To Rot or Not to Rot

Educator's Guide: Activity

Time required: This activity will cover a month of observation for at least fifteen minutes once a week. Plan one period for an introduction and one for a conclusion.

Age level: grades 5 - 10

This activity demonstrates the scientific method and shows students firsthand the effect of environment on the preservation of organic materials. Some archaeological sites are in hot, dry deserts; some in frozen tundra; some under water; some in caves; some in soils that drain well, or in wet clays. In damp conditions, bacteria that decompose vegetable matter may be sealed off from oxygen. Artifacts buried in wet environments are "preserved" until exposed to air. If not properly treated, they immediately begin to decompose. Students learn that some evidence from past cultures survives over time and some does not. The activity simulates what happens to materials on an archaeological site - but don't share this with your students until the four-week observation period is over.


  • 30 clear plastic cups (8-ounce)
  • 30 pieces of fruit, such as apples, berries, plums, grapes, etc.
  • water
  • plastic wrap
  • a freezer
  • a refrigerator
  • pottery clay (enough to wrap six pieces of fruit)
  • heat lamp
  • masking tape
  • pea-sized gravel (7 1/2 cups)
  • rubber bands
  • worksheet: Observation Worksheet download pdf (53K)

Establish workstations that simulate a specific "site condition": cool and warm places in the room, in the refrigerator, and under the heat lamp. 
Divide the class into five groups. 
Give each student an observation worksheet.
Give each group five cups. Have the students in each group set up the cups and label them with masking tape as outlined below: 

Cup 1 (Condition 1 - Frozen) Label the cup "frozen." Put the fruit in the cup, surrounded by gravel, but so the fruit can be seen through the cup. Fill the cup with water and place the cup in a freezer.

Cup 2 (Condition 2 - Dry) Label the cup "dry." Fill the bottom of the cup with 4 cm of gravel and carefully place the fruit on it or into the gravel, but so that it can be seen easily. Place in a hot, dry location (under lamp).

Cup 3 (Condition 3 - Humid) Label the cup "humid." Fill the bottom of the cup with 4 cm of gravel and place the fruit carefully on top of it. Add water until it just touches the fruit. Seal the cup with plastic wrap and rubber bands. Be sure the fruit can be seen from the outside. Place the cup in a room temperature location.

Cup 4 (Condition 4 - Under water) Label the cup "under water." Same as Cup 1, but stored in a refrigerator or cool place (not a freezer).

Cup 5 (Condition 5 - Wet clay) Label the cup "wet clay." Compress damp clay around the fruit and wrap with plastic wrap. The fruit must be as airtight as possible. Fill the bottom of the cup with 3 cm of gravel and fill the cup with water until it just begins to show on top of the gravel. Place the clay ball on top of the gravel and seal the cup with plastic wrap and rubber bands. Store in a refrigerator or cool place (not a freezer).

Have students put their cups in the appropriate places around the room. Some of these components or factors are called variables; others are called constants. Have the students brainstorm which are which. Factors that differ at each site are variables: temperature, humidity, and the material that surrounded the fruit: air, water, clay. Factors that stay the same at each site are constants: cup, fruit, and gravel.

Ask students to hypothesize about what will happen to each of their fruits. Tell them that they will observe any changes over the next four weeks. Remind them that they cannot open their clay cups until the end of the experiment.

The Experiment

Each group will observe its fruit every seven days and will note changes in size, shape, color, and any other characteristics on their worksheets. (Students should receive a separate worksheet for each week of the four weeks of observation). At the end of the fourth week students should write up their conclusions and present them to the class. Ask students to compare their results with their original hypotheses. Have students brainstorm natural analogs (environments on Earth) to each of the 5 conditions. Discuss how the different variables affected preservation, and which conditions resulted in the best preservation.

Most likely outcomes:

1. Frozen (e.g., Arctic site) Fruit remains the same
2. Dry (e.g., desert cave site with extremely little moisture) Fruit shrivels up
3. Humid (e.g., anyplace with a lot of moisture) Fruit rots (smells are terrible)
4. Underwater site Fruit rots
5. Wet clay (e.g., a site that has been covered with mud and always remained wet) Fruit remains almost nearly unchanged

This activity is adapted from