Decomposition

Decomposition is the natural pprocess of decay. Often the decompositon of materials surrounding a body can give a forensic scientist valuable information. Not all materials decompose at the same rate. Organic material, which is material from plants or animals, decomposes differently from inorganic, or man-made, material. Forensic scientists can study the state of decomposition of these materials to approximate time of death. Try this activity to learn materials can decompose at different rates and how that information can help solve crimes.

Materials

- clear plastic 2-qurt (2-liter) soda bottle
- scissors
- cheesecloth
- rubber band
- tape
- 2 cup (500 ml) sand
- 2 quarts (2 liters) garden soil (from an outdoor location)
- organic material, such as leaves, twigs, grass, shredded newspaper, and needles
- inorganic materials, such as Styrofoam, plastic, and scraps of fabric or leather
- pen or pencil
- notebook
- rubber gloves
- several sheets of newspaper
- stick
- worms (optional)
- tap water
- adult helper

Procedure

NOTE: This activity requires adult help.

1. Remove the label as best you can from the plastic soda bottle.
2. Have your adult helper cut the bottle into two sections, making the cut approximately one-third of the way from the bottom.
3. Cover the mouth of the bottle with cheesecloth and secure it with the rubber band.
4. Turn the drop section of thebottle upside down and place it in the bottom section as shown. Tape the two sections together.
5. Put the sand in the upside-down container. Place a 1-cup (250 ml) layer of the garden soil on top of the sand.
6. Look at the organic and inorganic materials. Which items do you think will decompose quickly? Why? Whicj items do you think will take longer to decompose? Why? Record your predictions in your notebook.
7. Add a small amount of each organic and inorganic materialto the container, then add another layer of soil. Continue to layer organic and inorganic materials and soil until they reach the top of the container. Add more materials on top of the last layer of soil.
8. Add worms to the container, if you like.
9. Pour water into the container until it starts to drip through the cheesecloth.
10. Set the container where it will not be disturbed for a month. Water the container twice a week.
11. Observe the container every other day. Record your observations.
12. After a month, put on the rubber gloves and pour the contents of the container onto the newspaper. Use the stuck to move the soil arround. Observe the condition of the organic and inorganic materials. Were your prediction correct?

CAUTION: Always wear rubber gloves when examining the experiment materials. Return worms to the earth and throw out the rest of the project when you are finished. Be sure to wash your hands thoroughly when you are done.

Explanation

Decomposition is nature’s way to recycle organic, or living, material. Organic material is broken down into nutrients that can be reused by plants as they grow. Some inorganic, or nonliving, material is broken down as well, but usually at a slower rate. Bacteria, fungi, worms, and microorganisms all help to break down these materials.

Worm in particular help to speed up the process of decomposition. They make extensive networks of tunnels that help air and water reach the roots of plants. The tunnels also provide air and water for other soil-dwelling insects and small organisms that help with the process of decomposition. Worms also turn the soil by moving deep soil up to the surface and by dragging plant materials underground. One cup (250 ml) of soil may contain more than 5 billion living creatures!

Forensic scientists use their knowledge of the decomposition rates of various substances to help solve crimes in several ways. For example, the state of decomposition of a letter found behind a house could link a suspect to the time of robbery, while a rotting apple core could be an important clue for police looking for a lost camper.