“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?
I thought radiometric dating and low-background steel "prove" there were no nuclear detonations prior to WW2?