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The longevity of man-made objects and structures

  1. Jun 16, 2015 #1
    I'm beginning a science fiction novel that begins a billion, or possibly several billions, of years in the future. Given the best quality structures humans can make out of the longest lasting materials we have, what would buildings and other structures look like after that long of a period of time? And that is exposed to wind, rain, snow, and even the intense heat of the sun far into the future.

    What about underground structures that aren't exposed to the elements? Do they still show signs of degradation after billions of years? Would they even exist as structures after that long? Even if they're metal or glass?

    What about an object made of various materials kept in a vacuum? Would it still show signs of degradation after such a long time as billions of years?

    I know what happens to things in certain conditions after hundreds or even thousands of years, but after billions, that's a whole other story.
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  3. Jun 17, 2015 #2

    Simon Bridge

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    On the timescale of billions of years, continental drift is also a factor. So is climate change. Possibly planetary reformation (1billion years is the same order of magnitude as the age of the Earth). (taking "1 billion" to mean 1 thousand-million or 109 ).

    Assuming nothing really cataclysmic, like the event that formed the Moon... and if we just count the bilion years from today so we don't have to worry much about the Sun going unstable... (the time-frame is 10% of the expected solar lifetime, which we are about half-way through.)

    Any structure on the surface would be buried, maybe subject to severe ice ages. Some parts of the world they would suffer subduction.
    The weight of billion-year strata squashes most things very flat ... life (i.e. cyanobacteria) is detectable in rocks in that sort of time frame.
    Does that count as a "structure"?

    So: pretty much everything we build in the modern world would end up as a weird smear in the strata - to puzzle future geologists.
    Vacuum containment - for example - has to be maintained. All seals leak, all container materials wear out or get squashed, in well under the time under consideration.
    Once the container has decayed, the materials inside would be exposed. Even if it were perfect, it would also have to be impervious to radiation. Whatever is contained may (almost certainly) contain radioisotopes too - so the substance changes over time even isolated. High technology, though powerful, is fragile.

    How to go about building a monument that would say "we were here" in a billion years time is an intriguing engineering question that requires some subtlety to approach it. The related, and more fundamental question, "if there were an advanced civilization around a billion years ago, would we notice" is also fun.

    If we were to deliberately build something to last billions of years, then we'd want to make it out of some super-hard crystal or just make it very big (a 1018kg ball of rock should do the trick) especially if we also put it in orbit. We'd have to be very careful about the orbit - orbital decay is going to be very significant (collisions with other objects, drag from solar wind, dust, etc). The lack of large oil deposits in shale may be a hint to future geologists but maybe they won't expect them or maybe new oil deposits would form in the meantime. A strange lack of fissionables could cause some puzzlement among physicists.

    But basically - everything dies.
  4. Jun 17, 2015 #3
    Look at any exposure of early Paleozoic rocks. They have not lasted a billion years, but they have lasted half of it. Trilobite shells were not made of indestructible materials - trilobites could not grow any, and plenty of predators and scavengers were adapted to presence of shells. Yet macrofossils are both common and obvious.

    A lot of manmade devices have good fossilization potential. And the bones of men themselves - in some soils they dissolve in a few decades, in others they last tens of thousands of years, and would last hundreds of millions of years, like those of dinosaurs have.
  5. Jun 17, 2015 #4
    As inspiration you may watch "Life After People" on youtube, but they show usually shorter time frame.

    Ocean - nothing - by this time all oceanic floor would be recycled
    However underground structures and stuff that would be quickly covered with seidements would be quite fine. Plenty of plastic and glass should survive. Just finding human skeleton would be more tricky ;) Also nuclear waste would survive, just would not be a specially strong radiation source.

    Satellites on geostationary orbits?
  6. Jun 17, 2015 #5
    Thanks for the responses.
    So if they're underground, they're going to need to do some digging to get back to the surface. And that's if the structure they were in is capable of remaining a structure under all that weight. Putting them in orbit around the Earth or maybe having them on the moon would work. I could make everything out of diamond, which wouldn't degrade... probably. It doesn't react with anything, does it? It apparently can be ignited at about 700 degrees C. That's pretty low for the conditions it's going to be in (>2500 degree C temperatures). Any other materials that are extremely strong, have a high melting point, and a resistant to degradation? That's a tall order, I know.
    How long does even the most durable and long-lasting plastics last? When you're talking about a billion years, you basically need something that lasts forever.
    Thanks again.
  7. Jun 17, 2015 #6
    As a geologist I'd be confident in saying nothing or next to it would survive a billion years. Or...the odds of finding something buried under a kilometer of formation layers would be zip.

    Don't think of things like sun, water, decay, etc. Those are temporary blips over a few tens of thousands of years. Think of forces like plate tectonics...continents moving, the burial of today's surface under a kilometer of rock...ground up, exposed, buried again.

    Then the odds of finding that one in a 5 billion item that wasn't obliterated? Macro fossils exist from a half billion years...but they are small lenses from an instant of time...something lucky was happening to preserve a Cambrian trilobite...that moment. If it was a moment any time a million years before or after and no such preservation. Also, that's a half billion years...double that and the odds are that all macro fossils would be obliterated....that's another 500 million years of plate tectonics, etc.

    Perhaps some evidence of humans might survive on the Moon but that's beyond my expertise.
  8. Jun 17, 2015 #7


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    This timeline gives some good references of what has happened in the last 5 billion years.
    Continental drift would be beyond significant.

    Check this https://en.wikipedia.org/wiki/Oldest_dated_rocks

    First you have to find old rocks, and then they have to somehow contain life signs from 5 billion years before.

    I expect many super volcanoes, asteroid /comet collisions, solar bombardment, etc. New species, new intelligent life forms. Possibly sterilization from nearby supernova https://en.wikipedia.org/wiki/Near-Earth_supernova. 5 billion is a lot.
  9. Jun 17, 2015 #8
    How lucky the next race - because if damn lucky some high quality remains would after tectonic movement appear almost at surface.

    If they are unlucky they would rather discover something during digging a mine. No idea how a metamorphic rock made of plastic waste heap look like, but possibly it would not be easily identifiable as artificial. Also human era could leave a mass extinction or a a layer with a bit weird isotope composition after nuclear tests.
  10. Jun 17, 2015 #9
    In your story do you remember to adjust for:
    -continental drift (there can be found online future maps)
    -stronger glowing sun
  11. Jun 17, 2015 #10
    Or erosion.
    Are the houses of Pompeii "structures"? The roofs and any upper floors collapsed under ash - the vertical walls did not, and were encased in ash inside and outside the rooms. So they remained for 2000 years, and would remain for 2 000 000 000 years unless eroded away 10 000 years or 100 000 000 years hence.
    How long does wood last? In Carboniferous coal, it is no longer "wood" - but tree trunks, roots etc. are recognizable in coal.
    Would people mining abandoned coal mines 300 million years since find iron tools and complex machines (the latter crushed by collapse of mine tunnels), and corpses of miners killed in collapses?
  12. Jun 18, 2015 #11

    Simon Bridge

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    You got a reference for that? 2 000 000 000 years is a Long Time.

    Anyway - "unless eroded away..." that's a pretty big "unless".
    What are the odds that the ash would not get eroded away over a billion years ... the ash and pumace burying pompeii was light and uncompressed but over a geologic time frame (1 billion years) you should consider the possibility of being further covered by something heavier ... the site is right next to a volcano after all ... and you should probably factor in at least one ice age (iirc there were 4 in the last billion.)

    It may be that there will be no reason for people to be digging for coal, a billion years in the future, in the sites of modern coal mines... wouldn't they be more likely to dig for coal where new seams have been laid down? Look up how long it takes for coal to form.

    The question of what our finest structures would look like after a billion years has the short answer: "buried, and all but obliterated".
    Nobody is saying that it is impossible for anything man-made to survive so long or that we couldn't engineer something that would - just that there would be very little left.

    I think what is important here is the narrative role played by the remains in the story.
    For a hard SF story involving uncovered remains of billion-year age - expect it to take some effort to figure out what they are the remains of.
    Signs of the billion-year past civilization are likely to be subtle ... unless that civilization has made a deliberate and concerted effort to achieve a lasting monument.
    In most SF, the remains are some advanced material, buried, on another planet - like the "Martian" ruins of Richard Morgan - there is a reason for this.
  13. Jun 19, 2015 #12
    I guess some future explorers of our planet, whether or not they are indigenous species or aliens, or robots, they will discover a thin layer of peculiar items , like bits of silicon seemingly deliberately arranged in intricate forms, which can't be explained by natural processes, but yet don;t seem to have a discernible purpose.
    Most likely conclusion , these were some kind of primitive art or symbolic religious artifacts.
  14. Jun 19, 2015 #13
    Not really. Those types of layers would be ephemeral in geologic time.

    Any aliens with interstellar travel would have vastly superior technology...way beyond what we can conceive, so they might detect some aberrant radiation or quantum phenomenon.
  15. Jun 21, 2015 #14
    Thanks for all the help, guys. So basically any building that houses stuff would have tons and tons of weight on top of it after billions of years. I was hoping to have this book set 7 billion or so years in the future, when the sun is expanding into Earth's orbit. After that amount of time, any building would have tons and tons of sediment on top of it, and unless the structure was purposely build to withstand such weight, it would collapse?
    Let's say that structure was built to not collapse, what about the contents inside? What would they be like after 7 billion years if they were shielded from the elements outside, such as sunlight, wind, rain (there would be moisture in the air inside the building), etc? That would depend on the materials, of course. Some materials dry out and become brittle, some rust. But what if they were machines built from materials that don't dry out and don't rust. Is there something else I would have to worry about that would make those machines utterly useless after 7 billion years? That's such a long time that I can't imagine 7 billion years having no effect on anything, regardless of how durable or long-lasting it is hypothetically. Let's say you had a near perfect cube made of the most durable and long lasting material you can think of, after 7 billion years, would quantum mechanical phenomena that makes tiny undetectable changes in a material start to become noticeable after really long time periods? For example, would that cube be misshapen and not near perfect as it was 7 billion years prior? Or do we even need to talk about quantum mechanical phenomena, since maybe gravity itself would flatten or severely warp the machines after such a long time? Just some thoughts.
    Thanks again.
  16. Jun 21, 2015 #15
    A perfect sphere of some very resiliant material would work better than a cube.
    I don't know what the most resilant material possible is, but nothing could be infinitely resiliant.
    Over a very long time the accumulated effects of various tiny distortions caused by different forces WILL lead the perfect sphere becoming imperfect, and after that point the structure is bound to collapse within a relatively short time, (lets say a few million years at best)

    EDiT - afterthought.
    Probably the most most indestructable material possible would the stuff hypothesised to exist in a neutron star - 'neutronium'.
    The problem with that though, is that when you have somehow managed to mine a neutron star to get the neutronium, that stuff no longer being contained by massive gravity could spontaneously degenerate resulting in a gigantic rapidly expanding ball of hydrogen and ...

    (Well it is the sci fi forum.)
    Last edited: Jun 21, 2015
  17. Jun 21, 2015 #16

    Vanadium 50

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    Seven billion years from now your structure might be at the bottom of the ocean - well, if there still were oceans. By that time, the sun will be hot enough to vaporize the oceans and turn the earth into Venus' twin. But in any event, over 7 billion years the movement of tectonic plates probably means that wherever you put this object, it's moved from land to ocean and back, possibly more than once.
  18. Jun 25, 2015 #17
    Not on oceanic plate:

  19. Jul 3, 2015 #18


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    7 billion years is a very tall order. We were having a hard enough time finding some way to get something to last 1 billion years, much less 7 :) After 7 billion years the sun would be in its death throws and Earth would have been a long dead tomb. The oceans would be gone, tectonic activity on the planet would have long since ceased but not before having drastically changed the face of the planet. The Earth probably wouldn't even be in its current orbit. As the sun expands it would also be loosing mass so there is a distinct probability that the planets would loose their current orbits and drift, possibly even leaving the system. Basically after 7 billion years the solar system would be unspooling and any evidence that we were here would be very hard to find. Barring any asteroid collisions, the remnants of the Apollo mission would still be on the moon and the Rovers would still be on Mars.

    If you want the characters of your book to be a second civilisation that evolved here on Earth, I would go with your original time frame of 1 billion years. Keep in mind that even within 1 billion years, not only would the surface have changed but the temperature and atmosphere of the planet would be very different, very likely not hospitable to current humans.

    As others have pointed out, over a billion years most structures would be gone but for a civilization with our current level of technology there would be lots of clues that someone came before them, from weird deposits in the Earth to chemical fingerprints and remnants of artificial elements left behind. For example Plutonium is not a natural element, we made that and I don't know if it would have decayed over a billion years but if did survive, it would be clear evidence for future scientists that someone was there first. Depending how you want your story to go, Archaeologists might discover these fingerprints and argue the existence of a prior civilization, only to be rejected until they put boots on the Moon and discover the flag or find the husks of dead satellites as they begin to explore their skies.

    Its a very exciting prospect and I would be rather interested to hear how your story goes so keep us updated please :)

    EDIT: scratch the plutonuim idea, looked it up and turns out it would have decayed long before your current time frame. but there would still be plenty of other clues for your characters to spot.
    Last edited: Jul 3, 2015
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