- Non-renewable resources are resources that cannot be replaced within a human generation, although some can be replaced over very long geological periods. Fossil fuels, metals and the element uranium, used to produce nuclear energy, are examples of non-renewable resources. Deposits of fossil fuels or metals are expected to eventually be replaced over millions or billions of years, but these rates of renewal are considered too slow to offset the rate at which resources are being depleted.
- Renewable resources are resources that can be replenished within one human generation, or about 20 to 30 years. Timber and food are renewable resources, because other trees or plants can be grown to replace any that are removed. Solar power, hydroelectric power and wind power are examples of renewable energy resources.
- Non-renewable resources are not an ideal source of energy because they exist in finite amounts and create pollution. Oil, coal and natural gas create harmful chemicals such as carbon monoxide when burned to produce energy. Extracting these resources can also be harmful to the environment, such as when large open-pit mines are created to mine coal, or when oil spills as a result of an accident in a pipeline or oil tanker.
- Renewable resources, including the sun, water and wind, can help the environment by creating less pollution than non-renewable energy sources. Renewable resources are not, however, an ideal source of energy either. For example, harnessing solar and wind energy requires a lot of space, and hydroelectric dams can destroy wildlife habitat. With continued research and development, however, renewable resources may one day replace non-renewable resources as the world's primary sources of energy.