Chemistry Reference
In-Depth Information
(continued)
About one atom in a few trillion carbon atoms is carbon
14, but these isotopes drift around and are taken up by liv-
ing organisms, including humans as they eat, and by plants
during photosynthesis. Some of the carbon 14 atoms decay
but are replaced during the organism's food intake. When
the organisms die, the carbon 14 in the body decays and is
not replaced. Measurements of the carbon 14 to carbon 12
ratio indicates how long the body stopped taking up carbon
14—or, in other words, how long ago the organism died. The
University of Chicago researcher Willard Libby developed this
procedure, called radiocarbon dating, in 1949.
Archaeologists widely use radiocarbon dating as a means
of dating organic material, but the technique has some cave-
ats. In order to determine how much the carbon 14/carbon
12 ratio has declined, archaeologists must know what this
ratio was at the time of the organism's death. The value of
this ratio should be roughly the same as the ratio in the at-
mosphere, but the atmospheric ratio of carbon 14/carbon
12 has changed slightly over time, so archaeologists must
take this change into account. The sample must not be con-
taminated with any new carbon, which could introduce more
carbon 14 and throw off the ratio. Radiocarbon dating is
also useful only for the recent past; beyond about 50,000
years, so much carbon 14 has decayed that the tiny resi-
due is almost impossible to measure accurately. Ötzi is well
within this range, for he died, in terms of carbon 14, only a
little less than one half-life ago.
wearing and aging of the teeth and bones. Although it is difficult to be
precise, Ötzi was about 40-45 years old at the time of his death. Con-
sidering the ravages of disease and the precarious existence of human
beings in this era, Ötzi was probably considerably older than many of
his contemporaries.
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