For How Much Longer Can Life Continue on This Troubled Planet?

Wikipedia’s “Timeline of the Far Future” is one of my favorite webpages from the internet’s pre-slop era. A Londoner named Nick Webb created it on the morning of December 22, 2010. “Certain events in the future of the universe can be predicted with a comfortable level of accuracy,” he wrote at the top of the page. He then proposed a chronological list of 33 such events, beginning with the joining of Asia and Australia 40 million years from now. He noted that around this same time, Mars’s moon Phobos would complete its slow death spiral into the red planet’s surface. A community of 1,533 editors have since expanded the timeline to 160 events, including the heat death of the universe. I like to imagine these people on laptops in living rooms and cafés across the world, compiling obscure bits of speculative science into a secular Book of Revelation.

Like the best sci-fi world building, the Timeline of the Far Future can give you a key bump of the sublime. It reminds you that even the sturdiest-seeming features of our world are ephemeral, that in 1,100 years, Earth’s axis will point to a new North Star. In 250,000 years, an undersea volcano will pop up in the Pacific, adding an extra island to Hawaii. In the 1 million years that the Great Pyramid will take to erode, the sun will travel only about 1/200th of its orbit around the Milky Way, but in doing so, it will move into a new field of stars. Our current constellations will go all wobbly in the sky and then vanish.

Some aspects of the timeline are more certain than others. We know that most animals will look different 10 million years from now. We know that the continents will slowly drift together to form a new Pangaea. Africa will slam into Eurasia, sealing off the Mediterranean basin and raising a new Himalaya-like range across France, Italy, and Spain. In 400 million years, Saturn will have lost its rings. Earth will have replenished its fossil fuels. Our planet will also likely have sustained at least one mass-extinction-triggering impact, unless its inhabitants have learned to divert asteroids.

The events farther down the page tend to be shakier. Recently, there has been some dispute over the approximate date that complex life will no longer be able to live on Earth. Astrophysicists have long understood that in roughly half a billion years, the natural swelling of our sun will accelerate. The extra radiation that it pours into Earth’s atmosphere will widen the planet’s daily swing between hot and cold. Continents will expand and contract more violently, making the land brittle, and setting into motion a process that is far less spectacular than an asteroid strike but much deadlier. Rainfall will bring carbon dioxide down to the surface, where it will bond with the silicates exposed by cracking earth. Rivers will carry the resulting carbonate compounds to the ocean, where they will sink. About 1 billion years from now, this process will have transferred so much carbon dioxide to the seafloor that very little will remain in the air. Photosynthesis will be impossible. Forests and grasslands will have vanished. A few plants will make a valiant last stand, but then they, too, will suffocate, wrecking the food chain. Animals on land will go first; deep-sea invertebrates will be last. Microbes may survive for another billion years, but the era of complex life on Earth will have ended.

Researchers from the University of Chicago and Israel’s Weizmann Institute of Science have now proposed an update to this crucial part of the timeline. In a new paper called “Substantial Extension of the Lifetime of the Terrestrial Biosphere,” available as a preprint and accepted for publication in The Planetary Science Journal, they argue that the effects of silicate weathering may be overstated. In a billion years, they say, enough carbon dioxide may yet remain for plants to perform photosynthesis. That doesn’t mean plants will last forever. Even if they can continue breathing, the sheer heat of the ballooning sun will eventually kill them and every other living thing on Earth. The question is when, and the researchers note that there is reason for optimism on this score. Some plant species have already evolved to withstand extreme heat. (One flowering shrub in Death Valley appears to thrive at 117 degrees Fahrenheit.) In the future, they could evolve to withstand higher temperatures still. With carbon-dioxide starvation out of the picture, these hardy plants could perhaps live for 800 million extra years.

[Read: Scientists found ripples in space and time. And you have to buy groceries.]

Claims like these are laughably hard to test, of course. But in this case, there could be a way. Astronomers plan to use the next generation of space telescopes to zoom into the atmospheres of the nearest hundred Earthlike planets, looking for precise chemical combinations that indicate the presence of life. With this census, they hope to tell us whether life is common in the universe. If it is, and if humans keep on building bigger and bigger telescopes, then the astronomers of the 22nd century may be able to survey lots of planets at once, including those that orbit suns that are more swollen than ours. If in the atmospheres of these planets—these future Earth analogues—we see the telltale exhalations of photosynthesis, that could suggest that plantlike lifeforms here are indeed more resilient than we’d once imagined.

Until then, we will just have to keep tabs on the Timeline of the Far Future. Yesterday morning, I visited it again and scrolled down a billion years to see if it had been updated. It had not. I kept scrolling anyway, to remind myself how it all turns out. (Doomscrolling in its purest form.) I went 3, 4, and 5 billion years into the future, by which time the Milky Way will have merged with the Andromeda galaxy. Together, the two will gobble up all the other galaxies in our local, gravitationally bound group. Because the universe is expanding, everything beyond this consolidated mega-galaxy will recede away, leaving it to float alone like an island in a void. The longest-lasting of its stars will shine reddish-orange for trillions of years. Eventually, they’ll twinkle out, and only a black hole will remain. It, too, will evaporate, but over a period of time so long that expressing it in years is comical. The number runs for hundreds of digits.

It is a strange thing that humans do, calculating these expiration dates, not just for life but for stars and black holes. Scientists have even tried to determine when every last fizzing bit of energy in the cosmos will come to rest. We have no obvious stake in these predictions, and at a moment when there are more pressing reasons to doomscroll, they might rightly be called a distraction. I have no straightforward counterargument, only a vague suspicion that there is something ennobling in trying to hold the immensities of space and time inside our small and fragile mammal brains.