3 methods of dating rock
The mass spectrometer operates by generating a beam of ionized atoms from the sample under test.The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as “Faraday cups“, depending on their mass and level of ionization.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.Plants take up atmospheric carbon dioxide by photosynthesis, and are ingested by animals, so every living thing is constantly exchanging carbon-14 with its environment as long as it lives.One of its great advantages is that any sample provides two clocks, one based on uranium-235’s decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238’s decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in cross-check that allows accurate determination of the age of the sample even if some of the lead has been lost.18.3.2 Method This is based on the beta decay of rubidium-87 to strontium-87, with a half-life of 50 billion years.
The rate of creation of carbon-14 appears to be roughly constant, as cross-checks of carbon–14 dating with other dating methods show.
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.
However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon–14 and give inaccurate dates.
One of the most frequent uses of radiocarbon dating is to estimate the age of organic remains from archaeological sites.