The Final Breath: How Earth's Oxygen Supply Will Eventually Run Out

 

As climate concerns dominate today's headlines, a recent projection by planetary scientists, including collaborators with NASA, has reignited an even more existential question: will Earth ever completely run out of oxygen? The sobering answer is yes—though not tomorrow, or even in the next few thousand years. According to cutting-edge climate-biosphere modeling, Earth’s breathable atmosphere may only have about 1 billion years left before oxygen becomes a rare commodity once again, spelling the end for most life as we know it.

A Billion-Year Clock Is Ticking

Researchers at NASA and affiliated institutions have used geochemical and climate models to forecast the distant future of Earth’s atmosphere. Their findings, recently published in peer-reviewed journals, point to a tipping point roughly 1.08 billion years from now when atmospheric oxygen will collapse rapidly.

This oxygen loss won’t be the result of pollution, deforestation, or human negligence—though those issues certainly threaten oxygen levels in the short term. Instead, it’s driven by the natural evolution of the Sun, whose increasing brightness will disrupt the delicate balance of Earth’s atmospheric chemistry.

As the Sun ages, its energy output increases. That extra heat will significantly alter Earth’s climate system, leading to accelerated weathering of silicate rocks—a process that consumes carbon dioxide. As CO₂ levels decline, photosynthesizing organisms like plants and phytoplankton will struggle to survive, causing oxygen production to plummet.

Why Losing CO₂ Means Losing O₂

Oxygen doesn’t just "exist" in our atmosphere. It’s constantly being replenished by photosynthetic life forms that convert CO₂ and water into sugars, releasing oxygen as a byproduct. But this process is highly dependent on the availability of carbon dioxide.

When CO₂ levels fall below a critical threshold—likely less than 10 parts per million—photosynthesis shuts down. Without plants and phytoplankton photosynthesizing, Earth loses its oxygen generation capacity.

The result? A sudden and dramatic drop in oxygen levels. Within about 10,000 years of the tipping point, oxygen concentrations could fall to levels not seen since the Archaean eon—over 2.4 billion years ago, long before complex life evolved.

What Happens to Life?

Such a shift would devastate most current lifeforms. Oxygen-breathing organisms—including humans, animals, and even many microbes—would die off. The atmosphere would revert to a methane-rich composition similar to early Earth’s, potentially bringing with it a thick orange haze and a dramatic cooling of the surface.

Some microbes and anaerobic bacteria may survive in isolated pockets, such as deep-sea vents or underground aquifers, where oxygen has never played a major role. But multicellular life would effectively be wiped out.

This event marks a true planetary extinction, one that dwarfs even the worst mass extinctions in Earth's history.

Will Human Activity Speed This Up?

Interestingly, while this scenario unfolds on billion-year time scales, it’s worth considering how human activity affects oxygen in the short term.

Today, oxygen levels are decreasing slightly due to fossil fuel combustion, which consumes O₂ and releases CO₂. However, this decline is currently measured in parts per million per year—a rate too small to pose a direct threat within any foreseeable future.

That said, human-driven climate change and ocean warming are accelerating ocean deoxygenation, a process already affecting marine life. Warmer water holds less oxygen, and the increased stratification of the oceans prevents the mixing that brings oxygen to deeper layers. Entire ecosystems are already experiencing oxygen stress, which could have long-term implications for Earth’s biosphere.

Still, none of these short-term processes come close to the catastrophic oxygen loss predicted in the far future due to solar evolution. The billion-year countdown remains on course, regardless of what humans do now.

How Scientists Know This

This prediction is based on advanced biogeochemical models that simulate how Earth’s climate, atmosphere, and life forms will interact as the Sun becomes more luminous. The models integrate factors such as volcanic activity, solar radiation, ocean chemistry, and biological feedback loops.

In one particularly influential study led by Kazumi Ozaki of Toho University in Japan and Christopher Reinhard of Georgia Tech—supported by NASA astrobiology research—scientists found that Earth’s oxygen-rich atmosphere is only a transient phase in its long history.

Earth has existed for about 4.5 billion years, but it has only had abundant oxygen for the last 2.4 billion. In a billion years, that phase will likely end, completing the cycle.

Implications Beyond Earth

Interestingly, this discovery has implications for the search for extraterrestrial life. Many exoplanet-hunting missions look for oxygen as a biosignature—a sign that a planet may host life.

But if oxygen only exists for a limited window of a planet’s life, we may be missing signs of life on worlds that are either too young or too old to have breathable atmospheres. This could force astronomers to refine their strategies and consider a wider range of biosignatures, including methane, ozone, or even chlorophyll-like pigments.

Should We Worry?

On human timescales, this event is unimaginably distant. Civilizations rise and fall over centuries—not eons. But the idea that Earth’s oxygen is not eternal reshapes how we view our planet and its fragility.

For now, our focus must remain on preserving the delicate oxygen-carbon balance that sustains life today. While the Sun's aging is inevitable, our stewardship of Earth’s biosphere is not. We still have agency—and responsibility—in the short term.