Catastrophic Oxygen Decline: How It Could Threaten Every Life Form on Earth

Earth’s rich supply of oxygen makes life possible. But this wasn’t always the case. In fact, scientists believe that in about a billion years, our atmosphere will shift back to a methane-rich state with little to no oxygen.

No need to panic just yet—this big change is a long way off. When it happens, it could be swift, as highlighted in 2021 research. This would move our planet back in time to conditions similar to those before the Great Oxidation Event, which occurred around 2.4 billion years ago.

Kazumi Ozaki, an environmental scientist from Toho University, explains that as the sun grows brighter, carbon dioxide levels will steadily drop. This process indicates that oxygen in the atmosphere might not always be a given, which could affect our quest to find extraterrestrial life.

The study’s predictions suggest a sharp decline in atmospheric oxygen. According to their models, this would likely happen before a wet greenhouse effect takes over, and even before significant water loss from the atmosphere occurs. Without oxygen, most life forms, including humans, wouldn’t survive.

To arrive at these conclusions, researchers used complex models that incorporated changes in the sun’s brightness and how it affects carbon dioxide. Over time, decreased CO2 would reduce the number of plants, leading to less oxygen.

In the past, other scientists have warned that increased solar radiation could evaporate Earth’s oceans within two billion years. However, this new study suggests that reduced oxygen will be the first major threat to life.

Earth scientist Chris Reinhard from Georgia Tech noted that we’re looking at oxygen levels plunging to about one-millionth of what they are now. That’s an extreme drop!

This research is especially important today as scientists use powerful telescopes to search for habitable planets beyond our solar system. They need to identify what signs to look for. Oxygen might not be the go-to biosignature anymore. Instead, they might need to consider other indicators of life, especially as they analyze the data gathered from NASA’s NExSS (Nexus for Exoplanet System Science) project.

Interestingly, while Earth’s current biosphere may only last for 20-30% of its overall lifespan, tiny microbes will continue to exist long after we’re gone. Ozaki points out that after the oxygen levels drop, the atmosphere will be high in methane and low in carbon dioxide, leading to a world dominated by anaerobic life forms.

This study serves as a reminder of our planet’s dynamic environment and the necessity of understanding how life evolves in different conditions. You can read more about this research in the journal Nature Geoscience.

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