But maybe you are right and every dose of radiation even the one from the sun kills us over time. I mean, the skin of older people is not as clean as the one from young people. There are growing a lot of dark spots and bumps. Maybe this is life. Maybe it would be better to have fur like animals have.
LOL. This is not the reason why skin gets older. This is a Kent Hovind Theory.
(Also, this would imply that moles don't get elder, as they aren't exposed to the sun
)
A "harmless dose" is afaik a dose that isn't too much higher than the radiation that surrounds us all the time or a dose that kills less than very a small percentage of people exposed to it.
I haven't heard about marking the gulf stream so far, but I certainly know that they do the same to mark blood in a human's body to see if there are any areas without enough blood and stuff. This is "harmless" meaning that it most propably won't kill you (and not doing it would rather kill you if you are really sick), but doing it too often would of course increase the risk.
