4 ms·

I saw a study recently, unfortunately I can't locate it now. It discussed the possibility of there having been past civilizations on Earth, hundreds of million

I saw a study recently, unfortunately I can't locate it now. It discussed the possibility of there having been past civilizations on Earth, hundreds of millions or even billions of years ago. The conclusion was that this can't be entirely ruled out. It noted how few actual fossil remains we have for what we know of dinosaurs, and that there's a lot of space left in those gaps for all the evidence to have been destroyed.

caymanjim 7y ago
It's incredibly improbable. While much of the planet's surface is recycled constantly, there are also huge swaths of land that are billions of years old and haven't changed enough to hide evidence of complex society. Dinosaur fossils are rare, but not that rare. Tiny ones are abundant. If all life on earth ceased today, you could come back here in a billion years and find plenty of evidence everywhere. Maybe it's not 100% impossible, but it's so improbable that it belongs alongside other fringe theories.
- TheOtherHobbes 7y ago
  I like to entertain a mad fringe theory that the K-Pg asteroid was a war weapon. You might think no species would be insane enough to consider bombing its own planet to the point of extinction-level oblivion, but - that doesn't appear to be true.
- yellowapple 7y ago
  > there are also huge swaths of land that are billions of years old and haven't changed enough to hide evidence of complex society Do you have any examples? The article in the sibling comment to yours directly states that the oldest large-scale swath of land (in the Negev Desert) only dates to 1.8 million years.
  - caymanjim 7y ago
    That's the oldest surface land, but the oldest crust is 4.4 billion years in Australia, and there are other places with less-old-but-still-billions crust. Natural erosion in those areas exposes extensive history, and we can dig too. [1]: https://news.nationalgeographic.com/news/2014/02/140224-oldest-crust-australia-zircon-science/ https://news.nationalgeographic.com/news/2014/02/140224-olde...
    - yellowapple 7y ago
      Surface land (current or former) is the only really relevant source of potential evidence here, though (unless we're specifically looking for subterranean civilizations, or perhaps for remains of old mines or wells).
      - caymanjim 7y ago
        Surface land is a bit of a misnomer here. While the crust is 4.4B years old in Australia, that doesn't mean all 4.4B years are sub-surface. The top surface there is new, but there are exposed areas going back billions of years. This is how all fossils are found; the oldest surface is the 1.8M Negev desert, but we constantly find 300M year old dinosaurs sticking out of the sides of river valleys and other eroded areas. My point is that we'd also find evidence of a billion-year-old advanced civilization the same way, and that in Australia in particular, you can go all the way back to the formation of the planet.
hesk 7y ago
Maybe it was this? Gavin A. Schmidt, Adam Frank: The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?, https://arxiv.org/abs/1804.03748 https://arxiv.org/abs/1804.03748 I found it through an article in The Atlantic that may or may not have been linked on HN recently. https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e...
- CWuestefeld 7y ago
  Yes, I believe that was it. Thanks!
- lioeters 7y ago
  Indeed, there was a discussion about this article, about a year ago. As a fan (and amateur writer) of science fiction, I greatly enjoyed learning about this hypothesis. Was there a civilization on Earth before humans? https://news.ycombinator.com/item?id=16837120 https://news.ycombinator.com/item?id=16837120
yongjik 7y ago
I am not a geologist, but it seems improbable for a technical civilization (like our current one) to not leave a global geological mark. For example, our use of fossil fuels changed global carbon isotope composition: our atmosphere now has less portion of C13, because photosynthesis favors the lighter C12 atoms, and all our fossil fuels ultimately derives from photosynthesis.[1] The changed isotope ratio will be detectable in every carbon-containing sediment layer ever produced in our age. And this is just one example. [1] https://skepticalscience.com/print.php?r=109 https://skepticalscience.com/print.php?r=109
- timClicks 7y ago
  How long would a civilisation need to survive in order to leave a geological impression?
- nems808 7y ago
  Look up the PETM (Paleocene Eocene Thermal Maximum), there's definitely a d13C signature there.
Nition 7y ago
It's amazes me a little that we have as much from the dinosaurs as we do, considering how long ago they lived. For many of them it's less than 100x the time between us and them, to go back to the beginning of the entire universe.

caymanjim 7y ago

It's incredibly improbable. While much of the planet's surface is recycled constantly, there are also huge swaths of land that are billions of years old and haven't changed enough to hide evidence of complex society. Dinosaur fossils are rare, but not that rare. Tiny ones are abundant. If all life on earth ceased today, you could come back here in a billion years and find plenty of evidence everywhere. Maybe it's not 100% impossible, but it's so improbable that it belongs alongside other fringe theories.

TheOtherHobbes 7y ago
I like to entertain a mad fringe theory that the K-Pg asteroid was a war weapon. You might think no species would be insane enough to consider bombing its own planet to the point of extinction-level oblivion, but - that doesn't appear to be true.
yellowapple 7y ago
> there are also huge swaths of land that are billions of years old and haven't changed enough to hide evidence of complex society Do you have any examples? The article in the sibling comment to yours directly states that the oldest large-scale swath of land (in the Negev Desert) only dates to 1.8 million years.
- caymanjim 7y ago
  That's the oldest surface land, but the oldest crust is 4.4 billion years in Australia, and there are other places with less-old-but-still-billions crust. Natural erosion in those areas exposes extensive history, and we can dig too. [1]: https://news.nationalgeographic.com/news/2014/02/140224-oldest-crust-australia-zircon-science/ https://news.nationalgeographic.com/news/2014/02/140224-olde...
  - yellowapple 7y ago
    Surface land (current or former) is the only really relevant source of potential evidence here, though (unless we're specifically looking for subterranean civilizations, or perhaps for remains of old mines or wells).
    - caymanjim 7y ago
      Surface land is a bit of a misnomer here. While the crust is 4.4B years old in Australia, that doesn't mean all 4.4B years are sub-surface. The top surface there is new, but there are exposed areas going back billions of years. This is how all fossils are found; the oldest surface is the 1.8M Negev desert, but we constantly find 300M year old dinosaurs sticking out of the sides of river valleys and other eroded areas. My point is that we'd also find evidence of a billion-year-old advanced civilization the same way, and that in Australia in particular, you can go all the way back to the formation of the planet.

hesk 7y ago

Maybe it was this? Gavin A. Schmidt, Adam Frank: The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?, https://arxiv.org/abs/1804.03748 https://arxiv.org/abs/1804.03748 I found it through an article in The Atlantic that may or may not have been linked on HN recently. https://www.theatlantic.com/science/archive/2018/04/are-we-earths-only-civilization/557180/ https://www.theatlantic.com/science/archive/2018/04/are-we-e...

CWuestefeld 7y ago
Yes, I believe that was it. Thanks!
lioeters 7y ago
Indeed, there was a discussion about this article, about a year ago. As a fan (and amateur writer) of science fiction, I greatly enjoyed learning about this hypothesis. Was there a civilization on Earth before humans? https://news.ycombinator.com/item?id=16837120 https://news.ycombinator.com/item?id=16837120

yongjik 7y ago

I am not a geologist, but it seems improbable for a technical civilization (like our current one) to not leave a global geological mark. For example, our use of fossil fuels changed global carbon isotope composition: our atmosphere now has less portion of C13, because photosynthesis favors the lighter C12 atoms, and all our fossil fuels ultimately derives from photosynthesis.[1] The changed isotope ratio will be detectable in every carbon-containing sediment layer ever produced in our age. And this is just one example. [1] https://skepticalscience.com/print.php?r=109 https://skepticalscience.com/print.php?r=109

timClicks 7y ago
How long would a civilisation need to survive in order to leave a geological impression?
nems808 7y ago
Look up the PETM (Paleocene Eocene Thermal Maximum), there's definitely a d13C signature there.

Nition 7y ago

It's amazes me a little that we have as much from the dinosaurs as we do, considering how long ago they lived. For many of them it's less than 100x the time between us and them, to go back to the beginning of the entire universe.