Why is the fossil record important in the theory of evolution?

The fossil record is crucial to the theory of evolution as it provides tangible evidence of the gradual changes in species over time, illustrating the process of descent with modification. Fossils reveal the existence of now-extinct organisms, helping scientists trace evolutionary lineages and understand how species adapted to their environments. Additionally, the fossil record can show transitional forms, which support the idea of common ancestry among diverse species. Overall, it serves as a key source of data for reconstructing the history of life on Earth.