The ratio of calcium formed to argon formed is fixed and known.
These radionuclides—possibly produced by the explosion of a supernova—are extinct today, but their decay products can be detected in very old material, such as that which constitutes meteorites. The uranium content of the material can then be calculated from the number of tracks and the neutron flux. If the same result is obtained sample after sample, using different test procedures based on different decay sequences, and carried out by different laboratories, that is a pretty good indication that the age determinations are accurate. On the other hand, the concentration of carbon falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades. Carbon is naturally in all living organisms and is replenished in the tissues by eating other organisms or by breathing air that contains carbon. Lunisolar Solar Lunar Astronomical year numbering. At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes.