@futurebird on another note, we don't remember who wrote it but there was a short story once about time travelers who attempt to rob the library of Alexandria right before it burns down, but get caught by local law enforcement, who correctly deduce they're time travelers because......... they attempt to pass coins that are real gold, but all identical rather than showing individual variation in their manufacture

@ireneista @futurebird love that the local authorities were wise to time travel even back in the day

@futurebird though you wouldn't be able to tell when they were from specifically, and there would be plenty of "regular" explanations such as them having had unusual exposure to radiation during their life

@ireneista @futurebird
there are at least 4 different sources of natural C14 variations; high solar activity results in more cosmic rays striking the upper atmosphere, resulting in more C14, skewing dates slightly older. Low solar activity does the opposite. Similarily, up and down variations in magnetic field or ozone layer also cause C14 variations. Large scale fires of coal, oil, and gas deposits can occur naturally, and inject large amouts of old carbon that doesn't contain any C14.

@futurebird

Microplastics?

I do remember one science fiction story where a human fossil was obviously a time traveller, because:

A) a human skeleton was found in Cretaceous rock, 60 odd million years before anything human evolved

B) the scientist studying the fossil compared an x-ray of the unique pattern of bumps inside the skull, and found a modern human who matched 100%...himself.

@llewelly @futurebird oh that is fascinating. thank you for the detail!

@ireneista @futurebird
note that some trees, some corals, and some clams all make regular growth rings that are effectively "dead" after being made, and these can be counted up and used to measure year-on-year variations in carbon 14. Those resulting records of carbon 14 variations are used to interpret carbon 14 radiometric dates.

@ireneista @futurebird
there are at least 4 different sources of natural C14 variations; high solar activity results in more cosmic rays striking the upper atmosphere, resulting in more C14, skewing dates slightly older. Low solar activity does the opposite. Similarily, up and down variations in magnetic field or ozone layer also cause C14 variations. Large scale fires of coal, oil, and gas deposits can occur naturally, and inject large amouts of old carbon that doesn't contain any C14.

If a person were a time traveler how might that show up in their skeleton, eg in the isotopic analysis of their teeth?

@futurebird Great question, with no non-fictional answer because time travel is not possible

@futurebird Fluorine in the teeth; dental work generally. (Orthodontics leave traces! Implants on titanium posts rather more so.)

The other thing is that this kind of thing is generally very coarse; "its diet was C4 plants" has been the result for jaguar skeletal remains. (They were ritual jaguars fed on corn-fed turkeys, far as anyone can tell.) Absolute proof of time travel would take something impossible at tech level like that titanium post.

If a person were a time traveler how might that show up in their skeleton, eg in the isotopic analysis of their teeth?

@futurebird real question: how would you tell an ant was a time traveler?