14. Regolith Formation

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.

Preperation

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.

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