For all of our hand-wringing over the impending end of the world (a tradition that stretches back thousands of years) it’s easy to forget that one day that end is actually going to come. For real. Doom will be brought on not by an ancient calendar, or by the appearance of four men on horseback, or even, likely, by the firing of the world’s collective nuclear stockpile. If nothing else gets us, then the Earth will meet its end a few billion years from now when the Sun expands and burns us to a crisp.
But what fate besets those last hardy survivors, the life that clings on throughout the final days of the apocalypse? In Astrobiology Magazine, Amanda Doyle explores the likely paths tread by the last vestiges of terrestrial life.
As the Sun expands and the temperature soars, the evaporation of the oceans “will probably put a stop to plate tectonics,” since water is needed to lubricate the process, some scientists think, grinding the planet’s overturning surface to a halt.
With plate tectonics frozen, many volcanoes will begin to shut down, cutting off that supply of carbon dioxide to the atmosphere. No carbon means no photosynthesis, which means no growing plants. One way or another, it seems, a waterless world does not make for happy living.
The death of oxygen-producing plants will in turn lead to less oxygen in the atmosphere over a few million years. This will spell disaster for the remaining animal life on Earth, with mammals and birds being the first to become extinct. Fish, amphibians and reptiles would survive a little longer, as they need less oxygen and have a greater tolerance to heat.
The last animal holdouts, says Doyle, “would likely be invertebrates. Once the insects finally succumb to the increasing temperatures, the Earth will once again be solely populated by microbial life, just as it had been for the first few billion years of our planet’s history.”
Even these microbes, though, will not be able to hold on forever. First they’ll thrive in the steadily-shrinking oceans, then in the pools at the base of the trenches that currently cut through the sea floor. Microbes could hold out in ice caves, too. Or, deep beneath the surface of the Earth.
If humans manage to make it this far into the future, we would likely be baked off alongside the rest of the mammals. Our best bet for survival, brought to light by recent research, may be on one of the new planets discovered around the star Tau Ceti, the nearest single-star solar system to our own. Astronomers recently identified that Tau Ceti has five planets, one of which is in the habitable zone, the temperature band where liquid water can persist.