Hawai'i Space Grant Consortium, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, 1996

Regolith Formation
Teacher Page
Purpose

To compare the process of regolith formation on Earth and on the Moon.

Background

The loose, fragmental material on the Moon's surface is called regolith. This regolith, a product of meteoritic bombardment, is the debris thrown out of the impact craters. The composition and texture of the lunar regolith varies from place to place depending on the rock types impacted.

Generally, the older the surface, the thicker the regolith. Regolith on young maria may be only 2 meters thick; whereas, it is perhaps 20 meters thick in the older lunar highlands.

By contrast, regolith on Earth is a product of weathering. Weathering encompasses all the processes that cause rocks to fragment, crack, crumble, or decay. These processes can be physical (such as freezing water causing rocks to crack), chemical (such as decaying of minerals in water or acids), and biological (such as plant roots widening cracks in rocks).

The rock debris caused by weathering can then be loosened and carried away by erosional agents -- running water (fast-flowing rivers, rain, ocean waves), high-speed wind (by itself or sandblasting), and ice (glaciers).

In this activity, procedures A and B challenge the students to determine the effects of wind, sandblasting, and water on regolith formation and deposition on Earth. This is followed by prodedure C in which the students simulate regolith formation on the Moon by meteoritic bombardment.

Preparation

Review and prepare materials listed on the student sheet.

Toast, crackers, or brittle cookies can be used in this activity. Toast is the least expensive but most time consuming choice. In any case, students will need two different colors of materials for procedure C; for example, vanilla and chocolate graham crackers. Invariably, students get hungry at the sight of food, so you may want to reserve some clean materials for consumption or use something other than a rock for the projectile.

To prepare bread: use a conventional oven, toaster, or sun-dry method to produce the most crisp and brittle toast. Toast one loaf of white bread and one loaf of golden wheat or rye bread. Note that whole wheat bread does not get brittle enough.

For procedure B, fill margarine containers (one for each group) with water and sand, then freeze. The more sand, the better the illusion to a real rock.

For procedure C, do not use glass pans. Large plastic tubs are preferred for this procedure, but recyclable aluminum roasting pans or shallow cardboard boxes work as well.

In Class

Divide the students into cooperative groups and distribute materials.

Discuss the definition of regolith. Have students guess how regolith is formed on Earth and on the Moon. Ask students for justification.

If sand paper or nail files are not available, then students can use the edge of a ruler to illustrate the effects of sandblasting in procedure A. Caution students to use a collection tray in the sink in procedure B to avoid sand-clogged drains. An alternative to using a faucet is to have the students pour a steady stream of water from beakers onto their ice-cube rocks to illustrate the effects of falling water.

Have students guess individually, then discuss in groups, what the surface of the Moon is like (hard rocks, fine dust, large boulders). Ask students for justification of their answers.

Refer to a photograph of an astronaut's bootprint on the surface of the Moon. Givestudents the opportunity to change or confirm their guesses.

Procedure C is best done outside. Drop the rock from waist high. Sometimes the impacting rock causes the pan to bounce so you may want to secure the pan to the ground with tape. Students should stand back as a safety precaution.

Wrap-up

After participating in the activity, have the whole class compare and contrast regolith formation and ask each small group to verify their original guesses.


Go to Regolith Formation Student Pages.
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http://www.spacegrant.hawaii.edu/class_acts/