3 methods of dating rock automatic software updating
The scheme has a range of several hundred thousand years.18.3.6 Radiocarbon Dating Method Radiocarbon dating, or carbon dating, is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 60,000 years.Carbon-14 is a radioactive isotope of carbon, with a half-life of 5,730 years, which is very short compared with those above.The neutrons resulting from the cosmic ray interactions participate in the following nuclear reaction on the atoms of nitrogen molecules (N2) in the atmosphere: The highest rate of carbon-14 production takes place at altitudes of 9 to 15 km, and at high geomagnetic latitudes, but the carbon-14 spreads evenly throughout the atmosphere and reacts with oxygen to form carbon dioxide.Carbon dioxide also permeates the oceans, dissolving in the water.In addition, there are trace amounts of the unstable isotope carbon-14 (14C) on Earth.
After plants die, or after they are consumed by other organisms, the 14C fraction of this organic material declines at a fixed exponential rate due to the radioactive decay of 14C.
18.3 Modern Dating Methods Radiometric dating has been carried out since 1905, and since then the techniques have been greatly improved and expanded.
Dating can now be performed on samples as small as a billionth of a gram using a mass spectrometer.
Atmospheric nuclear weapon tests almost doubled the concentration of 14C in the Northern Hemisphere.
Carbon has two stable, non-radioactive isotopes: carbon-12 (12C), and carbon-13 (13C).
For approximate analysis it is assumed that the cosmic ray flux is constant over long periods of time; thus carbon-14 is produced at a constant rate and the proportion of radioactive to non-radioactive carbon is constant: ca. For the most accurate work, local variations are compensated by means of calibration curves.