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 Wednesday at 06:25 PM3 days 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.

4 hours ago, TheVat said:

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.

All it would have to do is sufficiently bury it, or make so that it’s covered in water. There aren’t that many places where we dig down too far.

2 hours ago, studiot said:

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.

It’s apparently a Dr. Who reference, in which the Silurians are an ancient reptilian race.

10 hours ago, swansont said:

All it would have to do is sufficiently bury it, or make so that it’s covered in water. There aren’t that many places where we dig down too far.

It’s apparently a Dr. Who reference, in which the Silurians are an ancient reptilian race.

The scientific term Silurian comes form the ancient tribe in Wales, called the Silures where Silurain rocks in Britain are to be found.

Silurian rocks in Britain formed 444 to 419 million years ago and are of global importance because the system's name comes from the Silures, an ancient Welsh tribe, and standard time units (like Wenlock and Ludlow) are defined from British locations. During this time, closing oceans and tropical shallow seas deposited mudstones, limestones, and volcanic ash.

Reading the Cambridge article, note there's a footnote.

We name the hypothesis after a 1970 episode of the British science fiction TV series Doctor Who where a long-buried race of intelligent reptiles ‘Silurians’ are awakened by an experimental nuclear reactor. We are not however suggesting that intelligent reptiles actually existed in the Silurian age, nor that experimental nuclear physics is liable to wake them from hibernation. Other authors have dealt with this possibility in various incarnations (for instance, Hogan, 1977), but it is a rarer theme than we initially assumed.

Re:

15 hours ago, swansont said:

All it would have to do is sufficiently bury it, or make so that it’s covered in water. There aren’t that many places where we dig down too far.

I see it's kind of a numbers game. Also in the mix is tectonic movements that cause uplift and exhumation, which can reverse some burials. And how widespread the Silurian civilization was, and what percent of land they used, and how much was in proximity to subduction zones, and so on.

I want to dig further (npi) into the possibilities of isotope anomalies, reading the paper a little more closely. I thought there was a good point there about how some industrial changes are self-limiting as societies, to survive, have to move back towards sustainability and hence less impact. Silurians could go crazy on Haber Bosch, bomb a lot of agricultural surface with nitrogenous fertilizers, but then shift towards something else that's better for the watershed. Etc.

The longer human civilization lasts, the larger the signal one would expect in the record. However, the longer a civilization lasts, the more sustainable its practices would need to have become in order to survive. The more sustainable a society (e.g. in energy generation, manufacturing or agriculture) the smaller the footprint on the rest of the planet. But the smaller the footprint, the less of a signal will be embedded in the geological record. Thus, the footprint of civilization might be self-limiting on a relatively short timescale...

Back in 1981 a German SciFi novel called ‘Der Letze Tag der Schöpfung’ by Wolfgang Jeschke was first published, and was translated into English a year later  as ‘The Last Day of Creation’.

https://en.wikipedia.org/wiki/The_Last_Day_of_Creation

The opening part of the novel deals with the topic of temporal anachronisms i.e. the discovery of anomalous artefacts identifiable as fragments of a high technology recovered from parts of the ancient geological record where they had no right be.

In a number of cases these objects were first discovered during the middle ages or earlier, and had been preserved and venerated by the Catholic church as the relics of saints. In a pre-scientific era, such artefacts were so far beyond the comprehension of those who discovered them, that they were often treated as examples of a Xoanon - a Greek word for a cult object or statue belonging the gods and fallen to earth from heaven.

‘The Last Day of Creation’ isn’t predicated on a Silurian hypothesis: it’s actually to do with the possibility of time travel - but I won’t offer further spoilers in case anyone wants to read it.

The relevance here I suppose lies in the difficulty of even recognising any puzzling remanent of an ancient technology for what it is. One example that comes to mind was an unrusted iron dagger discovered in 1925 by Howard Carter inside the burial wrappings of the Egyptian pharaoh Tutenkhamun which puzzled archaeologists enormously.

https://www.bbc.co.uk/news/world-middle-east-36432635

Tutenkhamun died around 1323 BC and was mummified over 3,300 years ago, but the Iron Age did not begin until around 1200 BC -  so you have an apparent anachronism The explanation is that the ancient Egyptians used iron ore taken from a meteorite -  as was established in 2016 when scientists found that the iron blade contained high levels of nickel and cobalt similar to those found in another meteorite that had landed in northern Egypt in prehistoric times.