The number of protons in an atom determines which element it is, while the number of neutrons determines which isotope it is.For example, strontium-86 has 38 protons and 48 neutrons, whereas strontium-87 has 38 protons and 49 neutrons.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.Recent puzzling observations of tiny variations in nuclear decay rates have led some to question the science of using decay rates to determine the relative ages of rocks and organic materials.

For example, creationist writer Henry Morris [Morris2000, pg.An oversight in a radioisotope dating technique used to date everything from meteorites to geologic samples means that scientists have likely overestimated the age of many samples, according to new research from North Carolina State University.To conduct radioisotope dating, scientists evaluate the concentration of isotopes in a material.The unswerving regularity of this decay allows scientists to determine the age of extremely old organic materials -- such as remains of Paleolithic campfires -- with a fair degree of precision.The decay of uranium-238, which has a half-life of nearly 4.5 billion years, enabled geologists to determine the age of the Earth.