1. Fossil Fuels

2. Fuel
A fuel is a substance that provides energy; such as heat, light, motion, or electricity.
The change from one form of energy to another is called energy transformation. When fuels are burned, the chemical energy that is released can be used to generate another form of energy, such as heat, light, or electricity.
The process of burning a fuel is called combustion.

3. Fossil Fuels
Most of the energy used today comes from fossil fuels. Fossil fuels are the energy-rich substances formed from the remains of once-living organisms. Layers of sand, rock, and mud buried the dead organisms. Over millions of years, heat and pressure changed the materials into fossil fuels.
The three major fossil fuels are coal, oil, and natural gas.

4. Hydrocarbons
Fossil fuels are made of hydrocarbons. Hydrocarbons are energy-rich chemical compounds that contain carbon and hydrogen atoms.

5. Fossil Fuels
Coal is a solid fossil fuel formed from decaying plant matter. It is considered to be the most plentiful fossil fuel in the United States. However, coal mining can cause erosion and water pollution. When burned, most types of coal cause more air pollution than other fossil fuels.
Oil is thick, black liquid fossil fuel. Also known as petroleum, oil is formed from the remains of small animals, algae, and protists. Most oil deposits are located deep below Earth’s surface.

6. Fossil Fuels
Natural gas is a mixture of methane and other gases. Natural gas forms from the same organisms as oil. Because it is less dense, natural gas often rises above an oil deposit, forming a pocket.
Natural gas produces lower levels of many air pollutants than coal or oil and is fairly easy to transport. Natural gas is highly flammable, so a leak can cause a violent explosion or fire.

7. Fossil Fuels as part of the Carbon Cycle
Plants use carbon dioxide and sunlight to make their own food and grow. The carbon becomes part of the plant. Plants that die and are buried may turn into fossil fuels made of carbon (like coal and oil) over millions of years.
When humans burn fossil fuels, most of the carbon quickly enters the atmosphere as carbon dioxide.

8. CO2 and the Carbon Cycle
CO2 is a large part of the carbon cycle. Remember: the carbon cycle follows carbon's path from the air, to living organisms, then into dead organic matter, into the oceans, and then back into the atmosphere.

9. Balancing the Carbon Cycle
Scientists describe the cycle in terms of sources (parts of the cycle that add carbon to the atmosphere) and sinks (parts of the cycle that remove carbon from the atmosphere).
The key to balancing the carbon cycle is to make sure that you have the same amount of CO2 in your sources and your sinks.

10. Carbon Footprint
Everyone has a carbon footprint – the total amount of greenhouse gases produced to directly and indirectly support human activities, usually expressed in equivalent tons of carbon dioxide (CO2).
Your carbon footprint is the sum of all emissions of CO2, which were induced by your activities in a given time frame.
The carbon footprint is a very powerful tool to understand the impact of personal behavior on global warming. If you personally want to contribute to stop global warming, the calculation and constant monitoring of your personal carbon footprint is essential.

11. Typical Household Carbon Footprint

12. Nonrenewable Resources
People currently rely heavily on fossil fuels. But since fossil fuels take hundreds of millions of years to form they are considered nonrenewable resources. Fossil fuels are being used at a rate faster than they are formed. New sources of energy are needed to replace the decreasing fossil fuel reserves.
New energy sources will also help protect our environment by keeping our carbon cycle in balance.