Zircon is especially useful because it frequently contains uranium in substitution for zirconium, but does not incorporate lead (as shown by the absence of Lead-204).
Thus all the lead in the zircon can be assumed to be radiogenic.
Lava (properly called magma before it erupts) fills large underground chambers called magma chambers.
Most people are not aware of the many processes that take place in lava before it erupts and as it solidifies, processes that can have a tremendous influence on daughter to parent ratios.
Most scientists today believe that life has existed on the earth for billions of years.
This belief in long ages for the earth and the existence of life is derived largely from radiometric dating.
These elements are usually present in constant (equilibrium) amounts in a sample, as long as the system remains closed.
A closed system is one in which there is no free exchange of elements in a material with the outside environment.
This age is computed under the assumption that the parent substance (say, uranium) gradually decays to the daughter substance (say, lead), so the higher the ratio of lead to uranium, the older the rock must be.Thus any of the radioactive isotopes and its lead daughter product can be used for dating, or a combination may be used.In addition, some of the longer-lived intermediate daughter products have uses in dating.If modern lead, for example, from marine sediments or modern basalts has the composition of lead in the Earth and if the lead in the troilite phase of iron meteorites has the composition of primordial lead, then a simple model yields about 4.6 billion years for the age of the Earth.This age is in good agreement with the age of the meteorites and the age of the Moon as determined independently.The uranium and thorium decay systems offer a multitude of radiometric dating options.