The differences actually found in the scientific literature are usually close to the margin of error, usually a few percent, not orders of magnitude!
Vast amounts of data overwhelmingly favor an old Earth.
Radioactive decay rates have been measured for over sixty years now for many of the decay clocks without any observed changes.
None of these experiments has detected any significant deviation for any isotope used in geologic dating [Dalrymple1991, pg. Note, for instance, that light coming to earth from distant stars (which in some cases emanated billions of years ago) reflects the same patterns of atomic spectra, based in the laws of quantum mechanics, that we see today.The slope of the line determines the date, and the closeness of fit is a measure of the statistical reliability of the resulting date.Technical details on how these dates are calculated are given in Radiometric dating. As with any experimental procedure in any field of science, these measurements are subject to certain "glitches" and "anomalies," as noted in the literature.Other objections raised by creationists are addressed in [Dalrymple2006a].The overall reliability of radiometric dating was addressed in some detail in a recent book by Brent Dalrymple, a premier expert in the field. 80-81]: These methods provide valid age data in most instances, although there is a small percentage of instances in which even these generally reliable methods yield incorrect results.