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So Humans went extinct in the future, they are completely gone, but their buildings are not. Now it's 10 million years in the future, and I want to know what could plausibly still be visible on the surface.

In the centuries preceding their disappearance, they had switched from concrete 'n steel to a material called handwavium. Handwavium is very resistant to erosion, no biological process breaks it down, it is much stronger than steel, and like gold, it is very hardy against the elements, and it doesn't corrode. It will not be wethered away in 10 million years. Most of any buildings is made from it, as it is deployed by 3D printing. Maybe with a superstrong metal beam inside it for support. Handwavium is used in everything in the future because through the (Handwave) process it can be easily recycled. Although skyscrapers would still collapse in 10 million years from just the stress of holding their own weight, and large/maybe medium buildings as well.

On top of that, they also build their buildings to be very stable and resistant to collapse from weathering, the elements, etc. Although weak points in the building and the stress of its own weight will still cause its demise eventually.

Now, let's take the city of New Atlanta(The city of Atlanta, Georgia), a very dense city with everything from skyscrapers to suburban neighborhoods. After 10 million years, how much of the city could still plausibly be visible on the surface? Could there be debris and household items littering the surface?

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  • $\begingroup$ Where is the city of New Atlanta geographically? The city's altitude and proximity to coastlines, fault lines and other factors will determine if the city is likely to have been buried or parts are still visible, especially with ice age/s. Also, if handwavium will not decay, corrode or appreciably erode then why would the skyscrapers collapse - are you thinking that the foundations will eventually be undermined? $\endgroup$ Apr 14, 2023 at 14:41
  • $\begingroup$ New Atlanta Was just how I referred to Atlanta because of "Future."As for why I believe skyscrapers would collapse, is that there would still be weak points in a skyscraper, plus the stress of holding that much weight for so long would eventually get to even that. $\endgroup$
    – KaffeeByte
    Apr 14, 2023 at 14:44
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    $\begingroup$ Buildings only really fall under their own weight whenever the people building it do an awful job at it, which you'll find isn't the case for multimillion-dollar buildings. Buildings are built to easily withstand their weight (especially if made of this handwavium stuff). If you really wanted the buildings to collapse, then natural disasters are the way to go, as even a flood can loosen the foundation upon which the building stands, leading to it sinking in the ground, and eventually collapsing from uneven ground. $\endgroup$ Apr 14, 2023 at 15:26
  • $\begingroup$ Not enough for an answer, but let's not overlook the "mega engineering" projects that literally reshape the landscape. Some are obvious like Mt Rushmore, but even something like massive earthworks that underlie the rail and freeway networks. Long after the rails and concrete have rusted, the cuttings, massive earthen embankments and the like will be buried under vegetation just waiting for some extraterrestrial to come along and use their equivalent of ground penetrating radar and infrared visualisation technologies. $\endgroup$
    – elemtilas
    Apr 14, 2023 at 23:21
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    $\begingroup$ Does this answer your question? Erosion of buildings on geological timescales. This question has been asked many times and in many forms on this Stack. If you believe yours isn't a duplicate of the many others, please indicate specifically why none of those other quesitons answer yours. $\endgroup$
    – JBH
    Apr 15, 2023 at 3:40

3 Answers 3

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Slim to None

Handwavium skyscrapers: Atlanta gets frequent severe lightning storms, regular hurricanes, seasonal floods, regular freezes, and occasional earthquakes (1-in-1000 annual probability of a 7.0 temblor).

After a few millenia ...or tens of millenia... of monumental superstorms, major earthquakes, and freeze-thaw cycles without any repair or maintenance, the skyscrapers will be on the ground.

Erosion: After millions of years, ordinary erosion will have reshaped the land. Ordinary (non-skyscraper) buildings will be washed away or smashed by ordinary hurricanes and flooding and tornadoes. New streams will appear when sewers clog and overflow. Foundations and parking lots will subsequently be carved away by the new running streams or buried under meters of sediment.

The handwavium skeletons of the fallen skyscrapers will also be eroded by streams, or in places will accumulate sediment to create strange hills.

Vegetation: Vines will climb handwavium stalks. Wind-blown seeds will find high perches. Sediment-covered parking lots will become grasslands, and then woodlands, then forests. Roots will inexorably smash old human-made barriers. All the vegetation...and accompanying wildlife...will obscure any evidence of civilization from casual observation.

Time: Ten million years is a really, really long time. The Great Pyramids have existed for 0.05% of that time. (Not 5%, 0.05%!) The Grand Canyon is barely half that age. Several dozen ice ages have come and gone in ten million years. Yellowstone may erupt...a dozen times. A whole new intelligent species may evolve from something unexpected. It's that long.

So, will there be evidence that a city existed? Sure, lots of it...clearly available to any future archaeologist or paleontologist who grids out a dig zone and starts shoveling. But not obvious for any casual visitor through the Atlanta forest, with it's curious linear hills and mysterious sky-vine trees.

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Life After People is a good documentary that explains what would happen to the remnants of human civilization after people disappear. It uses the expertise of people in the fields of study that would know best on how the environment would bring an end to everything we created.

Although they do not expressly discuss the robust nature of "handwavium" they do discuss some other materials that would become artifacts of our existence. One of the products they discuss is plastics. Even with its in resistance to naturally break down in the environment, it is still theorized that much of it would take around a couple million years to be removed from the environment. Much of that time, most of the plastics would be in the form of micro plastics as big pieces would be battered and smashed by natural events into smaller bits. Landfills and areas of accumulation of plastics would protect some of it to become nothing much more than a techno signal to future beings to find, much like a mineral traces in the geological strata for our time period in history.

Another point that would ensure this "handwavium" would break down is that, if it can be recycled, you better bet the environment will break it down eventually. It may take 1 or 2 million years, but it will fade over time.

Weirdly enough though, the program I mentioned did state that the pyramids in Egypt will last for many millions of years. It may be the longest lasting proof humans existed other than the micro-plastic traces in the fossil record. If your cities are built in such a way that large masses of material are stacked into a small area, it would definitely catch some future archeologist attention.

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  • $\begingroup$ I'm aware of "Life After People," it was my favorite thing to watch :D, but they don't really go into much detail or even explore time periods past thousands of years often. I think they only ever mention time scales of around 10 million years maybe 5 times at the very most, and not much detail is really given. As for recycling, it wouldn't matter, nature cannot break down the material yet, regardless of recycling or not, according to the rules of handwavium. $\endgroup$
    – KaffeeByte
    Apr 14, 2023 at 17:51
  • $\begingroup$ Not sure about the pyramids lasting millions of years though, they had a fair amount of erosion in less than 5000 years, not to mention that in millions of years, the climate would change many times, heck I think I read once that the Sahara would be green in less than 100,000 years. $\endgroup$
    – KaffeeByte
    Apr 14, 2023 at 17:54
  • $\begingroup$ There is a reason they dont explored time frames greater than 1000 years. Not much of anything we have made, even the most robust of materials, will survive over those time scales $\endgroup$
    – Sonvar
    Apr 14, 2023 at 18:06
  • $\begingroup$ Yeah the only reason the humans have handwavium is that they are K2 civilization(or technically K1.9 or something around that) $\endgroup$
    – KaffeeByte
    Apr 14, 2023 at 18:12
  • $\begingroup$ @KaffeeByte not sure of the validity of the claim the pyramids would last millions of years, its just a statment the program said, due to its size and high concentration of rock unnaturally located in one location. It may not look like a pyramid in 10 million years, but you would be able to tell something massive was there. Now a K2 civilization (on the kardashev scale) would leave much more evidence of there existance. Im thinking the city ruins on the moon, massive derilict stations on sol orbit and the remenants of a dyson swarm would indicate human presence $\endgroup$
    – Sonvar
    Apr 14, 2023 at 18:18
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Nothing is left on the surface.

there will be artifacts, like glassware or strange rocks but no structure is surviving that long. And that is just survive they won't be on the surface they will be buried, if they were not buried they will have been destroyed. It doesn't matter how much you handwave it thermal cycle stresses and abrasion can destroy anything made of matter in 10 million years. once a single piece of handwavium is broken loose then erosion is beating handwavium against handwavium. Frost wedging can powderize mountains and chemical reactions can dissolve hundreds of meters of solid rock in that amount of time, even gold corrodes and dissolves on that timescale. glaciers can expand and retreat dozens of times, and nothing is glacier resistant.

Also as a side not if it is easily recyclable then handwavium can't be erosion resistant, easily recyclable materials have to be easy to breakdown and separate from other materials.

It doesn't matter if your material is harder than diamond, stronger than steel, and as chemically inert as gold all at the same time, it is still long gone if it is on the surface.

If the areas is depositional vegetation will bury everything wiping it off the map, if it is erosional then everything is long destroyed. Even the rock the buildings were built on top of is long gone, even magic skyscrapers can only last as long as the ground they are built on is still there.

Archeologist might be able to find them by digging but nothing will survive the surface of the earth for that long. You might find small artifacts that were buried and eroded out but they will be few and far between.

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