a source of energy made from the remains of ancient, once-living things

something that is found in nature and is valuable to humans

a natural material or source of energy that is useful to people and cannot be replaced easily

any harmful substance that affects Earth's land, air, and water

to refill, resupply, or to make complete again

a source of energy other than the burning of a fossil fuel

plant and animal wastes that can be processed to make fuel

the process of changing biomass into fuel

energy derived from the heat in the interior of the earth

electricity made by water power

converting energy from the Sun into electrical power

a useful material that is replaced quickly in nature