Natural Gas –  is a fossil fuel formed when layers of buried plants and animals are exposed to intense heat and pressure over thousands of years. The energy that the plants originally obtained from the sun is stored in the form of carbon in natural gas. It is a nonrenewable resource because it cannot be replenished on a human time frame.  Natural gas consists primarily of methane.  In its refined state, it is often used for heating, cooking, and electricity generation, fuel for vehicles, etc.