What's Down There?

SEED

Activity Source: 

SEED (Shlumberger Excellence in Educational Development) with permission.

Throughout the Earth’s history, the cycle of erosion and deposition by water and wind has added layer upon layer of rock, soil, and organic material to the surface. Most sedimentary rock is beneath the surface.

To learn about sedimentary rock layers that we cannot see, geoscientists drill and bring up core samples of rock layers. Information from core samples, combined with that from other imaging techniques, allows geoscientists to map the depth and thickness of sedimentary rock layers below the surface. To learn more, see PlanetSEED (www.planetseed.com) and the full activity (www.planetseed.com/whats-down-there).

Materials

For each group of at least two or three students:

  • Transparent plastic box about 32 cm by 19 cm by 11 cm (12.5 in by 7.5 in by 4 in)
  • About 6 kg (13 lb) of dark sand and 3 kg (6.5 lb) of a lighter-colored sand, or about 3 kg each of three differently colored sands, in separate bowls
  • Two or three large paper or plastic cups
  • Two or three wooden rods or sticks
  • Non-toxic marker
  • At least 12 transparent plastic drinking straws
  • Graph paper
  • Ruler
  • Water
  • Paper towels
  • Several pages of blank paper or lightweight cardboard
  • Tape

Procedure

  1. With a marker, label the four sides of the box as “north,” “east,” “south,” and “west.”
  1. Add a few milliliters of water to each of the colored sands. Stir with wooden sticks to moisten all the sand.
  1. Place a 2- to 3-cm-thick (0.75- to 1.2-in) layer of moistened dark sand in the transparent box. Then work its surface so that it is uneven, slanting, wavy — anything but flat. Press down gently to remove all pockets of air. Do not let the other groups see what your group is doing.
  1. Still out of view of other groups, place a second and then a third uneven layer of moistened sand on the first, alternating sand colors. (If you have sands of three colors, you can place layers in any order.)
  1. Use paper or lightweight cardboard to make a tracing of each side of the box so that you clearly show the pattern of layers. You can also take photographs of each side. Do not show this information to the other groups.
  1. Cover the sides of the box with blank paper or cardboard, and tape, so that no one can see the pattern of the layers.
  1. Exchange boxes with another group.
  1. Now it’s up to your group to figure out the layer pattern of the box you received. Although this is only a model of layers of the Earth, what do you think a geologist would do? You can use any materials furnished for this, but do not remove the covering on the sides of the box.
  1. On a blank piece of paper, draw what you think the pattern of layers would look like for each of the four sides of the box.
  1. When everyone is finished, compare your drawings with the drawings or photographs created by the current owner of your group’s box. How accurate were you?
  1. Remove the covering on the sides of your box. How close are the layer patterns to your drawings or photographs?