Natural resources can be a solid, liquid, or gas. They can also be organic, coming from living things, or inorganic, coming from a non-living source. All natural resources are also either renewable or non-renewable.

Renewable resources are always available and can be easily replaced or recovered. The examples of renewable resources include water, plants, animals, the sun, wind, and a few others. Most renewable resources may be replaced in a short period of time. For example, animals are renewable because they can reproduce young offspring replacing adult animals in a short period of time. If it takes too many years to replace a resource it is not considered to be renewable.

Non-renewable resources cannot be easily replaced once they are destroyed. Examples of these resources include fossil fuels such as coal, petroleum, oil, and natural gas. Non-renewable resources may take thousands or millions of years to be replaced. Minerals, though form naturally, are also non-renewable because the rock cycle used in replacing the minerals will take thousands of years. There are also some animals that can be non-renewable if they are in danger of becoming extinct.

Non-renewable resources cannot be easily replaced once______.