Here is one example of an isochron, based on measurements of basaltic meteorites (in this case the resulting date is 4.4 billion years) [Basaltic1981, pg. Skeptics of old-earth geology make great hay of these examples.
For example, creationist writer Henry Morris [Morris2000, pg.
I believe that many educated Christians are especially doubting the Bible because of the supposed evidence from radiometric dating that life has existed on earth for very long periods of time.
In fact, I believe that the question of how long life has existed on earth is even more important than the question of whether life was created or evolved.
Although the time at which any individual atom will decay cannot be forecast, the time in which any given percentage of a sample will decay can be calculated to varying degrees of accuracy.
The time that it takes for half of a sample to decay is known as the half life of the isotope.
Various elements are used for dating different time periods; ones with relatively short half-lives like carbon-14 (or C) are useful for dating once-living objects (since they include atmospheric carbon from when they were alive) from about ten to fifty thousand years old. Longer-lived isotopes provide dating information for much older times.The latest high-tech equipment permits reliable results to be obtained even with microscopic samples.Radiometric dating is self-checking, because the data (after certain preliminary calculations are made) are fitted to a straight line (an "isochron") by means of standard linear regression methods of statistics.Other radiometric dating methods such as potassium-argon or rubidium-strontium are used for such purposes by those who believe that the earth is billions of years old.Radiocarbon is not suitable for this purpose because it is only applicable: a) on a time scale of thousands of years and b) to remains of once-living organisms (with minor exceptions, from which rocks are excluded).