Natural resources occur naturally and include materials like rocks, minerals, soil, rivers, plants and animals. They satisfy human needs and can be characterized by the biodiversity and geodiversity of the ecosystems they are found in. Humans are also considered a resource because through developing skills, they can add value to physical materials. Natural resources have economic, legal and aesthetic value and can be biotic, abiotic, renewable or non-renewable. They are forms of matter or energy found in nature and used by living things.