However, human beings love to see factual precision, and we want to know how old something is.Please remember that all dating methods, even those termed "absolute," are subject to margins of error. That is a very small amount of possible error range. Modern studies almost always use two or more methods to confirm dating work and to build confidence in the results obtained.A short but clear explanation about radioactive isotopes commonly used for determining ages of rocks (with graphics) and putting numbers on the geologic time scale, extending it back before the occurance of abundant index fossils.This is a relatively new method intended to to improve the precision of uranium and thorium istopy methods.Using these key or index fossils as markers, Smith could identify a particular layer of rock wherever it was exposed.Because fossils actually record the slow but progressive development of life, scientists use them to identify rocks of the same age throughout the world.This is made up of numerous regional tree-ring chronologies, particularly in the medieval and post-medieval periods, for which the laboratory now has more than 200 reference chronologies from many areas. By comparing the proportion of K-40 to Ar-40 in a sample of volcanic rock, and knowing the decay rate of K-40, the date that the rock formed can be determined.
These tests have been performed on what are thought to be the earth's oldest surviving rocks, meteorites, and moon rocks.Hutton, a Scottish geologist, first proposed formally the fundamental principle used to classify rocks according to their relative ages.He concluded, after studying rocks at many outcrops, that each layer represented a specific interval of geologic time.Dating is not necessary to demonstrate that evolution is a fact.Chronological sequence is all that is really required.