Why is evoultion a theory not a law?

Evolution is a theory not a law because Scientists define evoultion as a change gene pool that population changes over time. This rate of evolution is all that is required to produce the diversity of the living things as common ancestors. The thoery of evolution says that life originated, and evolution proceeds by random chance. Evolution is a thoery not a law because in science a theory is a well explained explanation for some aspect of the world. Evoulion is a well substained fact because it has been observed and it explains the sequence and arrangement of fossil record. As well as scientific thoery descent with modication species share a common ancestor. Theres a fact of evolution that species there is a variation within one kind of animal.