Carbon-14 has a half-life of 5730 years and would have long ago vanished from Earth were it not for the unremitting cosmic ray impacts on nitrogen in the Earth’s atmosphere, which create more of the isotope.
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.
The parent isotopes have been decaying since they were formed in the stars, and so any parent isotope with a short half-life should be extinct by now. It is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere.
Closure temperatures are so high that they are not a concern.Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample.The carbon–14 dating limits lie around 58,000 to 62,000 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.
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.
18.3.5 Uranium-Thorium Dating Method A relatively short-range dating technique is based on the decay of uranium-238 into thorium-230, a substance with a half-life of about 80,000 years.
It is accompanied by a sister process, in which uranium-235 decays into protactinium-231, which has a half-life of 34,300 years.
An error margin of 2–5 % has been achieved on younger Mesozoic rocks.