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Carbon dating depends on the details of the biosphere. C14 is produced in the upper atmosphere by cosmic rays, and then (once it's fixed into a tree) it decays
by tlb 7y ago
Carbon dating depends on the details of the biosphere. C14 is produced in the upper atmosphere by cosmic rays, and then (once it's fixed into a tree) it decays with a half-life of 5700 years.
So if a chair is made of wood with a C14 fraction that's 1/4 of the atmospheric fraction, you can say it's 11400 years old (as a first-order approximation -- the actual science calibrates out a lot of things.)
But it's not clear that the presence of life would affect the C14 ratio in the upper atmosphere. The fraction should be where the production rate (proportional to the cosmic ray flux and percentage of nitrogen) matches the decay rate (1/5700 / year)
- opportune 7y agoBut Mars also has an atmosphere (although thin) of CO2 exposed to cosmic rays, no? So we could determine if there is some sort of CO2->methane cycle by seeing if there is any appreciable amount of C14 in the methane we find on Mars? Apologies if that's a stupid question, I'm out of my element here
- tlb 7y agoC14 is actually produced from cosmic rays hitting nitrogen, not carbon. The impact turns a proton into a neutron. Both CO2 and CH4, once the chemical bond is made, only decrease in C14 fraction as it spontaneously decays. Astronomers are pretty good at deducing things from the few, imprecise measurements they can make from millions of miles away, so you should never rule out them being able to figure out something. But it'll depend on a lot of assumptions.
- emmelaich 7y ago> I'm out of my element here Nice