[safety1st]

I think the argument goes that if the civilization was sufficiently old and short-lived, no we probably wouldn't find any fossilized evidence. For example we've only found about one dinosaur fossil per 10,000 years of dinosaur history. The dinosaurs were around for a long time, from 65-250 million years ago. Humans have only been industrialized for around 200 years. If you imagine a dinosaur civilization that's industralized for 1,000 years before it kills itself off, they still hung on 5 times longer than we have so far and yet we probably wouldn't have found fossils of their wrenches. (Not to mention that our archaeology is concentrated on places where humans lived which have little correlation to whatever might have been a good site for a dino city 100 million years ago.)

The authors of the Silurian hypothesis paper believe it's unlikely that there was an ancient non-human industrialized civilization. But they think if there was we wouldn't find its fossils. We might need to look for other markers like climate variances, radioactive materials or artifacts on the moon. Maybe some civilization arose, got stuck in the bronze age or early industrial tech for a thousand years, didn't generate those signatures, then died out. If our fossil record isn't thorough enough to find them then that possibility seems hard to disprove.

Wikipedia has a bit more detail on the Silurian hypothesis: https://en.wikipedia.org/wiki/Silurian_hypothesis

And the actual paper is here: https://www.cambridge.org/core/journals/international-journa...

[ethbr0]

In order for a civilization to be undetectable, you'd essentially bound terms in a terrestrial version of the Drake Equation [0]

You'd need a civilization that did not produce long-lived technological signatures (e.g. glass panes), that did not have a large number of individuals (i.e. produce remains), that did not substantially alter their environment (i.e. leave geographic markers), AND that did not consume easily available resources (e.g. oil/gas or metal ore).

Which is to say... possible, but not very likely.

[0] https://en.m.wikipedia.org/wiki/Drake_equation#Equation

[safety1st]

After 100 million years, would any of those signatures be detectable? Glass decomposes, only takes a million years or so. The continents themselves have rearranged so any bets about structures that still remain are off. Depletion of easily available resources perhaps, but if a bunch of iron deposits were mined out that long ago, how would we know now?

This is the topic of the paper, I think the authors settled on climate markers and radiation from elements like plutonium-239 as among the very few pieces of evidence that might still be around on that time scale. They also observe that there has likely been enough exploitable energy in the form of oil, natural gas etc. to support an industrial civilization since about 250 million years ago.

[ethbr0]

Some glass decomposes.

It's chemically inert like aluminum (after oxidizing, e.g. foil), so the processes acting on it are mechanical and subject to probability.

Some amount is going to be abraded, buried, etc, but you only need a few pieces to remain. Given their ubiquity in our culture, there'd be some somewhere.

[carlmr]

>Given their ubiquity in our culture, there'd be some somewhere.

Yet we can barely imagine a society without wheels, but some human cultures in South America didn't get that idea.

Assuming that every civilization invented glass is very tenuous.

[mbostleman]

To me the most important component is not having a large number of individuals. Which is to say there was not a large amount of physical artifacts of the tech left behind. That seems to me like there would not be enough demand to scale much tech. So it's kind of a circular problem.

[cubefox]

> For example we've only found about one dinosaur fossil per 10,000 years of dinosaur history. The dinosaurs were around for a long time, from 65-250 million years ago.

Dinosaurs presumably fossilize very badly compared to many artificial artifacts, like buildings made out of machined stone.

[withinboredom]

Man, I’ve been in castles that are less than a thousand years old that are barely recognizable. Machu pichu is a good one as well.

[inglor_cz]

Castles that stay above ground, yes, but there likely would be some buried structures, too.

Pompeii looked remarkably fresh when dug out.

[withinboredom]

Pompeii was literally buried in a matter of hours, so that’s kind of a unique case. Any underground structures would be turned into a cave from water seeping in. Most people don’t dig into the side of caves, so it’s likely we’d never know. A great example is the millennium old water passages in Afghanistan. You can’t tell they are man made any more.

The point stands, most things don’t survive all that long (in the grand scheme of things). Occasionally, the conditions are exactly right to preserve something, but there is a limit.

[cubefox]

Structures / cities might also get buried within a few hundred years due to overgrowth.

[datavirtue]

Sufficient sized meteorite impact would melt the entire surface of the planet.

[jiggawatts]

That did happen — the Moon is theorised to have formed from the ejecta of a planet-sized impactor.

However, that happened very early in the history of the solar system, likely before life had a chance to start.

[K0balt]

On the timescale we are looking at coastal areas are completely destroyed or created and substantial destruction and renewal of crust occurs. No guarantee of anything being found at all.

[cubefox]

Dinosaur fossils also didn't have a guarantee of being found. It's all in the probability.

[K0balt]

If you flip a fair coin 1000 times I guarantee it comes up heads at least once. If you set a cup on a table I guarantee it won’t pass through the table, even though both the glass and the table are mostly empty space.

Those things also are all in the probability.

[rini17]

Stone does weather too. It either needs uninterrupted dry climate (not really possible for millions of years) or being placed inside a stable geological formation (we don't usually build that way).

[cubefox]

I'd bet stone weathers many orders of magnitude less than dinosaur bones.

[JumpCrisscross]

Fossils are stone. The porous bone that housed the minerals are long gone by the time we find them.

[cubefox]

We are talking about actual bones in living animals though, and those surely fossilize (preserve over eons) much more rarely than many civilizational artifacts.

[JumpCrisscross]

> those surely fossilize (preserve over eons) much more rarely than many civilizational artifacts

I don't think they would fossilise. It's a process specific to the porosity of organic tissue. They might be preserved, but the Cambridge paper explains why it’s unlikely they would last for a hundred millennia or more.

[benj111]

But we don't have any evidence for anything approaching civilisation, fair enough humans have been industrialised for 200 years, but they've been building to that point for 10s of 1000s of years.

[safety1st]

If there was a stone age dinosaur civilization that lasted for 10,000 years, what evidence of it would survive? We only even have one fossil of a dinosaur per 10,000 years of dinosaur history. They key idea is how sparse our fossil record is compared to the vastness of life's history. Plus we are talking about 100,000,000 years ago - the chance a flint or metal tool, or a stone building would survive that long and be found by us is zero or close to it.

[csomar]

It's also not far fetched. The only "remains" of the dinosaurs era are birds. These are smart animals that actually build their homes. It's possible that dinosaurs had and built homes and maybe had a small civilization.

[colordrops]

Another argument goes that they transcending to technology and form beyond what we can comprehend, covered their tracks, and left us be because we aren't interesting or to avoid interfering in our development. Perhaps our perception through the 5 senses and an understanding of reality as a physical universe of spacetime is just a short phase between being an animal and being a multidimension being.

[fsloth]

That’s basically a ”rapture” hypothesis. ”We can’t see them because of ancient technobabble sciencemagic lifted them to another realm”.

In otherwords this is a supernatural, not natural hypothesis.

In other words, that’s more of a religious rather than scientific hypothesis.

It’s cool to have inspiration from where-ever, the whole point of religion and art is that they don’t need to be scientific.

But one really shouldn’t confuse non-scientific inspiration with actual science. Confusing the two leads to arguments like earth is 6000 years old and god just faked all the fossil evidence etc.

[bmitc]

> In other words, that’s more of a religious rather than scientific hypothesis.

I get what you're getting at, but I don't think it's so clear cut. Religion is more about organizational beliefs than just beliefs. Many parts of science are pretty far fetched in terms of us only knowing a bit with a very tightly constrained perspective (humans sitting on Earth with limited technology in the Solar System in the Milky Way) but making leaping conjectures. So in fact, science and religion have some shared analogues. (C.f. Paul Feyerabend.)

Certainly, the hypothesis you replied to is incredibly far fetched. But I don't think it's religious. It's more fantasy.

[tiberious726]

It's not falsifiable, therefore not scientific

[bmitc]

To be clear, I didn't say it was scientific.

[K0balt]

TBF we are assuming that we universally know what toolness looks like. There easily could be other forms of or paths to technology that we are completely ignorant of, even to the point of being ignorant of our ignorance.

[Izkata]

A much less out-there version was in Star Trek, they built spaceships and left, bringing most/all of their civilization with them. That version was just treated as lost history, with whatever may have been left behind simply not having been found yet or having decayed over such a long time period.

[Ekaros]

Big issue with this is would any species care to do that? To clean up planet used for years, decades or centuries by decent population would be massive undertaking. Probably magnitudes bigger than getting there in first place...

[colordrops]

Downvoters; I'm not arguing for this, just mentioning one of the arguments I've heard. I was going to be explicit about this and it looks like I should have been.

[mock-possum]

Yeah that’s more of a sci-fi plot than an argument.

[DrSiemer]

Isn't it one of the more likely answers to the Fermi paradox? "Transcending" could also be "everyone got really into VR and stopped caring about actual reproduction".