggest.

Fast forward to the future of the earth

But what does this mean for the oxygen in the earth's atmosphere? Kazumi Ozaki from Toho University in Japan and Christopher Reinhard from the Georgia Institute of Technology have now investigated this question in a NASA project. To do this, they expanded existing earth system and climate models to include the factors that influence the gas composition of the atmosphere, including weathering and geochemical material cycles, vegetation, but also solar radiation.

In a first test, they ran different versions of this combination model until they were able to correctly reconstruct the past development of the earth and its atmosphere. “The simulations of this ensemble group were then continued into the future in order to determine the lifespan of the earth's oxygen atmosphere,” the researchers explain. During this forecast run, they exposed their model earth to the increase in radiation that is predicted for solar development.

Drastic oxygen depletion in a billion years

The result: "In the long term, the oxygen content of the atmosphere will decrease substantially," report Ozaki and Reinhard. Specifically, the simulations showed that the earth's gas envelope will have less than one percent of its current oxygen content in 1.08 billion years. A large part of today's life forms could no longer exist under these conditions.

While oxygen and carbon dioxide decrease sharply, the proportion of methane in the earth's gas envelope will increase significantly during this time. “In many respects, the earth's atmosphere in the distant future will be similar to that of the primordial earth before the so-called Great Oxidation Event,” the researchers explain. This event around 2.4 billion years ago enriched the primordial atmosphere, which was previously dominated by methane, nitrogen and carbon dioxide, with oxygen in a short time.

Viewed from space, our planet could look more like the veiled Saturn moon Titan than a blue planet in a billion years: "According to forecasts, an increased methane content results in the formation of organic haze veils," said Ozaki and Reinhard.

Changed biogeochemical cycles as the main cause

But what is the cause of the dramatic loss of oxygen in the future earth's atmosphere? As the scientists report, the increasing solar radiation is the main driving force behind this. If they left them out in their models, there was no loss of oxygen. More detailed analyzes showed that the increased irradiation intensified weathering processes and increased temperatures. This in turn changes biogeochemical material cycles.

“Our analysis suggests that oceanic redox chemistry in particular can be decisive for the long-term development of the atmosphere on habitable planets,” the researchers write. The interaction between the sea, the earth's crust and the mantle regulates the flows of carbon, sulfur, phosphorus and iron and they all have an impact on the binding and release of oxygen through chemical and biological processes.

Meaning for the search for extraterrestrial life

"Our results suggest that an oxygen atmosphere is not a permanent condition even on life-friendly worlds with photosynthesis," state Ozaki and Reinhard. "Overall, only a fraction of the earth's history will be characterized by robustly detectable levels of atmospheric oxygen." This oxygen-rich phase only accounts for around 20 to 30 percent of the life of our earth.

This is also relevant for astrobiology and the search for life in space. Because oxygen is one of the most important biosignatures for life on foreign planets. But if this phase only lasts for a comparatively short time and then gives way to a methane-rich, veiled gas envelope, then such an atmosphere could at least point to earlier life, according to the researchers. (Nature Geoscience, 2021; doi: 10.1038 / s41561-021-00693-5)

Source: Nature Geoscience

March 2, 2021

- Nadja Podbregar