Pb and cs dating
In two half-lives, half of the remainder will decay, meaning 3/4 in all will have decayed.In general, in n half-lives, only 1/(2^n) of the original parent material will be left.
The original element is called the parent, and the result of the decay process is called the daughter element.For potassium 40, the half-life is about 1.3 billion years.In general, in one half-life, half of the parent will have decayed.Perhaps the earth was made from older pre-existing matter, or perhaps decay rates were briefly faster for some reason. Geologic time is divided up into periods, beginning with the Precambrian, followed by the Cambrian and a number of others, leading up to the present.When one considers the power of God, one sees that any such conclusions are to some extent tentative. Some fossils are found in Precambrian rocks, but most of them are found in Cambrian and later periods.