What the Earth might look like when the Sun enters its red giant phase, via Wikimedia Commons
Like any good mother, at some point the good Earth isn’t going to support us anymore. People—and indeed all life—is just a phase that the planet is going through, and like all phases, ours will come to an end. In human terms it’s far off, but in Earth terms...actually it still seems pretty far off.
Astrobiologists at the University of East Anglia have estimated that the Earth will sustain life for at least another 1.74 billion years, and maybe as long as 3.25 billion years from now. The researchers were able to estimate how long Earth will be in the Sun's "habitable zone," which is the distance from a star where liquid water could conceivably be found. Habitable zones vary based on the size and age of the star, which, as they age, grow hotter. The habitable zone around smaller stars can last for tens of billions of Earth years. The Earth gets to bask in the habitable zone for about 6.29 billion years, and three-fourths of that time has already passed.
“After this point, Earth will be in the ‘hot zone’ of the sun, with temperatures so high that the seas would evaporate,” said Andrew Rushby, a PhD student at UEA’s School of Environmental Sciences. “We would see a catastrophic and terminal extinction event for all life.”
Gosh, the image of the seas evaporating, leaving steaming hot whale corpses all over the place is grim, isn’t it? Fortunately, that’s not what’s going to happen—all the whales will be long dead by the time the oceans evaporate, so cheer up!
That conditional “we would see a catastophic and terminal extinction event” is due to the fact that Rushby is skeptical that life will even make it that long, for reasons that are both our fault, and also written into the solar system long before we ever emitted our first carbon breath into Earth’s lovely air.
“Of course conditions for humans and other complex life will become impossible much sooner,” said Rushby, “and this is being accelerated by anthropogenic climate change. Humans would be in trouble with even a small increase in temperature, and near the end only microbes in niche environments would be able to endure the heat.”
While it’s always fun to get a sober reminder of the futility of human endeavor, the astrobiologists were trying to do more than just cast a pall over your day. The study, published in the journal Astrobiology, was a look at how long planets occupy the habitable zone around other stars, and which ones are there long enough for life to evolve. Rushby said on his blog that estimating the Earth's finite time in the habitable zone was just part of the search for exoplanets that might also sustain life.
“Looking at habitability metrics is useful because it allows us to investigate the potential for other planets to host life, and understand the stage that life may be at elsewhere in the galaxy,” said Rushby. “Of course, much of evolution is down to luck, so this isn’t concrete, but we know that complex, intelligent species like humans could not emerge after only a few million years because it took us 75 per cent of the entire habitable lifetime of this planet to evolve. We think it will probably be a similar story elsewhere.”
Planets going around smaller stars occupy the habitable zone longer, but then there’s more to having life that simply being the right distance from a star. Both the Moon and our neighbor Mars are in the habitable zone, but scientists estimate that they don’t have the necessary atmospheres to sustain liquid water.
Still, if we’re around in a couple billion years and are still looking for a place, Mars is a solid option. According to Rushby, “it’s very close and will remain in the habitable zone until the end of the Sun’s lifetime - six billion years from now.”
So there you have it. Plan accordingly.