Introduction to Activity

• Working in teams of 3 - 4, students are first asked to draw the earth and to sketch the thickness of the atmosphere, the depth of the ocean, and the height of the mountains. Next, they are asked to draw the same to scale.

Background

• This group activity has been used effectively with teachers in workshops (e.g., Gaia Crossroads Introductory Workshop). The objective is for participants to gain an appreciation of the length scales involved in global systems. This exercise often shows that people have a unrealistic view of the relative size of large-scale things.

Activity

• First, without knowing the actual dimensions of the earth, ocean depths, and atmospheric thickness, as each student to:
  1. Sketch out a circle representing a cross-section of the earth with sea level equal to 0.
  2. Draw Mount Everest (the highest continental mountain peak).
     • The highest peak on Earth is actually Mauna Kea on the island of Hawaii. This is because its total elevation should include not only its height above sea level, but also the distance it rises from the floor of the ocean
  3. Draw an ocean basin that shows relatively shallow shelves near continents, slopes dropping off to the ocean basins, and deep trenches.
  4. Draw the top of the atmosphere.
• Next, ask the students to repeat the exercise and make the drawing to scale.
  1. Earth is not actually round! It is a flattened (called "oblate") sphere whose radius at the poles is smaller (6,319 km) than at the equator (6,335 km).
     • For convenience, use a "medium" number for the Earth's radius: 6,325 km.
  2. Determine the heights of Mt. Everest, Mauna Kea, and the approximate depth of the East Pacific Basin (just east of Hawaii), using a world atlas for reference.
  3. With the same atlas, look up the depths of the ocean basins, continental shelves, and find out the depth of the Mariana Trench (western Pacific Ocean, west of the Philippine Islands).
  4. There is no "official" value of the thickness of Earth's atmosphere because it gets less and less (i.e., exponentially less) dense with altitude. A good "round number" to use for atmospheric thickness is 100 km.