How Long Earth Oxygen Will Sustain? (Planetary Science)

Ozaki and Reinhard in their recent paper, examined the timescale of oxygen-rich atmosphere on Earth by using a combined biogeochemistry and climate model. They found that Earth will lose its oxygen-rich atmosphere in 1. 08 ± 0.14 billion years (which is appx. 1 billion years). Their paper recently appeared in Journal Nature Geoscience.

They showed that future deoxygenation is an inevitable consequence of increasing solar fluxes, whereas its precise timing is modulated by the exchange flux of reducing power between the mantle and the ocean-atmosphere-crust system.

Fig. 1. Schematic model structure. Boxes denote reservoirs, whereas arrows denote flux terms. The model tracks the major reservoirs and transfer fluxes within the surface carbon (C), sulphur (S), oxygen (O), and phosphorus (P) cycles, along with a comprehensive treatment of ocean biogeochemistry, and long-term transfers between the crust-ocean-atmosphere system and the mantle. DOA = degree of anoxia.

That is, around 1 billion years from now on, sun will grew hotter, releasing more energy, carbon dioxide levels in Earth’s atmosphere will begin to drop due to the gas absorbing the heat and breaking down. The ozone layer would also be burned away. Then, as carbon dioxide levels fall, plant life will begin to suffer, resulting in reduced production of oxygen.

Over a period of just 10,000, years, CO2 levels will drop so much that plant life would go extinct. Without plant life, land- and sea-dwelling creatures would soon go extinct, as well, due to the lack of a breathable atmosphere. Meanwhile, the model results also showed increasing levels of methane entering the atmosphere, speeding the demise of creatures needing oxygen to breathe. The result, according to the model, would be a planet without life, save for tiny anaerobic creatures such as bacteria—conditions very similar to Earth prior to the evolution of plants and animals.

But, it is also important to note that there are multiple biogeochemical and climate processes that are not considered in their model that may play a role in constraining the future lifespan of Earth’s biosphere and the timing/mode of transition to more reducing atmospheric conditions. In particular, “reverse weathering” (the formation of authigenic silicates in marine sediments, resulting in net CO2 release to the ocean-atmosphere system) could potentially extend the lifespan of oxygenated atmospheric conditions under certain scenarios by prolonging the timescale over which atmospheric CO2 is above the levels expected to result in CO2 limitation of the photosynthetic biosphere.

In addition, they also hypothesized that haze-induced climate cooling could potentially act as a brake on the overall magnitude of atmospheric deoxygenation, or result in the inception of oxygenation/deoxygenation cycles during Earth’s terminal habitability.

Their results have important implications for the search for life on Earth-like planets beyond our solar system (e.g., habitable planets with abundant liquid water at the surface, exposed silicate crust, and a biosphere with oxygenic photosynthesis). According to authors, there is a need for robust atmospheric biosignatures applicable to weakly oxygenated and anoxic exoplanet atmospheres.

Reference: Ozaki, K., Reinhard, C.T. The future lifespan of Earth’s oxygenated atmosphere. Nat. Geosci. (2021).

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