Fossilization is the process by which organic materials, like plants and animals, are preserved over time. This usually occurs when these materials are buried under layers of sediment, which protects them from decay. Over thousands or millions of years, minerals in the surrounding sediment can replace the original organic material, turning it into a fossil. There are different types of fossils, including trace fossils, which show evidence of an organism's activity, and body fossils, which are the actual remains of the organism. Fossilization helps scientists learn about the history of life on Earth and the evolution of different species.