Spring 1999

[TEXT ARCHIVE WEB-PUBLISHED MARCH 2002.
ORIGINAL PRINT PUBLICATION DATE: SPRING 1999.]

Digging Dirt

Down and dirty activities courtesy of the cool folks at the Field Museum. If you like them, you'll find more in the "I Dig Dirt" activity kit available at the Field Museum.

Water Power

Goal: To demonstrate how water and temperature help form soil

You will need: A straw, Modeling clay, a glass of water, your freezer

Procedure: Place one end of the straw into the glass of water. Fill the straw by sucking water into it. Hold your tongue over one end to prevent water from escaping while you insert a clay plug into the open end of the straw. Plug the other end with clay. Lay the straw in the freezer for three hours. Remove the straw from the freezer and observe both ends.

What happened? You should have observed one or both of the clay plugs pushed out of the ends of the straw and a column of ice extending out of the end of the straw.

What did you learn? Water expands when it freezes. The clay plugs were pushed out of the ends of the straw because the water expanded when it froze. The same thing happens when water gets into cracks in rocks and freezes. The expansion of the freezing water is enough to push apart weak points in the rocks and can actually break the rock. This is one of the ways that rock is broken down to form the basis of soil. Rock also can be broken down through the growth of plants and fungi. When these start to grow in small crevices in the rocks, they force bits of rock to crumble off. Over time this broken-down rock becomes the soil in which other plants can grow.

Rock Eater

Goal: To demonstrate the effect of acids in soil formation

You will need: Two pieces of chalk, Vinegar water, two glasses

Procedure: Fill one glass halfway with vinegar, and the other glass halfway with water. Put a piece of chalk in each glass. Observe for a few minutes. Let the glasses sit overnight and observe again the next day.

What happened? During the first few minutes you may notice bubbles in the glass of vinegar. By the next day, the chalk in the vinegar has partially or totally disintegrated.

What did you learn? Chalk is made from limestone, a common rock in Chicago Wilderness. Vinegar is a weak acid. The chalk in the glass of vinegar disintegrates because the acid in the vinegar breaks the chemical bonds in the chalk. The bubbles you may have seen are carbon dioxide, a new substance formed when the limestone breaks down. Many natural processes produce greater or lesser amounts of acid. These acids are another way limestone rocks break down into the foundation for soil.

Critter Collecting

What is living in your soil? Many different kinds of tiny insects and other creatures live in the soil and the leaf litter just above it. You will be amazed at all you can find.

Goal: To discover the living things in your backyard

You will need: Notebook, ruler/thermometer, trowel, magnifier, field guide White paper plate or plain white paper

Procedure: Before you begin, use your notebook and thermometer to record today's date and temperature. Now go look for critters! Lift rocks, rotting wood, and piles of leaves. Do you see anything underneath? Use your trowel to dig down a few inches in the soil in a shady spot. Collect a sample of soil and place it on a white paper plate so that you can see the critters better. Use your magnifier to get a closer look at the critters. If you want to keep your critters longer, make a homemade bughouse. After observing your critters, return anything you find back to where it lives.

What happened? Record observations about your critters in the notebook. You can include both written descriptions and drawings. What types of critters did you find? Use a field guide to identify them. Where did you find them? Above the soil, in a pile of leaves or under a rock, or deeper within the soil? How many legs does each have, what color is it, how big is it? (Use your ruler to find out).

What did you learn? Soil makes a great place to live, especially if you're small. Food, water and hiding places are all around, and the climate is much more stable than it is above ground. An amazing array of plants, animals, fungi, and critters that are too small to see without a microscope live in the soil. You might try this activity several different times during the year. Do you notice a difference in the numbers and types of critters you find depending on when you look? Some critters live year-round in the soil, but burrow down deeper during the colder months. Other critters are "part-timers" living in the soil during some stages in their lives, but above ground as adults.