Two billion years is an extremely long length of time for humanity, but that seems to be the end of the line for Earth, as predicted by astrobiologists at the University of East Anglia, UK.
Andrew Rushby and his team of scientists have recently developed a “hybrid habitable zone model” which includes facets of an older, “classical habitable zone model,” updated to include information about star development and expanded to include conditions elsewhere in the universe. The habitable zone model, in either form, posits that life typically evolves within a certain set of conditions where a planet is within a narrow band close enough to a star to avoid freezing solid and developing into a gas giant, but far enough away that the planet’s liquid water doesn’t evaporate away. Thanks to the hybrid model, Rushby’s team can expand knowledge of the classical model as it applies to earth to other stellar conditions.
Rushby’s model advances the classical model by incorporating knowledge about how stars in general, rather than just Sol, our sun, change over time. Using the model, Earth will move out of the habitable zone by moving closer to the “hot zone” of the sun, where the heat will boil off liquid water into steam and gas, causing a drastic change in conditions that results in mass extinction of terrestrial organisms.
However, despite the foreboding implications of the model, two billion years is a vast length of time for sapient life. That said, Rushby believes that given the vast development time for evolution to occur to the point where intelligent life emerges, it is likely that a planet needs to be in a star’s habitable zone for at least a billion years for intelligent life to evolve. Even if humanity doesn’t last for the rest of Earth’s lifetime, there’s a chance that another intelligent species could take our place if we went extinct.
In the event that some other event doesn’t wipe us out first, or we don’t develop the technology to colonize other worlds, a good alternative to Earth is probably our planetary neighbor, Mars. While Earth will last another 1.75 billion years, Rushby’s model predicts that Mars will remain in the habitable zone for the next six billion years, until the sun itself dies.
While mankind is presently alone in the solar system, based on the habitable zone model, we may only have to wait another billion or two years for other life to appear. But a billion years is a long, long time and we have our work cut out for us.