Many of these links also appear where appropriate below.James Hutton and William Smith advanced the concept of geologic time and strengthened the belief in an ancient world.
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.
Dating is not necessary to demonstrate that evolution is a fact.
Chronological sequence is all that is really required.
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.
The Carbon14 technique has been and continues to be applied and used in many, many different fields including hydrology, atmospheric science, oceanography, geology, palaeoclimatology, archaeology and biomedicine. Isochron methods avoid the problems which can potentially result during radiometric testing.
Be sure to see An Animated Isochron Diagram, or, Watching a Rock Age on an Isochron Diagram. Radiometric Dating from The Evolution Evidence Page.
See more information about "Strata" Smith and his original geologic map of England.