Experiment

This activity created in partnership with AGI.

Think about the energy you use every day to cook, heat or cool or light your home, or to travel from one place to another. For most of us, the main sources of this energy are the fossil fuels: coal, oil, and natural gas. Whether used directly, as gasoline, heating oil, or natural gas, or to generate electricity (by burning coal), fossil fuels are a large part of the world’s energy picture. But how do fossil fuels form?

Illustration courtesy of Carolyn Finley. Oil and natural gas deposits are trapped between layers of porous and nonporous rock.

The story starts millions of years ago, during the Carboniferous Period of the Paleozoic Era. The Earth was warm and was covered with plant-filled swamps and shallow seas teeming with algae and simple animal life forms such as plankton. When the plants and animals died, their remains fell to the bottom of the swamps and seas and accumulated there. Much of the organic matter decayed before it was buried by more sediment. Some of it, however, was buried before it could decay. Over millions of years, more and more sediments accumulated and the great heat and pressure changed the plant and animal materials into coal, oil, and natural gas. These deposits can be trapped between layers of porous and nonporous rock, as seen in the diagram.

Watch the video to learn how petroleum is formed underground. Natural gas is found in nearly all petroleum deposits. Coal forms in a similar manner. All three types of fossil fuel are nonrenewable resources because they are used more quickly than they can be replaced.

Our Experiment

In this activity, you will make a model of how natural gas might be formed from decaying organic material. Although the conditions of the activity are very different from those that produce natural gas, this will give you an idea of how the process works.

Tools and materials

• Two 1-L (1-qt) plastic bags (reclosable or nonreclosable)
• Leafy green vegetables, such as lettuce, cabbage, or spinach, at room temperature
• Large clear measuring cup
• Measuring tape
• Notebook
• Pen or marker
• Tape for sealing the bags (if needed)
• Thermometer
• Camera (optional)

What to do

Take out your leafy green vegetables and let them come to room temperature. Tear them into pieces no larger than your hand.
Add the greens to the measuring cup and pack them down as much as possible. Keep adding greens and pushing them down until the level of the greens is at the 250-mL (8-oz, or 1-c) mark.
Fill one of the plastic bags with the greens from the measuring cup and mark it as bag 1. Repeat the process for the second bag and label it bag 2. You should have two bags that each contains 1 cupful of greens.
Distribute the greens evenly along the bottom of each bag. Then roll up each bag from the bottom—to press all of the air out—and seal tightly. If the bag is not reclosable, use tape to seal the bag. This removes most of the oxygen and sets the stage for something similar to anaerobic decay, or decay in the absence of oxygen.
Use the measuring tape to find the circumference of the two rolled-up bags. Record this information in your notebook. Write a description of your greens—how they look and feel—or take a photograph of each rolled-up bag. Then record the temperature of the room.
Unroll the bags and place them on a table or shelf where they can remain at room temperature. Be sure the bags are not in sunlight, because this will heat the air inside the bags, causing them to expand and give a false reading.   Make a table in your notebook to record your observations. Here is one example of how to set up the table.     Day 1 date Day 2 date Day 3 date Day 4 date Day 5 date Day 6 date Day 7 date Day 8 date Day 9 date Day 10 date   Temperature (°C)                     Bag 1 Measurement (cm)                     Observations                     Bag 2 Measurement (cm)                     Observations                     Once a day for the next ten days, gently roll each bag and measure the circumference. Measure the room temperature, which should stay about the same. Record this information in your notebook.   After making your measurements, look at the greens and write down your observations of their appearance. You might also find it useful to take a picture of the bags each day.   On the tenth day of the experiment, measure a final distance around each of the rolled bags. Record these two final measurements and the room temperature in your notebook. How have these measurements changed over the ten days?   After you have made your final measurements, discard both bags.   What changes did you see in the bags? How can you explain what you see? How do these changes relate to what you know about how decaying material produces natural gas? Write your thoughts in your notebook.

	Digging Deeper Find out more about What is Natural Gas?