Here's why:

* Coal: Coal forms from the accumulation of plant matter in swampy environments. Over millions of years, layers of dead plants are buried under sediment and subjected to heat and pressure. This transforms the plant matter into coal.

* Petroleum: Petroleum forms from the remains of tiny marine organisms (plankton and algae) that die and settle to the bottom of the ocean. Over time, they are buried under layers of sediment, and heat and pressure transform them into hydrocarbons, which form crude oil and natural gas.

Key Points:

* Sedimentary rocks: These rocks are formed from the accumulation and cementation of sediments, such as sand, mud, and organic matter. They often form in layers.

* Fossil fuels: Coal and petroleum are considered fossil fuels because they are derived from the remains of ancient organisms.

Let me know if you have any other questions!