The Unseen Ocean Floor

Introduction: This lesson works well as part of an introduction to bathymetry and sea floor features, and also introduces one of the most widely usd methods for studying the ocean.

What to Expect: This exercise may be done dry, using an opaque box with a cover, or wet, using colored water to hide the ocean floor features. If you choose to use water, be prepared for splashes and spills.

Materials:

• Dishpan, box, or plastic container the size of shoebox or larger
• Clay or waterproof modeling compound
• Straw, wooden skewer, plastic pipette, or pencil long enough to measure depths
• Graph paper
• Fine point permanent marker
• Food coloring
• Colored pencils
• Centimeter ruler

[NOTE: If students are designing their own methods for measuring depth, provide a wide variety of materials such as string, small weights, push pins, cardboard, grid templates, and so on.]

Procedure:

1. Introduce different types of ocean floor structures, including continental shelf, continental slope, abyssal plain, seamount, island, rift zone, mid-ocean ridge, and oceanic trench.

2. Have teams of students use clay or modeling compound to create models of the ocean floor in the containers, including some of the features introduced above. For younger students, two orthree prominent features are appropriate; for older students, leave the possibilities open. Sea floor features will be covered with water; any feature above about two-thirds of the container’s depth will be appear as an island or continent.

3. Each team should mark the top of its box at regular intervals, using numbers along one side and letters along the other: ten markings along the long side and five along the shorter side will be appropriate for most containers. The markings will form a grid system of reference points, such as B5 or E3, for students to use when deciding where to sample. If using water-filled containers, students can make a grid using string stretched across the top of the container.

4. Each box should be covered with a grid-marked top. If using water, have each team of students fill its ocean basin about two thirds full with water colored with food coloring to make it opaque. Students may choose a blue ocean or be creative!

5. Have students use the centimeter ruler and marker to mark their measuring instrument (pencil, straw, etc.) in centimeter increments.

6. Each team of students should exchange models with another team. Students should:

• Decide on a method and strategy for sampling, then carry it out, using graph paper to record their depth measurements.
• Create a map showing topography of the ocean floor that they have been given.
• Using clay or another material of their choice, construct a 3-D model of their unseen ocean floor based on the measurements they made.

7. Have students drain the oceans and compare the original ocean floors with the duplicate models. This can be made into a dramatic moment of unveiling, with as much fanfare as you wish to create.

Evaluation: Students should describe their sampling plan orally or in writing; students should be able to name the features on the sea floor models; students will hand in their depth recording data; and students should self-evaluate the accuracy of their duplicate models and explain discrepancies.

Extensions:

1. Have the students map another unknown ocean floor box, but this time give the students a funding constraint that only allows a certain number of sampling stations. Have student groups decide where to sample. How does the limitation affect the accuracy of their results?

2. Introduce nautical charts and topographic maps

3. Older students can bring their models to elementary students and lead the younger children through a sampling demonstration