Forms the basis of archaeomagnetic dating
The transformation of archaeological dating that began around 1950 continues, but archaeologists may overlook the revolution in scientific dating that had already taken place in geology during the first half of the twentieth century; from this wider perspective, the emergence of radiocarbon dating may seem slightly less dramatic Accurate knowledge of the age of the Earth was of little direct help to archaeologists, but it emphasised the potential of scientific dating techniques.
The first half of the twentieth century witnessed similar progress that began with the dating of recent geological periods in which early hominids lived, and ended with the introduction of radiocarbon dating.
Cores extracted from ocean floor deposits reveal variations in oxygen isotopes in the shells and skeletal material of dead marine creatures, which reflect fluctuations in global temperature and the volume of the ocean.
The rate of decay of 14C, which has a half-life of 5730 (40) years, is long enough to allow samples of carbon as old as 70,000 years to contain detectable levels of radioactive emissions, but short enough for samples from periods since the late Stone Age to be measured with reasonable precision.
In contrast, dating the change of one form of amino acid to another is derivative because the rate of alteration varies, and is heavily dependent on the temperature and humidity of the context where the sample has been buried.
Bones, teeth and shells contain proteins that break down after death, and the most commonly investigated products of decomposition are amino acids.
Wood only survives under exceptionally wet or dry conditions, and large timbers must be recovered to provide sufficient rings for valid comparisons because they rely on patterns that accumulated over several decades.
The successful development in the early twentieth century of radiometric methods relying upon radioactive decay for dating geological periods offered hope that a similar technique might be found to give absolute dates for prehistoric archaeology.