Two scientists from Toho University and NASA’s Nexus for Exoplanet System Science ran computer simulations and found that Earth’s oxygen-rich atmosphere won’t last forever—it will start disappearing in about a billion years. In their study, published in Nature Geoscience, Kazumi Ozaki and Christopher Reinhard break down the details of their simulation and what it revealed.
Why won’t Earth support life forever?
Experts all agree on one thing: Earth won’t be home to life indefinitely. At some point, the sun will burn through its fuel and take the planet down with it. But well before that fiery finale, rising temperatures will make survival increasingly difficult. This study set out to figure out exactly when Earth will stop being a livable place for most plants and animals. Essentially, they wanted to pinpoint the moment when life runs out of breath —literally.
To figure out when Earth will no longer be a good place for most living things, the scientists built a computer model that mimicked the planet’s climate, along with geological and biological processes. The biggest piece of the puzzle? The sun’s behavior over time. They then let their simulation run to see how Earth would hold up in the distant future. Spoiler alert: it doesn’t end well for oxygen-breathing creatures.
The simulation predicted that in about a billion years, as the sun cranks up the heat and pours more energy onto Earth, carbon dioxide levels will start to drop. This happens because CO2 absorbs heat and eventually breaks apart. The ozone layer wouldn’t stand a chance either—it would get fried in the process.
What did the simulation reveal?
As CO2 levels plummet, plants would struggle to survive since they need that gas to make food. Within just 10,000 years —a blink of an eye in geological terms— plants would completely disappear. And without plants making oxygen, animals on land and in the ocean would follow suit, gasping their way to extinction.
To make matters worse, methane levels would start to rise, speeding up the downfall of oxygen-breathing creatures. When all is said and done, Earth would be left with nothing but tiny bacteria that don’t need oxygen to survive —pretty much the same kind of life that existed before plants and animals ever showed up. In other words, Earth would come full circle, back to its lonely, microbe-filled past.
The researchers behind the study estimate that Earth’s oxygen-rich atmosphere has about 1.08 billion years left before it starts running on empty. For some perspective, oxygen didn’t even begin to build up in the atmosphere until 2.5 billion years ago, during what’s known as the Great Oxidation Event. Even after that, oxygen levels likely remained low for most of Earth’s history, only reaching something close to today’s levels when land plants evolved roughly 400 million years ago.
What does this mean for the search for alien life?
The researchers estimate that Earth will remain habitable —meaning it will keep its surface water— for about 7.2 billion years in total. However, the stretch of time when the planet actually has an oxygen-rich atmosphere is much shorter, making up only about 20% to 30% of that period.
Why is this important?
Picture this: If we were aliens scanning the galaxy for life, we’d likely search for oxygen and ozone in the atmospheres of distant planets as clues that something is living there. But if our telescopes happened to focus on Earth 2 billion years ago—or 2 billion years into the future—we might not see those gases at all. That could lead us to mistakenly assume Earth was lifeless and move on, completely missing the window when it actually had breathable air. In other words, finding life may be all about catching planets at just the right moment—because even a thriving world can be having an “off day” in the grand scheme of time.
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