Carbon dating beta decay
Carbon atoms are incorporated into plant tissue (by photosynthesis) then into animal tissue (by ingestion) in nearly the same ratio as in the atmosphere. The Earth's magnetic field, its history, origin and planetary perspective.
The ratios are consistent among species, and the slight (1-3%) differences can also be calculated from the ratio of C) decreases as the radiocarbon decays. Libby determined, one gram of pure carbon should produce about 14 (13.56) radioactive decays per minute.
The Beta-counting method detects the rate at which purified carbon decays. A rate of 7 decays/gram/minute would indicate an age of one half-life, or 5730 years old.
3.5 decays/gram/minute of carbon would be produced by a sample 11,460 years old.
Both methods rely on the ongoing production of radiocarbon in the upper atmosphere.
At any particular time all living organisms have approximately the same ratio of carbon 12 to carbon 14 in their tissues.
This bomb radiocarbon has been gradually removed from the atmosphere by by natural processes, but the "bomb spike" can be shown through the dating by means such as comparing the bottle date and radiocarbon age of wines.
The surplus "bomb" radiocarbon is just one of the effects human have had on the ratio of C.
Many isotopes have been studied, probing a wide range of time scales.
C and counting the amount of each) allows one to date the death of the once-living things.
The rate of bombardment is greatest near the poles, where the Earth's magnetic field is dipping into the Earth and therefore does not deflect incoming cosmic rays.