How do Fossil fuels show evidence of evolution & What are the flaws of using Fossil fuels as evidence for evolution

HOW IT WORKS - Fossils of the simplest organisms are found in the oldest rocks, and fossils of more complex organisms in the newest rocks (supports Darwin's theory of evolution that life forms eventually formed into complex ones) FLAWS - There are gaps in the fossil record because many early forms of life were soft-bodied, which means that they have left few traces behind or traces destroyed due to geological activity