What is the Fossil Record?
The "fossil record" refers to the placement of fossils throughout the surface layers of the Earth. Older fossils are buried more deeply than younger ones. Scientists use the placement of fossils as a guide for determining when life forms existed, and how they evolved. For example, we know that flowering plants evolved from non-flowering plants because, in the fossil record, we see flower fossils becoming more and more primitive the deeper we go, until they disappear all together. There are no flower fossils below a certain depth. This shows us that flowering plants evolved from non-flowering plants, then began to diversify themselves. This kind of progression is found throughout the fossil record.
[ References: Wikipedia: Fossil Record ]