What evolutionary significance, if any, does this have?

Coal is formed when layers of plant matter accumulate at the bottom of a body of water and are protected from biodegradation and oxidization. Over time, the properties of the original material change. What evolutionary significance, if any, does this have? It is a form of fossil fuel that can be used for generating energy. It is a form of fossilized plant and can be used to study the plants that lived at the time. It does not have any evolutionary significance.