How much longer will the Earth be able to sustain life? Assuming our little blue marble isn't done in by climate change, an asteroid strike, or some other cataclysm, the end could come within 2 billion years.
"We estimate that Earth will cease to be habitable somewhere between 1.75 and 3.25 billion years from now," Andrew Rushby, a doctoral student at England's University of East Anglia and the lead author of a new study, said in a written statement. "Of course, conditions for humans and other complex life will become impossible much sooner -- and this is being accelerated by anthropogenic climate change."
What will happen by then to make life impossible on our planet? According to the researchers, intense heat from our aging sun will trigger runaway evaporation of water from Earth's oceans.
"Once this begins, an irreversible feedback takes place where high temperatures lead to more evaporation which leads to more humidity which leads to higher temperatures and more evaporation, etc.," Rushby told The Huffington Post in an email.
Of course, continued burning of fossil fuels and other causes of climate change could extinguish life a lot sooner than that. In a 2010 study, researchers at Purdue University and Australia's University of New South Wales found that climate change could make some areas of the Earth uninhabitable as early as 2300.
Rushby said the main focus of his research was to find a way to measure the potential habitability of Earthlike planets outside our solar system. To do this, the researchers estimated how the "habitable zone" around a star changes as the star evolves and how long a planet can remain habitable. As the timeline of evolution on Earth shows, complex life takes a long time to develop, so life-supporting planets probably required a lengthy habitable lifetime, Rushby told HuffPost Science.
"We found that some of the exoplanets in our study had long habitable lifetimes, similar to the Earth," Rushby said. "But one in particular, called Gliese 581d, had an extremely long habitable lifetime –- approximately 40 billion years in total! It’s about 8 billion years into this total now, so I think this would be a very interesting planet for future study."
Closer to home, the researchers determined that Mars would be the "best bet" if humans ever seek a new place to live. One of our closest neighbors -- only Venus is closer -- Mars will remain in the habitable zone until our Sun dies in 6 billion years.
"Mars would be a great place to watch the Sun go through its death throes," Rushby told Wired.
More information on the East Anglia research can be found in the researchers' new paper, "Habitable Zone Lifetimes of Exoplanets around Main Sequence Stars," published last week in the journal Astrobiology.