Poverty Point Ovens:

Getting the Temperature Right!

Subject Areas:
Language Arts, Science, Social Studies, Math

Objectives:
The student will:

Time:
One hour to make cooking balls (60 gram PPOs from Poverty Point Cooking Balls activity may be used)
One hour to set up earth ovens in pots
Two one-hour class periods for experiment and conclusions

Materials:
Loess soil and water or 60 gram cooking balls made during Poverty Point Cooking Balls activity
Soil to fill terra cotta pots
4 inch diameter terra cotta pot for each student group
Measuring cups
Heat safe thermometers
Tongs for picking up hot cooking balls
Thin colored markers
Poverty Point Cooking Balls overhead transparency
Digital watch or watch with minute hand
Scales
Tape
Ruler
Oven or toaster oven

Must Know Info:

Earth oven cooking was an innovation created by the Poverty Point people. They made cooking balls by mixing the local soil with water and forming the mud into various shapes. These cooking balls were placed in the bottom of earth oven pits and heated with fire. Food items were probably wrapped in leaves or other material before being surrounded by the hot cooking balls. The earth oven and food were then covered by soil, sealing the oven shut. This cooking method is particular to the Poverty Point Culture.

Experiments have shown that the temperature inside an earth oven is influenced by the number and kind of cooking balls which are used. Experimenters could control how hot the oven got and how long the oven stayed hot by the cooking balls they used. Because of this, archaeologists hypothesize that the cooking balls may have been used as a type of thermostat by Poverty Point people.

The most frequently found cooking ball shapes are identified in the Poverty Point Cooking Ball activity. Cooking balls made during that activity may be used to complete this experiment if the mud for each wet cooking ball weighed 60 grams. Archaeologists note that most Poverty Point cooking balls weigh between 50 and 60 grams. Weigh the dried cooking balls and find samples of different kinds which have the same weight. This will insure that the cooking balls have the same amount of material or mass. Because they have different shapes, each cooking ball will have a different amount of surface area. Students will be testing the hypothesis that the differing amounts of surface area account for the differences in heat retention. Line graphs of student data will show the rate at which different cooking balls release their heat energy. It is helpful to graph each cooking ball type in a different color for clarity. There is no "correct answer" for this activity. Students are using the scientific process just like archaeologists.

Divide your class into groups of three students each. Each group will work together to build one earth oven terra cotta pot and test one kind of cooking ball. Group members will work as a timer, a recorder, and a thermometer reader during data collection. Because this activity involves very HOT cooking balls, you will want to supervise students closely! It may be advisable to work with a limited number of groups at one time when adding the hot cooking balls to the earth oven pots.

Procedures:

1. Show students the transparency of Poverty Point cooking balls from Poverty Point Cooking Balls activity. Brainstorm ideas about why so many different shapes were made. Tell students that some archaeologists wonder if the Poverty Point people used the different shapes as thermostats in the same way that we use our microwave oven power levels. Each group should pick a different shape to test.

2. Go over Poverty Point Ovens: Getting the Temperature Right! handout with students prior to beginning the experiment. If you are using cooking balls constructed during the Poverty Point Cooking Balls activity, it is important that you find cooking balls of different shapes which have the same weight for this experiment. If you make the balls as a part of this activity, measure the mud mixture so that each ball has a "wet" weight of 60 grams. Weigh the balls again after they dry and compare the differences. Use different shapes of cooking balls with identical weights for this activity.

3. Proceed with steps in the handout to make the cooking balls and to set up the terra cotta pot earth ovens.

4. Heat the cooking balls in an oven or toaster oven on high for 30 minutes prior to continuing the experiment. An adult must pick up the cooking balls with tongs and place each one in a different group's earth oven. They will be very hot! You may want to heat several cooking balls at once in order to start several groups at the same time.

5. Students will immediately cover the hot cooking ball with dirt and record a beginning temperature for the earth oven. Students should read and record temperature data every minute after the cooking ball has been put into the oven for 30 minutes or as long as possible.

6. After each group has conducted the experiment, give groups an opportunity to share their data with the rest of the class. Each group will make a line graph showing their cooking ball data. Make a whole class line graph showing the results for all of the earth ovens. Students will draw conclusions from this graph about which cooking balls release heat very quickly or retain it over time.

7. Students will reach conclusions about which kind of cooking ball they would want to use to get a beginning high temperature in an earth oven or which kind of ball they might use to keep the oven hot over a longer period of time. Perceptive students will start hypothesizing about combinations of different kinds of cooking balls.