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Activity: How Much Water?

NGSS Science and Engineering Practices:

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:

Using two maps of the world, determine approximately how much of the surface of the earth is land and how much is covered by water. 

Materials

  • Figs. 1.8.1 and 1.8.2
  • Tables 1.1–1.6
  • Globe
  • Pencil or pen
  • Colored pencils or crayons (optional)
  • Calculator (optional)

Procedure

  1. Compare the equal-area and cylindrical-projection maps (shown in Figs. 1.8.1 and 1.8.2) to a globe. Hypothesize which type of map you think is a better representation of the surface area of the ocean basins and continents. Write down your hypothesis, and make sure to include your reasoning.

<p><strong>Fig. 1.8.1.</strong> Equal-area map with superimposed grid. One square at the equator represents a surface area of about 1,240,000 square kilometers. On this map land is grey even if it is covered by ice. This map does not show sea ice.</p><br />
<p><strong>Fig. 1.8.2.</strong> Cylindrical-projection map with superimposed grid. One square at the equator represents a surface area of about 1,240,000 square kilometers. On this map land is grey even if it is covered by ice. This map does not show sea ice.</p><br />


  1. Using Tables 1.1 and 1.2, mark and label the boundaries of ocean basins and continents on both maps (Figs. 1.8.1 and 1.8.2). For this activity, group the islands with the continent closest to them. You may use colored pencils or crayons to color-code the maps. Make a map legend that explains how the boundaries are labeled and how your coloring of the boundaries shows information.
     
  2. Determine the surface area of the ocean basins and continents for each map by counting and recording the number of squares.
    1. If you are completing this activity in a group and splitting up tasks, make sure everyone is consistent in their methods. Be prepared to give reasons for your decisions. For instance, determine how the group will count squares that are partially land and partially ocean.
    2. Count the squares for the surface areas of each ocean basin and each continent on each map. Record this information in Tables 1.3 and 1.4.
       
  3. Collect and record the square count for the surface areas of the continents and ocean basins from each group in the class. Calculate class averages. Record this information in Tables 1.3 and 1.4.
    1. Using the class average data, calculate the apparent area by multiplying the number of squares counted by the surface area of each square. 
    2. Record this data in Tables 1.3 and 1.4. Use the class average data for the rest of the procedure.
       
  4. Rank the continents and ocean basins in order of size. Rank the largest as number 1, the next as number 2, etc. Record your data in Tables 1.3 and 1.4.
     
  5. Fill in Table 1.3 and 1.4 with the accepted values for each continent and ocean basin given to you by your teacher.
     
    1. Rank the continents and ocean basins using the accepted value areas. 
    2. Record your data in Tables 1.3 and 1.4. 
  6. Calculate the percentages of the surface area of the earth covered by the continents and by ocean water.
    1. Add up your calculated area for the continents and ocean basins in each map from Tables 1.3 and 1.4. Record this data under the columns “Total area equal-area” and “Total area cylindrical” in Table 1.5. 
    2. Add the surface area of continents and the ocean for each map to get the total surface area of earth. Record this number in Table 1.5.
    3. Calculate the percentages of the surface area of the earth covered by continents and by ocean water using the formula


    4. Using the scientifically accepted surface areas for the continents and ocean in Table 1.5, calculate the scientifically accepted percentage of each.
       
  7. Calculate the approximate volume of each ocean basin in Table 1.6. Use the values you calculated from Table 1.4, the given average depth of each ocean basin in Table 1.6, and the formula below to calculate the volume:

    Volume = Area x Depth
    1. Rank the volume of the ocean basins by size for both both equal-area and cylindrical projection maps in Table 1.6.
    2. Rank the largest ocean basin as number 1, the next largest as number 2, etc.
       
  8. Fill in Table 1.6 with the scientifically accepted values for each ocean basin volume (given to you by your teacher). Rank the largest ocean basin as number 1, the next largest as number 2, etc. Record your data in Table 1.6.
Activity Questions: 
  1. Compare the rank order of the apparent surface area for ocean basins and continents in Tables 1.3 and 1.4.
    1. Is the rank order the same for an equal-area map as it is for a cylindrical-projection map? If not, explain why it is different.
    2. How does the rank order of each map compare with the rank order of the accepted values?
       
  2. Compare the percentage surface area for the continents and the ocean in Table 1.5.
    1. How do the percentages of land and ocean on a equal-area map compare to those on a cylindrical-projection map? 
    2. How do the percentages from each map compare to the accepted value percentages?
       
  3. Compare the rank order of the volumes for the continents and the ocean basins in Table 1.6.
    1. Is the rank order the same for an equal-area map as it is for a cylindrical-projection map? If not, explain why it is different.
    2. How does the rank order from each map compare with the rank order of the accepted values?
       
  4. List the ocean basins from largest to smallest. Which ocean basin is the largest? Which is the smallest? (Consider each ocean basin's area, depth, and volume.) Include the reasoning for your decision.
     
  5. Compare equal-area maps, cylindrical-projection maps, and globes.
    1. Compared to a globe, which map gives the more accurate measure of surface area?
    2. Which map distorts the continents and ocean basin shapes least?
    3. Which map shows distances more accurately?
    4. Which map shows directions more accurately?
    5. Which map is easier to read? Why?
    6. When would you use each type of map? Why?
    7. What are some other advantages and disadvantages of equal-area and cylindrical projection maps?
       
  6. Did you find that different groups had different counts for their number of squares of land and water? If so, why do you think they were different? Why do you think you were asked to calculate the class averages of your counted squares? If you had not used the class averages for the rest of the procedures, how would your results have been affected?
     
  7. When you compared your estimates of surface area and volume to results accepted by the scientific community, what did you find? Were your class’s estimates of land and water surface area different from those of the scientific community? If so, why do you think they were different?
     
  8. In textbooks and popular literature it is commonly reported that the world ocean covers over two-thirds of the earth. How does this estimation compare to the percentages calculated in Table 1.5?
     
  9. Explain the difference in meaning between each of the following terms:
    1. apparent surface area and accepted surface area
    2. surface area, volume, and depth

Table of Contents:

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.