It has always been understood that Earth’s lifespan and its ability for supporting life is finite. According to scientists, Earth still has 1.75 billion years before it becomes uninhabitable, as long as it doesn’t get destroyed by an asteroid or we blow it up ourselves somehow.
So how did scientists come up with this number? They first looked at what defines a habitable zone in a solar system. Planets are considered habitable when they have liquid water, which is considered the keystone of life. Liquid water only forms on planets that sit within a certain zone around its star. As habitable zones change due to stars evolving over time, a planet can get pushed out of the zone. If it ends up too far away, its water becomes ice. If it’s pushed too close to the star, the water vaporizes.
As it stands now, Earth is sitting on the inner edge of the sun’s habitable zone. Scientists estimated that the current zone is moving outwards at about 1 meter per year. They developed a new model and figured out that Earth’s total amount of time in the zone is 6.3 billion to 7.8 billion years. If that’s the case, Earth is already about 70% through its life cycle as a habitable planet.
The research was more focused on the search for life on other planets, though. Scientists hope that in understanding how habitable zones work by looking at our own, they can easily pinpoint other planets out there similar to Earth and capable of sustaining life.