Radiometric dating and astronomical dating
Fourth, a specimen's contamination by carbon from surrounding soil, water, vegetation, and animal matter can seriously undermine accuracy of tests on a given sample.
Second, compared with many other radiometric elements, carbon 14 decays quickly.It is useless for dating anything older than about 50,000 years.Third, because carbon 14 forms from cosmic ray bombardment of nitrogen 14 (and decays back into nitrogen 14 through the release of beta particles, i.e., electrons) the effect of variations in cosmic radiation intensity (caused by altitude, depth below the earth's surface, and astronomical events) can be difficult to calibrate.However, this helium gas easily leaks out of the host minerals.Thus two age estimates can be calculated for these mineral grains—one based on radioactive decay of uranium to lead, and the other based on the rate at which the helium leaks out of the mineral grains.This could even be the case when the K-Ar and Ar-Ar analyses yield "dates" compatible with other radioisotopic "dating" systems and/or with fossil "dating" based on evolutionary assumptions.
Furthermore, there would be no way of knowing, because the Ar not from radioactive decay, except of course by external assumptions about the ages of the rocks.
So, the uranium had to be decaying extremely rapidly to supply sufficient polonium quickly enough to form the adjacent polonium radiohalos.
And finally, helium gas is a by-product of the radioactive decay of uranium within minerals.
There are certain kinds of atoms in nature that are unstable and spontaneously change (decay) into other kinds of atoms.
For example, uranium will radioactively decay through a series of steps until it becomes the stable element lead. The original element is referred to as the parent element (in these cases uranium and potassium), and the end result is called the daughter element (lead and argon).
The geologist simply measures the relative amounts of potassium-40 and argon-40 to date the rock.