Here’s more information on the subject. These experiments were some of the first to use isotopic tracers in biology. It’s now standard methodology.
p.s. That creek is completely dried up as I write this. I live in the upper Midwest, which is in the midst of a horrific drought.
Never mind “Once breathed by Caesar”. Consider Caesar’s last breath. John Allen Paulos calculated that there is a 98% chance that your last breath contains at least one molecule from Caesar’s last breath. http://econ161.berkeley.edu/movable_type/archives/001392.html
Admittedly the author assumes that only a trivial share of molecules were vented to outer space or sea or the Earth.
Decent username/post combo right here.