Relative fossil dating is different from absolute dating, in one important way: Absolute dating gives you a number (for example, carbon dating a fossil to 50 million years ago). Relative dating puts the fossil in context---what lived before it, and what lived after.
Relative dating relates fossils to events. These events may be paleontological (relating to ancient life, like dinosaur extinction); geographical (relating to earth and natural environment, like eruptions and the Ice Age); and archaeological (relating to ancient society and structures, like the appearance of the Maya).
Relative fossil dating of ancient species relies upon stratigraphy. This is the study of layers that make up the Earth's crust. Similar layers, thousands of miles apart, come from the same period. So, fossils in those layers come from the same period as well.
Also known as chronometric dating, absolute dating is a more recent advance than relative dating. It relies upon measurable rates of Carbon 14 and Potassium 40 to determining an age.
The Pleistocene time is one event, marked by the appearance of the mammoth and mastodon, wild horses, woolly rhinoceros and saber-tooth cats; also by the Ice Age. This era ended about 12,000 years ago. Relative dating contrasts human evolution with these events. Neanderthal humans had died out by the end of the Pleistocene, while modern man (Homo Sapien) dominated.
Relative dating gives us a time line and context for a species. Relative dating told us, long before carbon dating, that dinosaurs died out long before hominids (early humans) existed.