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Old 2020-06-09, 14:59   #23
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Originally Posted by rogue View Post
What about the moon and the items left behind by our trips to it? Quick searches in google didn't reveal how much the moon has changed (or not changed) in the past 1e8 years.
Most of the stuff we have left behind is quite fragile but at least weathering rates are low.

My guess is that they should be recognizable artificial for > 1M years. Not sure about 100M

Been few very large-scale (> 10km craters) changes as far as we know, but a hell of a lot of very small scale (< 10m) events.
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Old 2020-06-09, 15:02   #24
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I agree that after a few million years there will be very few obvious signs of todays civilisation on the surface of the earth. But stuff that got buried in sediment will survive in large enough quantities that any geological survey of the earth would find some.

And signs of tunnels etc from mining in stable parts of the earth would be rather obvious to anyone trying to mine the same resources.

Chris
Good point, but perhaps they would start by re-mining the resources we have already dug up? Much the same way that Roman spoil heaps are now regarded as high-grade ore, though those deposits were laid down much more recently.
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Old 2020-06-09, 21:57   #25
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The TV documentary "The World Without Us" based on the book of the same name showed how our impact on the planet would slowly but surely be erased until there would be little left. It mentioned that the monument to the Confederacy on Stone Mountain would be the last visible vestige of our existence.
Disgustingly ironic in view of current events.
https://en.wikipedia.org/wiki/Stone_Mountain
Also, it was mention that the Hoover dam might be another candidate. This dam has so much concrete in it that it is still curing.
The dam would probably be breached but the surrounding structures might still be visible.

The documentary did NOT mention nuclear material in power plants.
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Old 2020-06-09, 23:12   #26
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@tServo: Was thinking along similar "monumental geoengineering feats" lines last night, Hoover Dam and Mt. Rushmore immediately sprang to mind, as did a stray thought about large sculptures and buildings constructed from noncorrosive metals (stainless steel, Titanium as for e.g. Frank-Gehry-designed buildings) in long-term-quasi-stable geologic locales ... then "giant holes in the ground" occurred to me. Considering just the largest open-pit mines in the US, we see that quite a few are located in the desert southwest, i.e. would be subject to similar weathering conditions as Arizona's Meteor Crater, a "mere" 50,000 years old, about which we read:

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Since the crater's formation, the rim is thought to have lost 50–65 ft (15–20 m) of height at the rim crest as a result of natural erosion. Similarly, the basin of the crater is thought to have approximately 100 ft (30 m) of additional post-impact sedimentation from lake sediments and of alluvium. These erosion processes are the reason that very few remaining craters are visible on Earth, since many have been erased by these geological processes. The relatively young age of Meteor Crater, paired with the dry Arizona climate, have allowed this crater to remain almost unchanged since its formation. The lack of erosion that preserved the crater's shape helped lead to this crater being the first crater recognized as an impact crater from a natural celestial body.
Note [a] the crater is in soft alluvial sediments with bedrock only near the bottom, and [b] the rim of the crater is the most erosible portion, thus we can expect the bulk of the crater below the local elevation to survive in reasonably recognizable form for O(million) years. The deeper and less-erosible open-pit hard-rock mines would last much longer ... even those which are filled/filling with water will remain recognizable; the water might even help preserve the site.

As with the fossil record, we shouldn't expect much to survive for multimillions of years ... the question is, will *any* unmistakable traces of our civilization remain, and between massive earthmoving projects, radioisotopic signatures and forever chemicals, I'd say the answer is a clear "yes". Not to mention the classic "bones" part of the archeological "stones and bones" saying - compare the number of people alive now to the estimated number of hominids around at the dawn of upright walking, where remains are scarce and precious, but still get found on a regular basis. The sheer number and geographic spread of modern humans ensures that skulls-a-plenty will exist millions of years in the future. To me the more interesting question is, assuming we go extinct, what would future earth inhabitants of similar intelligence and technical prowess arising millions of years later be able to discern about us from what remains?
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Old 2020-06-10, 07:40   #27
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To me the more interesting question is, assuming we go extinct, what would future earth inhabitants of similar intelligence and technical prowess arising millions of years later be able to discern about us from what remains?
And are we missing the signs of a civilization before ours?
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Old 2020-06-10, 09:06   #28
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And are we missing the signs of a civilization before ours?
As I noted, the only thing we can be reasonably sure about is that if they existed, they did not use much coal as an energy source.

For those unaware of the reasoning: coal is principally fossilized lignin. Plants evolved the use of lignin for structural support long before anything else evolved enzymes to use it as food.

Very little coal has been formed in the last 300M years.
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Old 2020-06-10, 21:53   #29
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Quote:
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And are we missing the signs of a civilization before ours?
If it was populated by creatures with bony skeletons which built habitable structures and/or stone monuments, no. Because we already find evidence of those things for lots of protohumans who lived in small scattered tribal bands, whose key technologies consisted of fire and stone-and-wood-based tools, going back millions of years. "Civilization" implies much larger aggregates of intelligent creatures with significant social organization, and thus, ability to shape and exploit their environment and engage in far-flung economic-trade relationships in ways which leave unmistakeable long-term traces.
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Old 2020-06-11, 00:07   #30
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I may be remembering wrong, but on the time scale of 108 years, according to some theories of how stars work, the earth could become too hot to be habitable anyway.

Some decades ago, I read A Canticle for Leibowitz by Walter M. Miller Jr. If memory serves, it incorporated the idea of human civilization being repeatedly obliterated.
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Old 2020-06-11, 04:39   #31
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Am I the only one that finds this thread to be utterly depressing? No matter what accomplishments mankind achieves they will be obliterated in relatively short order.
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Old 2020-06-11, 04:46   #32
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No matter what accomplishments mankind achieves they will be obliterated in relatively short order.
That isn't necessarily so. We might live on other planets in the future and continue to evolve/innovate/accomplish many great things that build upon current accomplishments.
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Old 2020-06-11, 05:37   #33
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What about the construction of a device that is designed and placed to survive the changes of climate, erosion, plate tectonics, etc? Having it 'float' over various surfaces and using protective strategies and picking a location to start from could extend its utility while unattended.
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