Can a buried time capsule beat Earth’s geology and deep time?NEWS | 26 January 2026This article is part of a package in collaboration with Forbes on time capsules, preserving information and communicating with the future. Read more from the report.
Stuff is old where I live, in greater Boston. Clapboard houses that list with age bear plaques touting the former residence of the town cordwainer or victualler. The gravestones, worn rough by New England winters, also stand crooked, bearing similarly outmoded biblical names—a Lemuel here, an Ephraim there. Old, too, are the local churches where many of these souls were commended to the great hereafter.
As for the building material that makes up these churches, well, that’s a little bit older still. Roxbury puddingstone, the mottled rock quarried nearby and used for much of the old church masonry in Boston, formed 600 million years ago in violent submarine landslides off the coast of a barren volcanic microcontinent that had been rifted off Africa. This upheaval happened so long ago in the course of the perpetual wandering of continents that the whole thing took place somewhere near the South Pole. The sediments hardened to rock, then hitched a ride across a bygone ocean as part of a traveling tectonic plate before being sutured onto the rest of equatorial North America some 140 million years before the first dinosaur evolved.
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This rock now pokes out from underneath fallen leaves and the edges of Dunkin’ parking lots in the Boston area. Very little else here has survived the intervening half-billion-year eon, save a superficial veneer of glacial till from the extremely recent last ice age—one that is surely doomed in the next few dozen millennia or so. Had somebody hoped to leave a time capsule for today’s Bostonians 250 million years ago in the Triassic period, or even four million years ago in the Pliocene epoch, they would have been completely, utterly screwed. The same is true for anyone aspiring today to send such an envoy into the geological deep future. Ephraim and Lemuel’s mortal remains, much less the local Dunkin’, will not survive into geological time. “Can any mountains, any continent, withstand such waste?” Charles Darwin wrote in his 1839 book The Voyage of the Beagle, referring to the defacing forces of erosion.
Mindful of my eon-old local rock and having been charged by Scientific American with figuring out how far into the deep future one could even hope to send a time capsule here on Earth, I stumbled on the humbling work of stratigrapher Steven Holland of the University of Georgia. I reached him at his office, and he gamely decided to play along with my thought experiment.
“Something like [five to 10 miles] of rock is gone above me right now,” Holland said, marveling at the vanished local mountains that should entomb his office deep within Earth. Their disappearance has much to tell us about the ravages of deep time. As Pangaea assembled from once disparate continents around 300 million years ago, the Maghreb, encompassing present-day northwestern Africa, headbutted the Eastern Seaboard, pushing the Appalachian Mountains high into the sky—American Himalayas that would have buried the Peach State. The collision injected giant blobs of magma deep into the crust—perhaps some 10 miles or so belowground. But today that old magma offers a granite face to the sunlight here, everything else on top having been completely eroded away in the meantime. “That just blows my mind,” Holland said.
Could we leave a time capsule for inhabitants of the next supercontinent to find 250 million years from now, just like we find fossils from Pangaea of 250 million years ago?
If we aspire to send a time capsule deep into the future, then Holland’s work is sobering. In one of his papers, a map of North America shows where sediments, and therefore fossils, have been preserved from across the entire 20-million-year-long Neogene period (23 million to 2.6 million years ago). Except for two tiny islands of preservation marooned in the middle of the continent and a fringing of old sediments along the coasts, it’s almost completely blank. “We have remnants of that sediment across the U.S.,” Holland says of the surviving islands of Neogene-age stuff in the middle of the country. “But even all those areas are uplifting,” or being pushed up by tectonic forces, and the unyielding work of erosion will most certainly plane them down. “So [the sediment is] a few tens of millions of years old, but it’s not going to last a whole lot longer.”
Making it into the very long-term fossil record requires getting buried by sediment, which, given enough time, becomes sedimentary rock. There are extraordinary quasi-exceptions to this rule: a rhino-shaped cave is etched into the basalts of the Pacific Northwest where an actual rhino was covered in lava 15 million years ago and left behind a cartoonish cavity of itself in the rock. But typically things don’t get preserved in lava. They get buried in stuff like muds, silts and clays, or they skip this step and make the rock themselves, as coral reefs do.
But burial isn’t nearly enough. For safe passage to the far future, you need to make sure you get interred in what’s called a sedimentary basin—a region that is sinking for larger, tectonic reasons, making space (“accommodation” in geology) that sediments can fill. A mastodon that gets buried in a swamp might last a few millennia in the dirt, but if that old sediment is part of a vast region that’s being subtly uplifted, then everything—and that means everything—will be lathed down to nothing by the forces of erosion.
Examples of this relentless demolition abound. The late, great Ancestral Rocky Mountains once stood where the current range does—and with equal grandeur—but were long ago worn as flat as a billiard table. If solid mountains in the wrong place have no chance of making it into the deep future, what chance would the hollow glass-and-steel façades of a human city have, much less our time capsule?
In those rare places where the crust is actively sinking—in the sagging flanks adjacent to new mountain chains or in the drooping, stretched, taffylike crust where a continent is trying to tear itself in half—sediments will fill the space above the slumping crust. These regions are where the fossil record begins. Unfortunately, today only 16 percent of Earth’s land surface is constituted of such sedimentary basins.
“The other place people might think to put a time capsule is at the bottom of the ocean, on the abyssal plains, right?” Holland said. They would be fools. Continental crust floats above the mantle essentially forever, but deep-ocean crust is far denser, so it gets continually fed to subduction zones at the edges of those ocean plates and destroyed. As a result, half the ocean floor is younger than 85 million years old. That sounds ancient, and it certainly is, but it’s still young enough to have missed out on the first 80 percent or so of the age of animal life (and more than 98 percent of the full history of Earth). If we want to leave a time capsule, say, for inhabitants of the next supercontinent to find 250 million years from now, just like we find fossils from the Pangaea of 250 million years ago, then the ocean floor is a terrible repository. “The oldest oceanic lithosphere we have is 180 million years old, and the fate of most oceanic lithosphere is to get subducted,” Holland said. “So if you put it down there, you’re going to get it for only 200 million years. And we are in it for the long haul here.”
Yet we do have a vast and vastly older fossil record of the oceans than any of the existing ocean crust on Earth today. Some of this rock is from pieces of deep ocean crust that occasionally got smudged onto the sides of the continents during collisions and outlived the rest of their plates. Far more commonly, though, it exists because the seas were draped high above the continental crust in the deep past, leaving a fossil record of ocean life in surprising places, like roadside outcrops in Kansas that spill shark teeth and the bones of giant seafaring reptiles. And in fact, we still have huge shallow seas sitting atop continental crust today. These waterlogged swaths of the continents are what’s known as the continental shelves—gently sloping extensions of the land that slink below the waves at the shoreline and then far out to sea before finally diving into the abyss. If it’s stupid to put our time capsule on the deep ocean floor, which gets continuously destroyed, what about these narrower perches just offshore?
A rough approximation of “Pangea Ultima” (250 million years in the future) based on maps by Christopher Scotese. Federico Tramonte
“You do have a couple of things to contend with if you’re putting stuff on the continental shelf,” said Hannah Sophia Davies, a postdoctoral researcher of tectonics and sedimentary systems at the Free University of Berlin, who was similarly intrigued by my bizarre assignment and agreed to play along. The climate is always changing, you might have heard. What this has meant in practice over the past few million years, as the planet has plunged into and out of extraordinary ice ages, is that there are equally extraordinary changes in sea level—from more than 400 feet lower than today at the depths of the glacial periods to perhaps more than 20 feet higher than now during temporary millennia-long breaks from the cold, like the one we’re currently in. The brief memory of recorded human history may lull us into an expectation of stable shorelines, but the seas have in fact oscillated wildly throughout the past. And wherever they pause, they begin to chew away at the landscape.
“As the sea level changes, it progressively cuts into the land, so that might kind of erode the material away where you’re trying to preserve the time capsule,” Davies said. This is a problem because the sea level is definitely going to change—first, perhaps, by rising dozens of feet in the geological short term as a result of human-caused warming. But eventually our carbon dioxide will be washed out of the system, and perhaps in 400,000 years we’ll fall into a new deep ice age. If so, the sea level will drop hundreds of feet, the shelves will once again be exposed to the bracing air, and erosion will reign.
What if we put our time capsule a little deeper, near the edges of the shelves, which always stay below sea level but remain precariously perched above the ocean crust? “I would think that’s not a particularly good idea,” Davies said, “because every now and again you have these massive submarine landslides called turbidity currents, and those transport all the material offshore into the deep ocean. So they will probably just destroy anything that you put there.”
Even worse, the Atlantic continental shelf and other so-called passive margins, which just sit there placidly collecting sediment, unmolested by tectonics, don’t stay passive forever. In 1755 a preposterously giant earthquake leveled Lisbon, killing tens of thousands of pious churchgoers—on All Saints’ Day, no less. The magnitude 8.7 tremor was awful enough that in the minds of some Enlightenment-era philosophers, it destroyed the idea of an all-powerful, kind and loving God. It might have also kick-started the destruction of the entire Atlantic Ocean. The event might have been the initial grumblings of a new subduction zone, a tectonic maw that will someday invade the Atlantic Ocean through the Strait of Gibraltar, chewing up ocean crust as it spreads. If so, it would only mirror its more mature counterparts across the Atlantic today: two crescents of deep ocean trench where the seafloor is similarly being fed to the mantle. For their part, these American subduction zones may infect the rest of the western Atlantic, effectively throwing into reverse a tectonic spreading system that has been successfully pushing the ocean apart for 180 million years. Ultimately, this action may swallow the entire Atlantic as the planet inaugurates its next supercontinent. Needless to say, this would probably be bad for the fragile sediments of today’s Atlantic continental shelf.
Every message needs a receiver, even if it’s just to puzzle over some baffling zircons hundreds of millions of years from now.
Elsewhere the immense submerged swath of shelf from Australia to Vietnam, which hosted countless stegodonts and, later, humans in the ice ages—and which now hosts their fossils deep underwater—is similarly slated for destruction. “Australia is going to collide with Southeast Asia, which will generate a huge mountain chain,” Davies said. “And that happens super quick, in, like, the next 30 million years.”
Returning to land, what about that 16 percent of continental crust that is home to sedimentary basins? Well, most of it is desert, which brings us to the next hurdle: taphonomy, or the process of fossilization itself. If one is extraordinarily lucky, the cliff walls of Navajo sandstone will occasionally reveal to them the permineralized bones of a hapless prosauropod, killed by a sand dune collapse in the Jurassic, but never in much detail. “Sand is really porous, so sandstones don’t preserve fine detail,” Holland said. “So, yeah, that would not be my favorite place to put something.”
By this point in my search, having eliminated most of the world, I was stumped. I’d learned that we want to put our capsule in a sedimentary basin, hermetically sealed off from the oxidative ravages of the surface world, but probably not in a desert and not in—or perhaps even near—the ocean. Looking at Holland’s map, I thought I had a breakthrough: bury it at the bottom of the Black Sea! After all, it’s in a sedimentary basin in the middle of a landmass, and it’s clearly anoxic—it even pickled the shipwrecks of Roman galleys in breathtaking detail. Nope. “That whole area—basically, as you go from the Himalayas through the Middle East, up through Turkey and into the Alps—is just a fright zone,” Holland said about the impossibly complex and ongoing crashing of Eurasia into Africa. “There’s so much collision that I think that whole area has really poor preservation potential. Like, the Mediterranean is going to be gone.”
Okay, fine. Where are we going to put this thing?
“I like the East African rift,” Holland said. “I would probably put it there.”
Some 200 million years ago, when the planet decided to break up Pangaea, the first attempts at tearing North America from Africa failed, leaving behind a necklace of deep, narrow rift-valley lakes from Massachusetts to South Carolina. Something similar may be underway now in East Africa, home to Lake Malawi and Lake Tanganyika. The ancient beds in North America still give up scaled fish fossils and lakeside crocodilian footprints as they erode from outcrops at the edges of parking lots in Newark or quarries just outside Washington Dulles International Airport. With this in mind, then, perhaps we should charter a pirogue out to the middle of Lake Malawi, drop our time capsule into its deepest, most anoxic waters, cross our fingers and hope for the best. Or maybe there’s something we can do to help the preservation process along.
We’ve avoided discussing so far what this thing should be made of. A metal canister might do for a couple of decades, but we need to be more selective as we reach deeper into the geological future. Metal corrodes; glass devitrifies. Even our infamous legacy of plastics won’t last long in the geological record: it will degrade into a strange residue of long-chain organic biomarkers. “Chemical weathering is the real killer,” Holland said. And chiseling something out of granite would be downright idiotic because the weathering and erosion of silicate rock such as granite is just about the most reliable thing that happens on our planet. “Minerals can be ranked in terms of their susceptibility to chemical weathering,” he said. “Something made of quartz is extremely resistant. And actually—I’m not sure how you get as much of it, but the most resistant thing I can think of is zircon.”
We still have nearly indestructible grains of zircon from the very dawn of Earth’s history, almost 4.4 billion years ago, even though nothing else has survived from the primeval world of the early Hadean eon. “We have zircons that are basically as old as Earth, right?” Holland said. “So if you could, if you wanted to make something that was going to basically last forever, I’d make it out of zircon.”
It’s no small irony that the very reason this exercise is near impossible is the reason we’re here in the first place.
When I described Holland’s East African rift idea to Davies, she was wary (fearing the capsule might meet an early grave at the bottom of a new East African Ocean), but the wheels began turning when I mentioned Holland’s zircon plan. “Oh, yeah, that’s good. You could, like, laser etch in zircon.... It would even stand a chance of surviving orogeny,” she said, referring to the titanic mountain-building collisions that mangle and cook lesser minerals. “So actually that’s an interesting discussion, then, because you don’t really need to find it in an outcrop. You could find it detritally.” In other words, you wouldn’t have to uncover the time capsule in the rocks where it was originally placed, which may erode away; instead you could find it wherever it ended up.
“If it eroded down a mountain and you dug it up at the coast before it got to the continental shelf or if it ended up buried in the ocean, maybe that would work,” Davies said, adding that it could be possible to build a zircon with a strange, unnatural isotope concentration that would signal its human-made origin. “If you’re just kind of screaming into the void, ‘We were here,’ then it would maybe make sense to distribute a lot of these weird zircons just to mess with future civilizations. But then, I guess, it depends on what the point of the time capsule is: Are you making a Voyager disc? Are you saying, ‘Here’s humanity. Here’s what we were’?”
This question leads to the final and perhaps most speculative part of an exercise that has long since veered into irresponsible speculation: someone has to find the damn thing. Every message needs a receiver, even if it’s just to puzzle over some baffling zircons hundreds of millions of years from now. This requirement probably eliminates the most obvious solution to all of the problems outlined so far: Simply find the most stable, interior part of a continent, far from any tectonic drama. Drill a mile-deep hole, put your time capsule in there, and seal it up with whatever—cement, maybe. And indeed, this approach would almost certainly work. There’s just one problem. “You can put the time capsule in a deep borehole in the middle of the planet and seal it up, but nobody’s ever going to find it,” Holland said.
To ensure our laser-etched, isotopically deranged block of zircon gets discovered in the future, it’s not enough for it to be committed for safekeeping in a subsiding sedimentary basin or even dropped into some fathomless shaft in the bedrock. After all, there are miles-thick stacks of strata positively loaded with fossils underneath our feet that no one will ever study because they’ll never see the light of day. To actually transmit our message, then, our rocks have to be subsequently uplifted at some point hundreds of millions of years from now just enough to be eroded and revealed at the surface. But then you’d have to be there at the exact right time to catch them before they’re inevitably eroded out of existence. And the prospect of being at the right place at the right time—in the window of a few decades or so—to look for this thing when it’s exposed on the surface somewhere in our several-hundred-million-year journey ... well, this is all getting a little silly.
Our knowledge of the far future of plate tectonics peters out somewhere around 250 million years from now, and even then it’s an understatement to call our grasp of this future geography sketchy. Nevertheless, every 400 million to 600 million years, it seems, all the continents tend to assemble into one hemisphere-spanning union called a supercontinent, with Pangaea being the most recent example. By applying what they know about plate tectonics and subduction zones and running a model forward as far as is reasonable (and then quite a bit further), several groups of geoscientists have tried their hand at projecting the next supercontinent’s configuration some 200 million to 250 million years in the future. Three of the groups predict that a behemoth will be huddled around the tropics (although the fact that one group has it forming over the North Pole gives some indication as to the level of guesswork involved). The canonical version, called Pangaea Ultima, was imagined by Northwestern University geologist Christopher Scotese.
Pangaea Ultima is virtually a reprise of the previous Pangaea: the Atlantic Ocean ultimately closes much in the manner described earlier, with the Americas and Africa reversing course and lazily drifting back toward each other before slowly, if violently, reuniting 250 million years from now. In this scenario, Davies had her eye on Namibia.
Namibia is a sedimentary standout today. And it’s unlikely to be disturbed by any major tectonic disruptions in the very long haul—until that happy day when it crashes into the Americas and gets uplifted as part of a lengthy mountain chain trending east-west at the very heart of the supercontinent, not unlike the Central Pangaean Mountains hundreds of millions of years before them.
Discouragingly, even if paleontologists exist in the world of Pangaea Ultima 250 million years from now, and even if we luck out on everything outlined so far, the rocks to which we entrust our capsule would have to end up on a part of the planet that these future paleontologists would be likely to study. It might seem like a strange quibble, but today our understanding of the history of life on Earth is hugely biased toward the fossil record of the Northern Hemisphere for very human reasons, up to and including the history of global economic development. And although speculating on the political economy of the next supercontinent might be even more ridiculous than musing about its tectonics, there are reasons to worry about the prospects of anyone—no matter where they come from on the tree of life—ever carrying out fieldwork across enormous swaths of Pangaea Ultima. That’s because except for its polar fringes, it will be an absolute hellhole.
Supercontinents are miserable places to begin with. The last Pangaea, for instance, featured an expansive, arid equatorial interior that was virtually devoid of life, brutally hot and streaked in toxic, superacidic salt playas. The interior of the next supercontinent is likely to be even worse because the sun will grow about 2.5 percent brighter by the age of Pangaea Ultima.
Paleoclimatologist Alexander Farnsworth of the University of Bristol in England and his colleagues have produced a menacing picture of the climate of this world. Daily temperatures could exceed an unthinkable 122 to 140 degrees Fahrenheit for months on end across the entire supercontinent. Mammals can’t survive sustained temperatures above 104 degrees F—a seemingly hard limit over our entire quarter-billion-year evolutionary history—and the components of photosynthesis break down at 104 to 140 degrees F. Unless future paleontologists restrict themselves to the polar fringes of Pangaea Ultima, they will die. “If the time capsule survives the continental collision, then maybe it would be exposed in your Central Pangaea Ultima Mountains,” Davies said. “But then, yeah, there’s the problem of getting at it when it’s 140 degrees out.”
Where does that leave us? If nothing else, this ridiculous thought experiment should drive home what a churning, restless planet we live on. This exercise would be trivially easy on Mars or the moon because those are dead, hopeless worlds. It’s not difficult on Mars to find river and lake sediments from four billion years ago exposed on the surface today. The moon still bears the fresh wounds of an asteroid impact 4.3 billion years ago. On Earth there aren’t even chunks of rock that old, and the Chicxulub crater, the biggest impact crater known to have formed in the past billion years, is hardly visible on the planet’s surface, buried under tens of millions of years’ worth of limestone and covered in jungle. If there were bigger impacts over that immense time span than the one that wiped out the dinosaurs, they’ve been all but erased.
That’s because our planet is alive. Plate tectonics ceaselessly reworks Earth’s surface: it pushes up mountains and creates and destroys oceans. Weather wears those same mountains down, and rivers carve canyons, seeding the oceans with nutrients that slough off the land and fuel life. This patient demolition helpfully draws CO 2 out of the air as well, maintaining a habitable temperature for complex life through the chemical alchemy of rock weathering and erosion, which transforms carbon in the air to limestone at the bottom of the ocean over hundreds of millennia. This sequestration of CO 2 is almost perfectly in balance with its contribution to the atmosphere elsewhere as it vents from volcanoes—volcanoes fired by subduction, rifting and all the other processes that ceaselessly remake our surface world. It’s a good deal for life on Earth. And it’s no small irony that the very reason this exercise is nearly impossible is the reason we’re here in the first place.
“I think it’s becoming more and more obvious to a lot of geologists that plate tectonics is necessary for the long-term habitability of a planet,” Davies said, considering the strange thought experiment I had recruited her into. “It’s almost an interesting kind of catch-22: you need plate tectonics to develop civilizations, but plate tectonics can quite easily just destroy any remnants of civilization on a planet.”Author: Seth Fletcher. Peter Brannen. Source
