Our Sun is middle-aged, with about five billion years left in its lifespan. However, it’s expected to go through some changes as it gets older, as we all do — and these changes will affect our planet. New research published in Nature Geoscience shows that Earth’s oxygen will only stick around for another billion years.
One of the Sun's age-related changes is getting brighter as it gets older. When a star runs out of hydrogen fuel in its core, the core has to get hotter in order to fuse the next element, helium. As the core gets hotter, the outer layers expand, and the star gets brighter. This extra energy hitting Earth will eventually cause our planet to warm up and slowly lose its oceans and its oxygen.
The exact timing of when we lose our oxygen depends on more complicated factors — particularly our planet’s carbonate-silicate cycle, which releases carbon dioxide into the atmosphere from volcanoes. As the mantle cools and this cycle slows, less carbon dioxide will be available for the plants that produce oxygen, leading to a rapid loss of oxygen in the atmosphere. The researchers’ model took into account all these factors — our biosphere, the Sun’s changes, our planet’s changes, and more — to come up with their estimate of about a billion years.
Interestingly, this means that planets like Earth only have oxygen for a fraction of their lifetimes. When we try to find habitable worlds, this will be important to keep in mind.