Mapping the Ocean Floor

Objectives
Students will graph ocean depth data to create a profile of the ocean floor.
Students will infer the identity of ocean-floor features.

Materials
For each group of students in the Engage/Explore activity:

For each student in the The Shape of the Ocean Floor activity: Procedures
I.   Activating Prior Knowledge
Ask students:  What does the ocean floor look like?  Encourage students to share what they have seen in books, on television, and in movies.  Lead students to the understanding that the ocean floor has a varied surface, not too different from the land's surface.

II.    Engage/Explore
Advance Preparation:  Obtain as many small cardboard boxes with lids as there will be groups of students doing the activity.  In the bottom of each box, glue or tape an object whose identity could be inferred by determining its contours, such as a ball, small toy, spool, or spoon.  Use a different object in each box, making sure each object clears the lid by at least 2 cm.  With a sharp pencil or awl, poke 10-15 holes in the lid at various location.

Student Procedures:

  1. Your teacher will provide your group with ten plastic drinking straws and a covered box containing a mystery object.  The top of the box has several holes punched in it.  Using the straws as probes, try to determine the size, shape and location of the object inside the box.
  2. Based on the information you gathered, describe your object.  What can you say about its length, shape, and position?  Write down your hypothesis about the identity of the object.
  3. Remove the box top to reveal the object.
Expected Outcome:  Students may not be able to determine the object's identity with certainty, but they should be able to suggest reasonable possibilities.

Discussion:  Discuss with students how this method of indirect observation is similar to the use of sonar to map the ocean floor.

III.    Activity:  The Shape of the Ocean Floor
Imagine you are an oceanographer traveling across the Atlantic along the 45º N latitude line.  You and your crew are using sonar to gather data on the depth of the ocean between Nova Scotia, Canada, and the town of Soulac on the coast of France.  In this activity, you will plot depth data to create a profile of the ocean floor.

Student Procedures:

  1. Draw the axes of a graph.  Label the horizontal axis Longitude.  Mark from 65º W to 0º from left to right.  Label the vertical axis Ocean Depth.  Mark 0 meters at the top of the vertical axis to represent sea level.  Mark -5000 meters at the bottom to represent the depth of 5000 meters below sea level.  Mark depths at equal intervals along the vertical axis.
  2. Examine the data in the table.  The numbers in the Longitude column give the ship's location at 19 points in the Atlantic Ocean.  Location 1 is Nova Scotia, and Location 19 is Soulac.  The numbers in the Ocean Depth column give the depth measurements recorded at each location.  Plot each measurement on your graph.  Remember that the depths are represented on your graph as numbers below 0, or sea level.
  3. Connect the points you have plotted with a line to create a profile of the ocean floor.
Ocean Depth Sonar Data
Longitude (º W)
Ocean Depth (m)
1.  64 0
2.  60 91
3.   55 132
4.   50 73
5.   48 3512
6.   45 4024
7.   40 3805
8.   35 4171
9.   33 3439
10. 30 3073
11. 28 1756
12. 27 2195
13. 25 3146
14. 20 4244
15. 15 4610
16. 10 4976
17. 05 4317
18. 04 146
19. 01 0

Analyze and Conclude

  1. On your graph, identify and label the continental shelf and continental slope.
  2. Label the abyssal plain on your graph.  How would you expect the ocean floor to look there?
  3. Label the mid-ocean ridge on your graph.  Describe the process that is occurring there?
  4. What might the feature at 10º W be?  Explain.
Teacher Tip:  The graph works best if students tape two 8 1/2 x 11-inch pieces of graph paper together along the 8 1/2-inch side so they can spread out the horizontal axis.

Answers to Analyze and Conclude

  1. Continental shelf:  locations 1-4 and 18-19; continental slope:  Locations 4-5 and 17-18
  2. Abyssal plain:  Locations 5-9.  The ocean floor would look smooth and nearly flat except for seamounts.
  3. Mid-ocean ridge:  Locations 9-13.  Seafloor spreading is occurring.  Magma rises up between the two plates, hardens, and adds new rock to the ocean floor.
  4. The bottom of a trench; trenches are the deepest parts of the ocean floor.

Reference:  Laboratory activity (part III of lesson plan) was taken from page 155 of Simons, Barbara Brooks, and Thomas R. Wellnitz.  Science Explorer:  Earth's Waters. Upper Saddle River: Prentice Hall, 2000.