Some disaster, disease, an asteroid, more likely a nuclear exchange and subsequent nuclear winter, wipes out most of humanity. The few humans remaining are obviously reduced to a stone age type existence. How long before traces of our civilization disappear? Cement, asphalt, other artifacts, etc. reduced to dust which, only when civilization and science re-emerge after thousand and thousands of years, are investigated with all kinds of wild theories about past civilizations then being propagated.
What I mean is, how possible a scenario like this for the history of Earth? It’s been over 4 billion years that this planet has existed. That’s a long time. Civilization after civilization… Human beings always getting to the same place … Nuclear war after nuclear war…
Not very possible.
Humans haven’t existed for billions of years, so that reduces your timescale considerably. Further, we can find fossils from pre-human homonids and can find traces of early stone age hunting camps. We have dug up the earth quite a bit but never have we found any traces of realy advanced stuff.
You would think that remains of an asphalt road or concrete foundation would be a lot easier to find.
For chemical erosion on the surface of the earth, a few days in the case of rock salt, 100x thousand years to x million years in the case of calcite. Your building concrete, human and animal bones will last about as long as calcite. For silicates, that includes your quarried granite structures and all kinds of ceramics, anything from 10x million to 1000x million years. Climate and climate change, not to mention whether or not you are above sea level, has a lot to do with rate of weathering.
Your best bet at preservation is for your relics to be buried and lithified. That’s how fossils are formed. If your want even buried fossils to disappear, they must either be exposed at the surface and be weathered/eroded, or, they can be deformed, altered and metamorphosed sufficiently to erase traces of the fossils and relics. That could also take a billion years to happen.
There’s an interesting documentary on this topic “Life after people”, that adress part of this question. It explains how long it would take for instance for buildings and monuments to collapse and how it would happen, for roads to dissapear, etc… Though IIRC it doesn’t go as far as stating how long it would take for every trace of civilization to dissapear.
It seems to me that in a previous thread about this topic, it was mentioned that the past existence of our civilization could be detected for a very long time due to the abnormal concentrations of chemicals, metals, etc… in some areas.
Still, is it possible to rule out the possibility that there has been, say, a dinosaurian civilization 150 millions years ago?
I once listened to a pre-cambrian geologist, and he made a case for chemical imprints for processes and various features that are now lost to us. He’s trying to apply it economic geology. For instance, he believes there are more porphyry copper and gold deposits being formed today than in any other period in the Earth’s history. A geologist with a different field of specialization, say plate tectonics, might conclude the same thing.
I can think of a number of definitions of “civilization” wherein the only token of it 150 million years later would be fossils of the citizens. No traces of industrialization, ordered settlements, and use of various durables.
Could there have been a Tithonian dinosaur civilization that has left no trace whatsoever? Yes, it’s “possible”, in the same way it’s “possible” there’s a hidden valley in the Alps populated entirely by unicorns and dryads.
Is it possible to rule it out, though? Of course, even easier. Firstly just by applying Occam’s Razor. There’s zero evidence for such a thing, why even suggest it as a possibility without any need?
I did a quick search for “oldest fossil” and results for 3.5 billion year old bacteria fossils appeared. So there doesn’t seem to be an expiration date on fossils. Which means that anything stronger than a fossil or anything that will fossilize can pretty much stay around forever, given the right conditions. Obviously it wouldn’t be laying around for a casual observer to spot after a few million or billion years, though.
This was done in a pretty good thread within the last few months.
One non-expert person suggested evidence would be conclusively erased by crust plate subduction. Once your cities or garbage dumps or mines have been sucked into the mantle, those atoms will eventually re-emerge onto the surface utterly scrubbed into normalcy.
One of the geologists pointed out that he was right that subduction would be a comprehensive eraser. But … we still have a lot of original crust on the surface. Yes, there is subduction constantly consuming crust and seafloor spreading constantly creating new crust. But nothing requires that it all get recycled periodically. The interiors of continents are very, very stable over multiple billions of years.
Speaking just for non-expert me …
I could imagine things like clothes and using fire and making simple stone tools could have developed more than once in human history. Maaaaybe some group got as far as primitive animal husbandry or sharp-stick level agriculture. And that some of those “advanced” small populations lived and died on land that’s now underwater and as-yet unexplored. And that they predated the population that survived to become us.
But nothing bigger or more advanced than that makes much sense. There almost certainly hasn’t been time for any other unrelated intelligent species to develop, flourish, and die off.
Well, we can put an upper limit on it at ~5 billion years. At that point the earth will be enveloped by the expanding sun’s outer layers, causing it to spiral in and vaporize. Should pretty much take care of anything left behind…
Subduction generally recycles oceanic crust (greenstones/ophiolites notwithstanding) because continental crust generally “floats” on top of the subduction zone, as its density is much less. Oceanic crust is also less dense than mantle rock, but denser than continental crust, so is preferentially subducted. If two continental crustal blocks collide, you ca**n have deep melting of continental crust, like below the Himalayas or the Alps. But that occurs at the bottom of the continental crust and leads to granitic-type melts, not in the mantle itself. Generally, over Earth history, the continents have been growing larger. Rapidly at first (around the Paleoarchean period) and later slowly but steadily.
The fact that we found huge ore deposits suggests that no previous technological civilizations could have existed. Turned around, this means that if through some disaster we reverted to the stone age, then civizilation could not be reinvented, at least not in the present form, because we have removed the low-hanging fruit of resource exploitation and could not get it going again.
There was another thread like this recently. Artifacts will get buried in mud and dirt and last millions, maybe billions of years. Huge artifacts like the Great Pyramid may still be standing millions of years in the future, though possibly buried also. In the right conditions lots of metal and plastic, and even paper and wood will be preserved for eons. Simply eliminating humans won’t do much to destroy the things we’ve created.
The trick for our primitive descendants will be to mine our garbage dumps, not Earth’s depleted native ore beds.
Given that half of current humanity lives near the (rising) seashore that may prove hard for our descendants to do. They’ll be needing to invent SCUBA or submarines first to even find most of our dumps. Sucks to be them.
And a sampling of other threads that touch on the subject – for example, asking if ancient human or alien civilizations could have been here and then disappeared, with all traces of their presence having been lost:
Once again, I recommend The Earth After Us, a great little book by Jan Z. (Polish last name I can never spell from memory, but you’ll find it easily).
The upshot is, most land-based evidence will disappear due to erosion, and most sea-based evidence will disappear due to the aforementioned subduction. There will be fossil evidence of climate change and anthropogenic extinctions and movements of species, but it will be difficult to ascribe this to one particular species of upright ape. The best hope for direct evidence (fossilized computers or hubcaps or sidewalks, etc.) will be from the chance preservation of a built environment in a place like New Orleans: near the mouth of a big river, so a block of sediment can submerge and lithify in a shallow sea far from an active plate margin.
Some of the materials we have made should last much longer than the 5 billion year limit that StrangerThanFiction points out. I think blocks of very inert metals (such as the standard kilogram) would, for instance. It may not be very easy to notice, but “all traces” are practically impossible to erase in the context of Earth’s future. There are plenty of examples of dumb old rocks that have lasted nearly since Earth’s formation, through much more active phases of geology than we are going to see until the Sun consumes us.
Someone already mentioned Voyager. Also, even if everything on Earth is buried or destroyed, there should still be some items recognizable as a product of a non-natural process that we left on the moon, and anyone stumbling across them should probably be able to figure out that they came from the planet below rather than the gray, sterile moon.
