High School Earth Science/Nonrenewable Energy Resources

Have you ever seen dinosaur fossils at a museum? If so, you may have read about how the dinosaur bones turned into fossils. The same processes that formed these fossils also formed some of our most important energy resources. These resources are called fossil fuels. Fossil fuels provide a very high quality energy, but because of our demand for energy, we are using up these resources much faster than they formed.

Lesson Objectives

Describe the natural processes that formed different fossil fuels.
Describe different fossil fuels, and understand why they are nonrenewable resources.
Explain how fossil fuels are turned into useful forms of energy.
Understand that when we burn a fossil fuel, most of its energy is released as heat.
Describe how the use of fossil fuels affects the environment.
Describe how a nuclear power plant produces energy.

Formation of Fossil Fuels

As you might guess from their name, fossil fuels are made from fossils. Fossil fuels come from materials that began forming about 500 million years ago. As plants and animals died, their remains settled on the ground and at the bottom of bodies of water. Over time, these remains formed layer after layer. Eventually, all of these layers were buried deep enough that they were under an enormous mass of earth. The weight of the earth pressing down on these layers created intense heat and pressure.

After millions of years of heat and pressure, the material in these layers turned into chemicals called hydrocarbons, which are compounds of carbon and hydrogen. The hydrocarbons in these layers are what we call fossil fuels. The hydrocarbons could be solid, liquid, or gaseous. The solid form is what we know as coal. The liquid form is petroleum, or crude oil. We call the gaseous hydrocarbons natural gas.

You may be surprised to learn that anything that used to be alive could change enough to become something so different, such as coal or oil. There is enough heat and pressure deep below the earth's surface even to create diamonds, which are the hardest natural material in the world.

Like fossil fuels, diamond is made of carbon. In fact, diamond is a type of pure carbon, so it does not contain the hydrogen that fossil fuels do. What determines whether the remains of living things deep in the earth turn into coal, oil, natural gas, diamond, or something else? All of these materials form under high heat and pressure, but the conditions are different for each material.

Coal

Coal is the solid fossil fuel that forms from dead plants that settled at the bottom of swamps millions of years ago. The water and mud in the swamps affected how the remains of plants broke down as they were compressed. The water and mud in the swamp keep oxygen away from the plant material. When plants are buried without oxygen, the organic material can be preserved or fossilized. Then, other material, such as sand and clay, settles on top of the decaying plants and squeezes out the water and some other substances. Over time, the pressure removes most of the material other than carbon, and the carbon-containing material forms a layer of rock that we know as coal.

Coal is black or brownish-black in appearance. Coal is a rock that burns easily. Most forms of coal are sedimentary rock. But the hardest type of coal, anthracite, is a metamorphic rock, because it is exposed to higher temperature and pressure as it forms. Coal is mostly carbon, but some other elements can be found in coal, including sulfur.

Around the world, coal is the largest source of energy for electricity. The United States is rich in coal, which is used for electricity. California once had a number of small coal mines but the state no longer produces coal.

A common way of turning coal into a useful form to make electricity starts with crushing the coal into powder. Then, a power plant burns the powder in a furnace that has a boiler. Like other fuels, coal releases most of its energy as heat when it burns. The heat that the burning coal releases in the furnace is enough to boil the water in the boiler, making steam. The power plant uses this steam to spin turbines, and the spinning turbines make generators turn to create electricity.

For people to use coal as an energy source, they need to get it out of the ground. The process of removing coal from the ground is known as coal mining. Coal mining can take place underground or at the surface. The process of coal mining, especially surface mining, affects the environment. Surface mining exposes minerals from underground to air and water from the surface. These minerals contain the chemical element sulfur, and sulfur mixes with air and water to make sulfuric acid, which is a highly corrosive chemical. The sulfuric acid gets into nearby streams and can kill fish, plants, and animals that live in or near the water. The process of burning coal causes other problems for the environment. A little later, we will look at these other pollution problems, when we explore problems with fossil fuels in general.

Oil

Oil is a thick liquid that is usually dark brown or black in appearance. It is found mostly in formations of porous rock in the upper layers of the Earth's crust. Oil is currently the single largest source of energy in the world. How does oil form? The process of making oil is similar in many ways to the process of making coal. The main difference is in the size of the living things—the organisms—whose remains turn into these fossil fuels. The organisms that die and became the material for making oil are much smaller than the plants that turned into coal. These organisms are called plankton and algae. When the plankton and algae die, their remains settle to the bottom of the sea. There, they were buried away from oxygen, just as the plants did in the process of becoming coal. As layers of sediment pile on top of these decaying organisms, heat and pressure increase. Over a period of millions of years, the heat and pressure turn the material into liquid oil.

The United States produces oil, although only about one-quarter as much as it uses. The main oil producing regions are the Gulf of Mexico, Texas, Alaska, and California. Most of California's oil fields are in the southern San Joaquin Valley. Compression from when the region was a convergent plate boundary produced a set of anticlines that are parallel to the San Andreas Fault. Oil collects in permeable sediments that are capped by an impermeable cap rock. Oil is also pumped on and off the southern California coast.

Oil as it comes out of the ground is called crude oil. Crude oil is a mixture of many different hydrocarbons. Oil refining is used to separate the compounds in this mixture from one another (Figure 5.3). We can separate crude oil into several useful fuels because each hydrocarbon compound in crude oil boils at a different temperature. An oil refinery heats the crude oil enough to boil the mixture of compounds. Special equipment in the refinery separates these compounds from one another as they boil.

Figure 5.3: Refineries like this one separate crude oil into many useful fuels and other chemicals.

Most of the compounds that come out of the refining process are fuels. The rest make up waxes, plastics, fertilizers, and other products. The fuels that come from crude oil, including gasoline, diesel, and heating oil, are rich sources of energy that can be easily transported. Because of this, fuels from oil provide about 90% of the energy used for transportation around the world.

We get gasoline from refining oil. Like oil, gasoline is most commonly used for transportation because it is a concentrated form of energy that is easily carried. Let's consider how gasoline powers a car. Like other fuels you have learned about, gasoline burns and releases most of its energy as heat. When it burns, the gasoline turns into carbon dioxide gas and water vapor. The heat makes these gases expand, like the heated air that fills a hot-air balloon. The expanding gases create enough force to move pistons inside an engine, and the engine makes enough power to move the car.

When a resource like gasoline is concentrated in energy, it contains a large amount of energy for its weight. This is important because the more an object weighs, the more energy it takes to move that object. If we could only get a little energy from a certain amount of gasoline, a car would have to carry more of it to be able to travel very far. But carrying more gasoline would make the car heavier, so moving the car would take even more energy. So a resource with highly concentrated energy is a practical fuel to power cars and other forms of transportation.

Unfortunately, using gasoline to power automobiles also affects the environment. The exhaust fumes from burning gasoline include gases that cause many different types of pollution, including smog and ground-level ozone. These forms of pollution cause air-quality problems for cities where large numbers of people drive every day. Burning gasoline also produces carbon dioxide, which is a cause of global warming.

Natural Gas

Natural gas is a fuel that is a mixture of methane and several other chemical compounds. It is often found along with coal or oil in underground deposits. The conditions that create natural gas are similar to those that create oil. In both cases, small organisms called plankton and algae die and settle to the bottom of the sea. In both cases, the remains of these organisms decay without oxygen being present. The difference is that natural gas forms at higher temperatures than oil does.

The largest natural gas reserves in the United States are found in the Rocky Mountain states, Texas and the Gulf of Mexico region. California also has natural gas, mostly in the northern Sacramento Valley and the Sacramento Delta. In that region, a sediment filled trough formed aside an ancient convergent margin. Organic material buried in the sediments hardened to become a shale formation that is the source of the gas.

Because it is a mixture of different chemicals, natural gas must be processed before it can be used as a fuel. Some of the chemicals in unprocessed natural gas are poisonous to humans. Other parts, such as water, make the gas a less useful fuel. The processing removes almost everything but methane from natural gas. At this point, the gas is ready to be delivered and used.

Natural gas, often known simply as gas, is delivered to homes for uses such as cooking and heating. Many ranges and ovens use natural gas as a fuel, and gas-powered furnaces, boilers, water heaters, and clothes dryers are also common.

Natural gas is a major source of energy for powering gas turbines and steam turbines to make electricity. When it is used in this way, natural gas works similarly to the way coal does in producing energy for electricity. Like coal and other fuels, natural gas releases most of its energy as heat when it burns. The power plant is able to use this heat, either in the form of hot gases or steam from heated water, to spin turbines. The spinning turbines turn generators, and the generators create electricity.

Processing and using natural gas does have some harmful effects on the environment. Natural gas does burn cleaner than other fossil fuels, meaning that it causes less air pollution. It also produces less carbon dioxide than the other fossil fuels for the same amount of energy.

Problems with Fossil Fuels

Although they are rich sources of energy, fossil fuels do present many problems. Because these fuels are nonrenewable resources, their supplies will eventually run out. Safety can be a problem, too, because these fuels burn so easily. For example, a natural gas leak in a building or an underground pipe can lead to a deadly explosion.

Using fossil fuels affects the environment in a variety of ways. There are impacts to the environment when we extract these resources. There are problems that arise because we are running out of supplies of these resources. Burning these fuels can cause air pollution and burning them releases carbon dioxide, which is a major factor in global warming (Figure 5.4).

Figure 5.4: Coal power plants like this one release large amounts of steam and smoke into the air.

Many of the problems with fossil fuels are worse for coal than for oil or natural gas. Coal contains less energy for the amount of carbon it contains than oil or gas. As a result, burning coal releases more carbon dioxide than burning either oil or gas (for the same energy). And yet coal is the most common fossil fuel and so we continue to burn large amounts of it. Coal is the biggest contributor to global warming.

Another problem with coal is that it usually contains sulfur. When coal burns, the sulfur goes into the air as sulfur dioxide. Sulfur dioxide is the main cause of acid rain, which can be deadly to plants, animals, and whole ecosystems. Burning coal also puts other polluting chemicals and a large number of small solid "particulates" into the air. These particles are dangerous to people, especially those who have an illness, like asthma, that makes breathing hard for them.

Nuclear Energy

When scientists learned how to split the nucleus of an atom, they released a huge amount of energy. Scientists and engineers have learned to control this release of energy. The controlled release of this energy is called nuclear energy. Nuclear power plants use uranium that has been processed and concentrated in fuel rods (Figure 5.5). The uranium atoms are split apart when they are hit by other extremely tiny particles. Nuclear power (nuclear fission) is not the same as a nuclear bomb. Explosives cannot directly be made out of uranium, it has to be enriched with Plutonium. Therefore nuclear powerplants cannot explode, meltdown however can occur if the cooling system of the plant is interrupted.

Figure 5.5: Nuclear power plants like this one provide France with almost 80% of its electricity.

Nuclear power plants use the energy they produce to heat water. Once the water is heated, the process is a lot like what happens in a coal power plant. The hot water or steam causes a turbine to spin. When the turbine spins, it makes a generator turn, which in turn produces electricity.

Many countries around the world use nuclear energy as a source of electricity. For example, France gets about 80% of its electricity from nuclear energy. In the United States, a little less than 20% of electricity comes from nuclear energy.

Nuclear energy does not pollute the air. In fact, a nuclear power plant releases nothing but steam into the air. But nuclear energy does create other environmental problems. The process of splitting atoms creates a dangerous by-product called radioactive waste. The radioactive wastes produced by nuclear power plants remain dangerous for thousands or hundreds of thousands of years. So far, concerns about this waste have kept nuclear energy from being a larger source of energy in this country. Scientists and engineers are looking for ways to keep this waste safely away from people.

Lesson Summary

Coal, oil and natural gas are all fossil fuels formed from the remains of once living organisms.
Coal is our largest source of energy for producing electricity.
Mining and using coal produce many environmental impacts, including carbon dioxide emissions and acid rain.
Oil and natural gas are important sources of energy for many types of vehicles and uses in our homes and industry.
Nuclear energy is produced by splitting atoms. It also produces radioactive wastes that are very dangerous for many years.
Fossil fuels are nonrenewable sources of energy that produce environmental damage.

Review Questions

How does a fossil fuel form?
The hardest type of coal is called anthracite. Why is anthracite harder than other kinds of coal?
What product of nuclear energy has caused concerns about the use of this resource?
What is one important fuel that comes out of the oil refining process?
Which chemical element exposed in surface coal mining can cause environmental problems in nearby bodies of water?
Waxes can be made from the processing of which fossil fuel?
Why does natural gas need to be processed before we can use it as a fuel?
What are some problems with using coal?
What characteristic of gasoline is most important in making it a useful fuel for transportation? Explain.
Does nuclear energy cause air pollution? Explain.

Vocabulary

corrosive: Able to cause chemical changes to a substance that weaken or destroy the substance.
hydrocarbon: A chemical compound that contains only carbon and hydrogen.
metamorphic: A type of rock that forms when existing rock is exposed to high temperature and pressure.
nuclear energy: Energy that is released from the nucleus of an atom when it is changed into another atom.
sedimentary: A type of rock that forms from layers of sediment under high pressure.

Points to Consider

How are renewable sources of energy different from nonrenewable sources of energy?
Are all renewable energy sources equally practical?
Are all renewable energy sources equally good for the environment?

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