Ever since recorded history began, and probably before, people have found pieces of rock and other hard material with indentations from the remains of dead organisms. These are called fossils, and the totality of these artifacts and their placement in rock striations is referred to as the fossil record.
The fossil record is one of the primary sources of data relevant to the study of evolution. They are examined by scientists in order to understand the process of evolution and the way specific species evolved.
Dating methods, such as radioactive carbon, show that some of these fossils are tens of millions of years old. Various dating methods have been used and are used today, and while there is some variance in the results from these dating methods, nearly all of them provide evidence for a very old Earth and evolution.
However, a few scientists and many non-scientists reject the authenticity of the fossil record, primarily on religious grounds. Those who accept Sudden Creationism, for example, completely reject the fossil record as evidence of evolution.
Not all Creationists reject the fossil record. The Intelligent Design theory, for example, embraces both the fossil record and natural selection, but says that speciation happens through God's intervention.
Therefore, the matter of the fossil record provides a clear but often overlooked distinction between the primary schools of thought within Creationism.