Works of Man that Would Last Millions of Years

So over in GQ, we’re on a bit of a tangent about ancient lost civilizations. We’re talking LOST over millions of years. Civilizations of the non-human variety. I’m positing that we’d know because of things that last a long time.

I’ve also gotten interested in things we’ve done that would show up in millions of years when the damn raccoons or something have evolved into an industrial civilization.

So put yourself in their little, bemasked feet, my friends. Imagine you’re looking for evidence of a non-raccoon civilization from 10+ million years ago. Would it be self-evident a la the predecessor civilization in Niven and Pournelle’s Footfall? Or would they have to look for specifics? Or would it be impossible?

What things we’ve done, right now, would be a sign for them? I argue in the thread that large quarries would last a very long time and be fairly obviously non-natural events. But there must be others.

They’re not millions of years old at this point, but lots of underground sites should be able to last quite well; many have already lasted quite well through a few hundreds or thousands of years without maintenance. Many medieval sites got destroyed more by their use as “second-hand quarries” than by neglect.

While cave paintings, or caves which once held long-gone-to-dust casks of wine in their beds of carved stone, are not evidence of an* industrial* civilization, I’d be quite impressed if we found a place where dinosaur pawprints were surrounded by pigment.

My guess would be that some large underground structures (subways, etc.) would last long enough to at least be detectable, even if they weren’t entirely intact.

There will be some surprises when they dig into our bigger garbage dumps. Plastics will break down given centuries but the process is slower yet when buried deep.

Ceramics in dumps should last a very long time, some will survive a million years. The structure if the dumps themselves might reveal they were made and not natural. Glass bottles can last a million years.

How many ice ages occur will effect the answer. They do end up effectively scrubbing the land to some degree.

10 million years is an interesting time-frame as there’s likely to be another ice age or two which will destroy much of the record of the northern hemisphere and is long enough besides for other erosion processes to act. Open-cast mines and quarries would get softened or filled in.

My first thought is salt mines. Whatever is in one of those will survive indefinitely as long as there’s no water ingress. And the mines themselves will themselves be evidence of industry.

Pottery. Complete objects would be nice, but shards would suffice.

Graves with grave goods - likely rings & jewellery.

What we’ve left on the moon will still be there in 10 million years’ time. Other space stuff might still be up there too.

Personally I think the most lasting things would be large earthmoving projects where we’ve dynamited cuts through hills and mountains for roads and railroads.

That sort of thing will be around until geological processes remove them, unlike a lot of other man-made stuff.

Granted, it may take quite a while for whatever follow-on civilization to realize “Hey! That valley is entirely unnaturally placed based on what we have discovered about geology!”, but I think it would be pretty obvious.

Engraved gold bars should last indefinitely as long as someone or something can find them them. They are expensive but noncorrosive. You could pass a limited amount of information that way. There are probably some other really stable metals that would last that long as well. Some types of stone can last much longer than a million years and you can engrave them as well especially if they are stored underground.

This story is a fictional account of discovery of traces of an ancient civilization, but I think the items it suggests as potential traces (unusual chemical compounds) are realistic.

Would the satellites still be in orbit? If the raccoons can make it to the moon, the plaque with Nixon’s name on it should still be there.

If it has to be Earth-bound, there is a vault in the Arcticthat holds a lot of different kinds of domesticated seeds that might still be there.


In 1,000,000 years; even if the orbits wouldn’t decay on there own, enough micro-collisions would occur to knock them out of orbit.

In that kind of time frame I doubt that much would be readily identifiable as made rather than naturally occurring “freaks”. Even with some arch discovered buried hundreds of feet underground I can see some Future Me saying “I ain’t buying it. Civilization that long ago? Impossible. That doesn’t come close to being proof.”

The pyramids.

The Panama canal.

The actual objects don’t have to survive over that time frame. Anything buried by sediments could fossilize. Even if plastics degraded, or metal objects corroded, they would leave an empty space that could form a mold or cast fossil. And tracks leave fossils too; bulldozer tracks and the tracks of off road vehicles could leave impressions that would be visible for hundreds of millions of years.

Certainly not over a scale of millions of years. The area of the canal was still probably open water about 3 million years ago. In 10 million years, continued tectonic movements will squeeze Panama up against South America so that it is no longer recognizable. The canal itself will probably sediment in within a matter of centuries.

Absent plate tectonics and glaciation, buried ceramic objects will last for a long, long time.

And many other man made components that do not occur naturally will too. Nuclear wastes, cores of nuclear weapons, man made materials like tungsten carbide, may not be understood for what they were but a smart raccoon should be able to tell that they could not occur from natural processes.

The equipment we have sent to the moon should still be there for millions of years. On Earth fossilized bones last millions of years, glass items should last longer, if they are away from the oceans. Glass does not require the fossilization process that bones do. A cut diamond ring even longer.

We know only a little about the early Homo genus’ from very few fossils, but there were many fewer of them than there are now of Home sapiens. Had there been 8 billion of Homo erectus, everywhere on the planet, millions of years ago, I think we would know quite a bit more about them.

Wind, water, mountains rise, oceans happen where there were none. These are the great erasers. Plate tectonics, subduction, etc. will send everything back into the mantle to be consumed there eventually. The ultimate recycling. But there are still some very old rocks left in various areas of the world. And the footprint of man, the artificial footprint, should last for many millions of years.

I am betting on smart racoons to figure it out. They are already on their way. But the evidence they will find, when all else is erased, will be in the chemical properties of things that must have had intelligent help to happen.

Raccoons will have to invent their own personal Jesus, their own religion, to explain these discrepancies. God help the universe then.

The Pioneer and Voyager space probes are now entering deep space where in theory they could drift for billions of years to the end of the universe provided they don’t collide with anything.

Sure, but there will be these weird discontinuities hidden in the sediment. Not just where the original dirt was dug out 100 years ago, but in all the steel-reinforced concrete that will still be there. Any geological survey will discover all these weird artifacts there.

Hoover Dam fits the bill too. Even allowing for crazy sedimentation and plate tectonics in the coming eons, you’ll have this giant mass of concrete and other materials arranged in unnatural shapes that is geologically inconsistent with the surrounding rock strata.

I read the the thread in GQ as well, but didn’t want to post because I only have an opinion, so thank you Jonathan Chance for this one!
I think if humans still employ modern archeological practices in the far future, there would be a good chance that things would be noticed and studied. In the not too distant past, archeology wasn’t a big thing.
Across the river from St Louis, MO there is an ancient Native American settlement called Cahokia Mounds. This civilization built huge mounds out of dirt that dotted the area. Through historical writings, the researchers believe that there were several in what is now St Louis, but were thought only as hills, so they were razed and leveled to make room for farms, homes etc.
So, today, we notice these things, study them, build around them etc. In a million + years it’s hard to say if people will still care enough about the past to continue to do things like that.

The concrete will break down in 10,000 years tops and might not leave any obvious tell-tales. It will probably largely break down within a few hundred years of no longer being maintained.

dorvann: correct about the space probes, but no reasonable chance of being found by our terrestrial successors.