The Scoop on Moon Dirt
Modified from "Regolith Formation," an activity in Exploring the Moon, A Teacher's Guide with Activities for Earth and Space Sciences, NASA Educational Product EG-1997-10-116 – HQ by J. Taylor and L. Martel.
Children ages 8 to 11 compare how soil forms on Earth and the Moon, exploring how water, wind, and impactors help to make soil.
What's the Point?
- Different soils form from different rock types and under different conditions.
- Earth's rocks break down (weather) through the action of water and wind.
- Lunar "soil" — regolith — forms when impactors strike the Moon's surface and pulverize the rock.
For the group:
- Poster paper
- Images of lunar footprints and the Moon
For each team of three to four children:
- 1 margarine container, filled three-fourths full with sand and water and frozen
- Access to a sink with flowing water (can be done with pitchers of water)
- 2 pieces of dry, brittle bread
- 1 (2"x2") piece of coarse sandpaper
- 1 large cardboard box (~2" per side) with high sides
- 10 –15 graham crackers (enough to cover the bottom of the box with two layers)
- Fist-sized rock or a (1–lb.) box of baking soda wrapped in aluminum foil
For the facilitator:
- Fill the margarine tubs about three-fourths full with sand; add water to completely cover the sand and freeze lightly.
A Word on Words . . .
The term "soil" is being used in this activity because children are familiar with "soil." "Regolith" is a more appropriate term and is introduced.
Soil: the unconsolidated (loose) top layer of material on Earth's surface that is made of minerals and, usually, organic matter in which plants grow.
Regolith: a general term for the layer of loose rock material that forms the surface of a planet — including Earth! — and covers the rock. Soil is a type of regolith. Other types of regolith include volcanic ash, materials deposited by a glacier or river, sand dunes, the red rocky surface materials of Mars, and the layer of material on the lunar surface.
Dirt: a term used by small children and gardeners to describe soil; a term used by scientists when they are unimpressed with the qualities of the regolith they are investigating or when they are more interested in the layers of rock beneath the regolith.
- Invite the children to tell you what they know about dirt or soil.
What is it made of? Where is it found? Are there different types of soils?
Share that the Moon and many planets and asteroids have a special type of soil on their surface, called regolith. Unlike the soil on Earth, the regolith on the Moon doesn’t have any organic materials: no seeds, roots, or bacteria.
Ask the children to share what they know about the Moon. Remind them that the Moon has no water and no atmosphere, in addition to other insights they may share.
- Invite the children to think about different ways regolith can form.
- What helps to break down rock on Earth? Flowing water, the expansion of freezing water, wind and wind-carried particles, plant roots widening cracks in rocks. The children may think of some of these ideas; the next part of the activity will give them firsthand experience with flowing water and wind.
- How might formation of regolith on the Moon be different from Earth?
- Place the children in groups. Provide each group with the frozen block of water and sand and ask them to imagine that this is a rock — a sandstone! Have the groups place their "rock" in the dishpan under the faucet and turn the water on at a slow to medium stream. Alternatively, use water poured from a pitcher or bottle.
- Bring the children back together to discuss what they found.
- What happens to the rock? The water wears it away.
- What does this tell us about how water contributes to the breakdown of rocks?
- Does this happen on Earth? You bet!
- Is there any flowing water on the Moon's surface? Nope.
- Does water help form regolith on the Moon? Nope.
- Now invite the children to explore how wind can break down rocks. Provide each group with a piece of dry, brittle bread and ask them to imagine it is a rock.
- What happens when their hand — acting like the wind — brushes across the bread? Small crumbs may fall from it.
- What happens when they rub a piece of sandpaper across the surface? Many more crumbs break away from the surface!
- Bring the children back together to discuss what they observed.
What does make regolith — the lunar "soil?" Do the children have any ideas? Show them the image of the Moon. What are the round shapes on the Moon's surface? How do they form?
- What process does this represent? Sometimes the wind is strong enough to carry particles of rock. These particles act like the sandpaper when they are blown against rock surfaces.
- What does this tell us about how wind contributes to the breakdown of rocks?
- Does this happen on Earth? You bet!
- Is there any wind blowing on the Moon's surface? Nope; the Moon has no atmosphere, so there is no wind.
- Does wind help form regolith on the Moon? Nope.
- Divide the children back into groups and provide each group with the container of graham crackers and large rock. The graham crackers are the lunar surface, the rock is a large asteroid! Ask the children to drop the asteroid, from about waist high, into the container.
- What happens?
- Have them repeat the process 5 times. What do they observe?
- Have them repeat the process ~20 more times. What do they observe?
- Bring the children back together to discuss their observations and thoughts.
- What process does this represent? Impactors striking the surface of the Moon — or Earth! — breaking down the surface rocks into regolith.
- What changed from one impact to five to twenty? The graham cracker rocks became more broken and the crumb regolith became thicker and finer.
- What does this tell us about how impacts by asteroids and comets contribute to the breakdown of rocks?
- Does this happen on Earth? Yes, but only rarely. Earth's surface is constantly "recycled" by wind and water and other processes, so the evidence of many of these craters has been erased. Earth's atmosphere also helps to protect us from being struck by smaller asteroids; they burn up in our atmosphere, making the beautiful streaks of light — meteors — that we occasionally see.
- Do impacts occur on the Moon? Yes, also rarely now, but wind and water do not flow on the Moon's surface. Once craters form, they are not altered by other processes unless they get hit by another rock from space! The Moon's surface preserves a record of almost four and a half billion years of impact, after impact, after impact, after impact!
- Do impacts help form regolith on the Moon? You bet! They are the main process forming lunar regolith.
Revisit with the children what they have learned.
- How do soils form on Earth?
- Do these same processes form regolith on the Moon?
- How does regolith form on the Moon?