I’v posited in a thread or two about the difficulty of technology arising too early in the earth’s history, because at some point you’d have little in the way of oil, or coal, as a bridge to more advanced ways of generating power.

Here’s another related topic

https://www.cnn.com/2026/07/25/climate/silurian-hypothesis-another-civilization-before-humans?

“If an advanced civilization had lived on Earth millions of years ago, powered themselves with energy and wiped themselves out, would we know? Would they have left traces of their presence etched into the record of our planet?”

It looks like they looked at several lines of evidence that might show up, or would be easy to miss. Tectonic activity would mask/erase some evidence, and if we think in three dimensions, much of our planet is unexplored.

The Silurian Hypothesis

https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/silurian-hypothesis-would-it-be-possible-to-detect-an-industrial-civilization-in-the-geological-record/77818514AA6907750B8F4339F7C70EC6

I wonder about what might be missing, or changed from what we’d expect - missing oil and coal deposits where you’d expect, or nuclear waste, which would not have the natural isotopic abundances, regardless of whether it was still radioactive (not necessarily in some identifiable container, though you’d expect they’d have used one). That would include finding depleted uranium. (along the lines of evidence of the natural reactor found at Oklo)

The paper mentions the possibility of finding markers of a society that had a nuclear-weapons exchange

Given the maturity of technologies we now have for chemical analysis back to Archaean times (e.g. Organic geochemical evidence for life in Archean rocks identified by pyrolysis–GC–MS and supervised machine learning), it will become increasingly difficult for evidence of such civilisations to stay hidden.

The challenge remains that it only takes one measurement to confirm a presence: Haldane's Precambrian rabbits spring to mind. Proof of absence can never be absolute.

1 hour ago, swansont said:

The paper mentions the possibility of finding markers of a society that had a nuclear-weapons exchange

Seems to me if this had ever happened, it would leave a mark worldwide that could be found in nearly any layer of sedimentation from that time. Pretty interesting article, tho, and gives a pretty clear process for how and what to look for.

8 minutes ago, npts2020 said:

Seems to me if this had ever happened, it would leave a mark worldwide that could be found in nearly any layer of sedimentation from that time. Pretty interesting article, tho, and gives a pretty clear process for how and what to look for.

But how widespread is that, and how easily is it erased by geological processes if it happened 100-200 million years ago?

IOW, what evidence are we leaving behind that will survive that long, and what is the spatial extent of that? As the article points out, urban areas make up only ~1% of the earth’s surface area

9 minutes ago, swansont said:

But how widespread is that, and how easily is it erased by geological processes if it happened 100-200 million years ago?

IOW, what evidence are we leaving behind that will survive that long, and what is the spatial extent of that? As the article points out, urban areas make up only ~1% of the earth’s surface area

Of course it would take them having used anything that lasts that long but you have isotopes produced in a nuclear blast that would be detectable for that long. Plutonium-244, for example, has a half life of over 80 million years and is extremely rare naturally.

The 1st episode of the 4th ( and final ) season of Star Trek: Strange New Worlds has an interesting premise.
The ship is sent back in time to find a thriving Martian civilization 65 Million years ago.
They are at war with the arachnid inhabitants of the 5th planet ( not Jupiter ) and Earth is populated by Saurian species.
The Martian commander steals some of their anti-matter, and uses it to destroy the 5th planet leaving only asteroids.
One of the asteroids lands on Earth ( Yucatan peninsula ) and kills off the Dinosaurs, making way for mammals and humans.
The gravitational turbulence from the 5th planet's destruction shifts orbits, and Mars eventually becomes lifeless.
( wonder where the Martians went ? )

The point is that 65 Million years is a long time, never mind double or triple that.
And we have only made lasting 'markers' during the last few thousand years.

Edited 2 hours ago2 hr by MigL

2 hours ago, swansont said:

posited in a thread or two about the difficulty of technology arising too early in the earth’s history, because at some point you’d have little in the way of oil, or coal, as a bridge to more advanced ways of generating power.

Here’s another related topic

I've thought about this a bit FTtT, and tried to question every assumption we might make about what trajectory a technodevelopment takes. (Also, from a more SF angle, how technodevelopment might happen on a metal-poor planet) I don't know if there are many paths for alt-tech cultures to leapfrog fossil fuel use, though I guess it's impossible to rule out some kind of "artisan science" path which relies somewhat less on brute-force industrial revolution - say, still managing to smelt smaller amounts of metal, tinker with chemicals and make batteries, etc. Without mass production, I would think things like generators (from wooden windmills or water wheels) and devices that could run on them, would be more novelties, perhaps part of special exhibitions. The expense of smithy-produced copper, e.g., would mean that specialty electrical devices would tend to cluster around windmills or dams, as it would be too expensive to develop grids. There might be science colonies, widely separated places where people might flock in from the countryside to observe the wizardry, paying a fee to support it. If the Silurians had something like that, they might attain something which left no trace, as large-scale alterations of the planet would be beyond them, and certainly they'd be unable to develop nuclear technology or industrial-scale chemistry which can leave more longterm footprint. We'd be unlikely to find a copper-wound armature, i.e. EM coil, or anything like that.

High tech industrial society, however, would seem to inevitably leave traces not hard to find, as @npts2020 suggested. Having just watched a cat bury her product in the litter box, I do wonder how well tectonic action could disperse, grind up, and effectively hide the tech traces. Dispersal would be especially relevant to the ease of random discovery. Would there be preserving bubbles formed around some tech objects by, say, volcanic events like an ash fall or sudden lava inundation? E.g. could a reactor core, encased in ashfall, in the middle of a stable plate, remain fairly together in one lump?

Didn't the authors pick the wrong geological period ?

the Silurian was 425 MYA

This is long before the Carboniferous period produced the coal and oil we find today.

Isotopes are mentioned as possible tell-tales.

We do that already to distinguish between volcanic eruptions and meteorite impacts with extra terrestrial irridium.