Model the ocean floor in a shoe box and take depth measurements

1. Discuss how oceanographers use remote sensing to learn about the ocean.

Satellites are useful in tracking sea surface temperatures and currents, but they cannot penetrate below the ocean surface. New technology does allow satellites to infer the depth of the ocean.

Sonar uses sound waves reflecting back from objects to track schools of fish, locate submerged submarines, and map the ocean floor.

1. Demonstrate how sonar works by placing a glass pie plate filled with water onto an overhead projector so that the image of the water projects onto a screen.
2. Let one drop of water from an eyedropper fall into the middle of the pie plate from a height of 6-12 inches above the plate. This will create a wave that radiates outward from the middle of the plate and bounces back from the sides, simulating how sonar reflects sound waves back from objects.
3. Explain that until the invention of sonar during World War II, oceanographers mapped the depths of the ocean by dropping a weighted plumb line over the side of a ship and measuring the length of rope that was let out. These measurements of the ocean's depth were called soundings. This technique was comparable to someone trying to map the continental United States by lowering a rope every 50 miles or so from an airplane as it flew over the country.
4. Show students a topographic chart of the sea floor. Ask them to pick out geologic features like sea mounts, valleys, plains, etc. Compare charts of the Gulf of Maine and of the Caribbean Sea for depth.

Measure their relative distance from the equator

1. Have the students create their own model of the ocean floor by layering spackling compound in the bottom of their shoe box. Their model should be simple, yet include some ocean features like valleys and hills. These will take at least 24 hours to dry.
2. Have them tape graph paper to the top of the shoe box lid.
3. Using a narrow awl, punch a series of small holes in several gridline intersections.
4. With a black felt-tip marker, make 1cm. markings on the straws. Each centimeter represents one mile of ocean depth.
5. Number the grid from left to right (i.e. 1-10). Then assign a letter to each grid from top to bottom (i.e., A-M).
6. Do this on the graph paper on the shoe box lid as well as on the second sheet of graph paper on which the student will record their soundings.
7. Exchange shoe boxes with another team.
8. Using the graduated straw as a plumb line, measure the depth of each hole in the shoe box lid. Students start at the far left and top and work their way across the graph paper. One person makes the sounding and reads off the depth of each hole, while another records it on graph paper. Record the depth of each hole on the graph paper.
9. When students have completed taking all the soundings, have them draw lines to connect all similar depths.
10. Then have the students use different color markers for each depth.
11. Ask them to name the ocean features they have mapped, such as hills, valleys, plains, etc.
12. Have them remove the shoe box lid to see if they made an accurate chart of the sea floor.
13. Using spackling compound or modeling clay, have one group of 4-5 students try to recreate the bottom topography of the Gulf of Maine on a 2-foot square piece of plywood. When the surface dries, have them paint land and water areas to improve the definition of land and sea features.
14. Another group recreates the topography of the Caribbean Sea on poster board.
15. Have two other groups of students draw topographic charts of each region.

Materials

• Two glass pie plates filled with water