Carbon-14 Dating - an example
C-14 is being constantly formed in the upper atmosphere by cosmic ray interactions with nitrogen. The balance of C-14 formation and decay results in a constant pool of C-14 in the atmosphere. Since living systems are constantly cycling carbon, all living organisms maintain an equilibrium level of C-14 in their tissues as long as the organism is alive.
Once an organism dies, the relative amount of C-14 declines by 50% for every 5730 years - the half-life of C-14. By measuring the relative amount of C-14 in a fossil, compared with modern material, the age can be calculated.
Complications emerged because our modern atmosphere has enhanced levels of C-14 as a result of open-air testing of atomic weapons between 1945 and the late 1960's, so actual standardization is done with pre-atomic testing samples, normalized to 1950. The major limitation of the technique is that after about 40,000 years, too little C-14 remains for accurate measurement. Dating of older rocks is accomplished using other isotopes (see above) which have half-lives long enough to date the age of the solar system.
C-14 is being constantly formed in the upper atmosphere by cosmic ray interactions with nitrogen. The balance of C-14 formation and decay results in a constant pool of C-14 in the atmosphere. Since living systems are constantly cycling carbon, all living organisms maintain an equilibrium level of C-14 in their tissues as long as the organism is alive.
Once an organism dies, the relative amount of C-14 declines by 50% for every 5730 years - the half-life of C-14. By measuring the relative amount of C-14 in a fossil, compared with modern material, the age can be calculated.
Complications emerged because our modern atmosphere has enhanced levels of C-14 as a result of open-air testing of atomic weapons between 1945 and the late 1960's, so actual standardization is done with pre-atomic testing samples, normalized to 1950. The major limitation of the technique is that after about 40,000 years, too little C-14 remains for accurate measurement. Dating of older rocks is accomplished using other isotopes (see above) which have half-lives long enough to date the age of the solar system.
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