We need to exceed the background of 370 atoms of 244Pu per gram [1].
[1] https://journals.aps.org/prc/abstract/10.1103/PhysRevC.85.01...
EDIT: huh, should have known what was going to happen -.-'
I thought radiometric dating and low-background steel "prove" there were no nuclear detonations prior to WW2?
“Many radioactive isotopes that are related to anthropogenic fission or nuclear arms, have half-lives that are long, but not long enough to be relevant here. However, there are two isotopes that are potentially long-lived enough. Specifically, Plutonium-244 (half-life 80.8 million years) and Curium-247 (half-life 15 million years) would be detectable for a large fraction of the relevant time period if they were deposited in sufficient quantities, say, as a result of a nuclear weapon exchange. There are no known natural sources of 244Pu outside of supernovae” [1].
Attempts have been made to detect primordial 244Pu on Earth with mixed success (Hoffman et al., Reference Hoffman1971; Lachner et al., Reference Lachner2012), indicating the rate of actinide meteorite accretion is small enough (Wallner et al., Reference Wallner2015) for this to be a valid marker in the event of a sufficiently large nuclear exchange. Similarly, 247Cm is present in nuclear fuel waste and as a consequence of a nuclear explosion.”
TL; DR Absent nuclear war, we wouldn’t be able to find evidence of a past nuclear civilisation after a few million years. Even by way of radiometric dating. (Low-background steel deals with atmospheric radiation. That isn’t relevant on sub-geological time scales.)
[1] https://www.cambridge.org/core/journals/international-journa...
(BTW, if I understand correctly this probably isn't an argument against nuclear energy, since if you replaced every iodine atom in your body with this isotope you'd still probably be within safe limits for radiation exposure, and more so if our descendants evolved to tolerate it as it gradually accumulated in the environment over millions of years.)
Seems to be running wild already [1]. Unclear if, due to it being naturally occurring, that would be a definitive signal.
The paper restricted itself to transuranic radioisotopes, but it’s unclear why. The operant question would be, if we found 129I on Mars, would that be evidence of technological civilisation?
Basically you are aware of the Silurian hypothesis and also the lost Mars civilization hypothesis. I’m guessing you also know of the recent cryptoterrestrial hypothesis [1] and how that might relate.
[1] https://www.researchgate.net/publication/381041896_The_crypt...
These are all admittedly fringe ideas but they have way more evidence and merit to them than people realize. reddit is a more appropriate place than HN to discuss these ideas because of the very speculative nature.
To rephrase your comments today are excellent contributions to such a discussion and if you haven’t already considered collecting them together and post on your favorite fridge sub and please let me know.
Thank you for your comments.
To be clear, I don’t buy these hypotheses. But they force us to ask questions that show the limits of our technology. If Mars had water 4 billion years ago, and an alien civilisation existed, my naïve guess is we’d find buried evidence of it. Weathering happens differently on Mars. But to know the answer is maybe not puts boundaries on what we can conclude from the data we find there, as well as our interpretation of our Fermi paradox observations.
I think you probably do subconsciously but you don’t want to admit it as they carry stigma which your background and training probably insists you avoid.
Im regards to Mars we have very little idea what is going on there. There is serious paper proposing fungi like life has already been observed but we haven’t recognized it. My understanding is a significant number of serious astro biologists think it’s likely there is currently life on Mars.
I’m definitely unaware of any archeological digs on Mars.
Since we are on the fringe topics I’ll mention that another related thought experiment is assume an advanced earlier Mars or Earth civilization moved to the Saturn system and currently resides there leveraging its abundant resources. Would we have actually detected it already?
“…for all the dinosaurs that ever lived, there are only a few thousand near-complete specimens, or equivalently only a handful of individual animals across thousands of taxa per 100,000 years. Given the rate of new discovery of taxa of this age, it is clear that species as short-lived as Homo sapiens (so far) might not be represented in the existing fossil record at all” [1].
> Wouldn’t tools and stuff also end up in the geological record
Corrode, break down, subsume into the mantle, et cetera.
[1] https://www.cambridge.org/core/journals/international-journa...
If you’re in California, you can go to Sharktooth Hill in Bakersfield to understand what that means. Million year old Megalodon teeth are plentiful and a few days digging is all but guaranteed to find several of them, among many other bones. The hard part is identifying the geological formations and excavating them while preserving context, which is impossible when its open to the public for digging. Once we’ve found the formations, it takes decades and decades because of a lack of funding and manpower (especially to assemble and research them).
Complete skeletons are especially rare because we haven’t had the technology to reassemble bone correctly until recently with surface proteomic analysis.
Source that might quantify that in terms of frequency?
> you can go to Sharktooth Hill in Bakersfield
Or Scott’s Valley or Capitola. There are a lot. Now consider how many clams or trilobites existed across those hundreds of millions of years.
Pushing back because I’ve never seen this prong of their hypothesis contested.
Keep in mind that most oceanic crust formed less than 200 Mya [1]. (Continents are better, clocking in at Ga timescales [2].)
[1] https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/200... Figure 1
[2] http://www.lithosphere.info/papers/2006-Tecto-Art-TC1-small.... Table 1
Obviously thats out of trillions of animals and only a tiny fraction of animals get fossilized and plenty of species never left a record, but at the human scale, we have so many freaking fossils we have no idea what to do with them. We bring our kids out on field trips to dig for them and leave with dozens of bones per kid that are at least hundreds of thousands of year old, because no one bothers if they're <10My old otherwise.
I’m not arguing that the fossil record is any more than a minuscule sliver of all animals that have ever lived, but there are still a lot of them and there’s no doubt human civilization is leaving its own behind that will be detectable millions of years from now.
Does that challenge that we only have fossils for “only a handful of individual animals across thousands of taxa per 100,000 years”?
Less than 0.1% of species wind up in the fossil record [1]. (I’ve heard but can’t reliably source 5% for animals.)
Most of those species existed far longer than we have. Hence why the astrophysicists who came up with the hypothesis ruled out fossils, much less fossils that would show evidence of industrial civilisation.
> no doubt human civilization is leaving its own behind that will be detectable millions of years from now
Sure, 2+ million, per the paper that sparked this.
[1] https://www.bbc.com/future/article/20180215-how-does-fossili...
Rigorously work out how long each of those components would last under even ideal natural circumstances. Silicon doesn't devitrify like glass. But it will weather away, atomically, chemically and physically.
They may have been around for 1000x longer than humans but the billions and billions of tons of gold, copper, and other native metals will be obvious non-degradable remnants that will survive us for hundreds of millions of years. Any metal that can be found in its native form will survive for a very, very long time and the list of such metals is long. We already know that stone tools from archaic human and apes easily survives for millions of years.
The Keweenaw copper deposits [1] where copper is mined in boules and nuggets far larger a strand of copper wire is about a billion years old. That's how long our bulk metal artifacts will survive, despite rigorous geological activity. Those artifacts already number in the hundreds of billions if not trillions. The only reason they don't already litter the planet like ancient pottery and arrow heads is that they're highly recyclable and reusable.
> But I expected HN’s responses to be a touch more thought through.
We've just been talking past each other which is par for the course for HN.
Scary if they didn't!
EDIT: what else killed them off or where did they go and will they come back, so it's actually quite curious and less scary but it made me shiver when I read it the first time.
You’re citing artefacts on the order of centuries to millennia. This is off by many orders of magnitudes from the paper’s subject. Arrowheads would not be expected to survive millions of years, thousands of times longer than they have to date. (EDIT: Obviously wrong.)
You’re right. 3.3mm [1]. Not evidence of “industrial civilisation,” though. And within the few million year guess the paper posited.
Those tools would have to be lucky to survive 10mm years. (The Earth is tearing itself apart not far from the site [2].) Our factories and cars would need more than luck.
[1] https://www.smithsonianmag.com/science-nature/oldest-known-s...
[2] https://www.sciencealert.com/there-s-mounting-evidence-the-c...
If something does not degrade biologically/chemically and is shielded from the elements it's going to take a long time to make it unrecognizable. We find biological fossils all the time. And they're old.
Put another way, if we found this rock in an old stratum, tens or hundreds of millions of years old, would it be proof someone with industry was there?
Gold jewelry, but I'm not sure it can prove industrialization.
The asphalt of the roads may dissapear, but the gravel mixed with it and under it will create a very strange pattern.
Panama and Suez channels, unless they are very unluck and get destroyed.
Kitchen granite top and tumbstones. Marble may disolve if there is and acid environment.
Quarries and coal mines are huge.
Million years [1]. (It devitrifies.)
> asphalt of the roads may dissapear, but the gravel mixed with it and under it will create a very strange pattern
Would this be recognisable at an industrial scale?
> Panama and Suez channels
Suez is right above the East African rift, so maybe 10 My. Panama no clue.
> Quarries and coal mines are huge
To where they could evidence industrial activity after millions of years?
[1] https://education.seattlepi.com/long-glass-bottle-degrade-la...
> Million years. (It devitrifies.)
Very interesting. It's difficult to get hard numbers. It depends a lot on the composition and the temperature, so I'm more optimistic about they lasting for a few millons years at burried at 15°C(60°F), but I agree they don't last forever
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>> asphalt of the roads may dissapear, but the gravel mixed with it and under it will create a very strange pattern
> Would this be recognisable at an industrial scale?
I guess so. We have a lot of roads with a not random patterns.
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>> Panama and Suez channels
> Suez is right above the East African rift, so maybe 10 My. Panama no clue.
I agree. Both are in bad positions to last forever.
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>> Quarries and coal mines are huge
> To where they could evidence industrial activity after millions of years?
I guess they are. Look at this video https://www.youtube.com/watch?v=fjp6RHb7MtE the truck are huge, from time to time there appears a normal truck next to them and it looks like a toy truck. I think when abandonded they get filled with water, then with mud and decomposing plants, and then that will solidify and in the future they will have a huge "volvano caldera" but no volcano at the bottom. Also find the internal roads, cuts by explossions and other strange characterisitcs. The truck will have rot a long time ago and dissapeared, but they may find unusual levels of iron contamination in the parking lot.
Same with steel, stainless steel, brass, ceramics (of all types), glass, plastic, etc.
Hell, just all the roadside glass bottles over the years will leave one difficult to ignore trail.
Iron oxide is super stable. Chromium oxide too.
I’m not saying they’ll not oxidize, I’m saying they’ll still form very recognizable, unnatural, and stable shapes when they do. Even a fully oxidized iron sword leaves a sword shaped lump where it is.
And that isn’t something that occurs very often in nature.
“If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today” [1]?
TL; DR Difficult after ~2.5 million years unless they had a nuclear war.
As for humans: “some specific tracers that would be unique” include “persistent synthetic molecules, plastics and (potentially) very long-lived radioactive fallout in the event of nuclear catastrophe. Absent those markers, the uniqueness of the [Anthropocene] may well be seen in the multitude of relatively independent fingerprints as opposed to a coherent set of changes associated with a single geophysical cause.”
Bonus: “…should any of the initial releases of light carbon described above indeed be related to a prior industrial civilization…these releases often triggered episodes of ocean anoxia (via increased nutrient supply) causing a massive burial of organic matter, which eventually became source strata for further fossil fuels. Thus, the prior industrial activity would have actually given rise to the potential for future industry via their own demise. Large-scale anoxia, in effect, might provide a self-limiting but self-perpetuating feedback of industry on the planet.”
So if we’re going out, we should go all the way and suffocate the oceans out of courtesy.
[1] https://www.cambridge.org/core/journals/international-journa...