For now, Earth is a thriving oasis of life, wrapped in an atmosphere rich in oxygen.
But what if this life-giving gas were to disappear?
It may sound like the plot of a science fiction thriller, but scientists predict that in the distant future, Earth’s atmosphere will undergo a drastic transformation, reverting to a state similar to its prehistoric past—low in oxygen and dominated by methane.
And when that happens, most life as we know it will cease to exist.
The unsettling part? This transition will happen suddenly, at least on a geological timescale.
According to a 2021 study published in Nature Geoscience, the oxygen collapse will precede Earth’s transformation into a greenhouse world, wiping out oxygen-breathing organisms before the planet loses its surface water.
Researchers warn that our planet’s oxygen-rich phase is not a permanent feature of habitability.
This raises profound implications—not just for Earth’s distant future but for our search for alien life.
If oxygen is not a reliable biosignature, are we even looking for extraterrestrial life in the right way?
The Clock is Ticking—But Slowly
Before panic sets in, let’s put things into perspective. This doomsday scenario won’t unfold for about a billion years.
But when it does, it will occur within a relatively short period—perhaps just 10,000 years, a blink of an eye in geological terms.
This dramatic shift will take Earth back to conditions similar to those before the Great Oxidation Event (GOE) about 2.4 billion years ago.
Back then, Earth’s atmosphere had little oxygen, and anaerobic life forms—organisms that don’t need oxygen—were the dominant players. Once oxygen disappears again, such microbes will reclaim their reign.
“For many years, the lifespan of Earth’s biosphere has been discussed based on scientific knowledge about the steadily brightening of the Sun and global carbonate-silicate geochemical cycle,” said Kazumi Ozaki, an environmental scientist from Toho University in Japan, who co-authored the study.
In other words, as the Sun continues to brighten, it will trigger processes that strip the atmosphere of carbon dioxide.
This, in turn, will lead to a collapse in oxygen production.
A Future Without Oxygen—The Science Behind the Prediction
To arrive at their conclusions, scientists ran detailed simulations of Earth’s biosphere, incorporating factors such as the Sun’s increasing brightness and declining atmospheric carbon dioxide levels.
Their findings suggest that oxygen depletion will happen first—long before the planet’s oceans evaporate due to solar radiation.
“The model projects that a deoxygenation of the atmosphere, with atmospheric O₂ dropping sharply to levels reminiscent of the Archaean Earth, will most probably be triggered before the inception of moist greenhouse conditions in Earth’s climate system and before the extensive loss of surface water from the atmosphere,” the researchers explained.
In simpler terms, our planet will lose its breathable atmosphere before it becomes an uninhabitable fireball.
That means humans and most other oxygen-dependent creatures will vanish long before Earth itself becomes completely lifeless.
A Temporary Guest on Habitable Planets?
Here’s where things take a surprising turn. We tend to think of oxygen as a permanent and defining characteristic of habitable planets.
But this study suggests otherwise—oxygen may be just a temporary phase in a planet’s life cycle.
Chris Reinhard, an Earth scientist from the Georgia Institute of Technology, emphasized the dramatic nature of this shift:
“The drop in oxygen is very, very extreme. We’re talking around a million times less oxygen than there is today.”
This realization forces scientists to rethink how we search for alien life.
If oxygen-rich atmospheres are fleeting, then relying on oxygen as a primary biosignature might be a mistake.
A New Perspective
As astronomers develop increasingly powerful telescopes, they are gathering massive amounts of data on distant exoplanets.
But if Earth itself will one day lack oxygen, perhaps alien worlds that seem inhospitable today could, at different points in their histories, have supported life.
This research was conducted as part of NASA’s NExSS (Nexus for Exoplanet System Science) project, which aims to refine our understanding of planetary habitability.
The findings suggest that instead of just searching for oxygen, scientists might need to look for other biosignatures—such as methane or hydrogen sulfide—that could indicate the presence of life.
A World of Anaerobic Life Forms
According to the study, after Earth’s oxygen-rich era ends, the atmosphere will be methane-heavy, low in carbon dioxide, and devoid of an ozone layer.
The dominant life forms will be anaerobic microorganisms, similar to those that thrived on early Earth before oxygenation changed the game.
“The Earth system will probably be a world of anaerobic life forms,” said Ozaki.
It’s a sobering thought: one day, the very element that makes complex life possible—oxygen—will fade away.
And while microbial life may persist, humans and most other creatures will be long gone.
Can Humanity Escape Earth Before It’s Too Late?
The big question is: Will humanity find a way to leave Earth before this catastrophic shift happens?
While a billion years is a long time, the fact that Earth’s oxygen supply is ultimately temporary might serve as a powerful motivator for interstellar exploration.
If we hope to preserve the future of complex life, we may need to become a spacefaring civilization—long before Earth’s atmosphere turns against us.
For now, Earth is still a paradise for oxygen-breathing life.
But this research serves as a reminder that nothing in nature is permanent, not even the very air we breathe.
