Science - 4th Grade
Standard 3 Objective 3
1 class periods of 60 minutes each
Soil is composed of living, nonliving, and once living components. Students discover these materials as they get their hands dirty in a bucket of soil. Students then study the differences between humus, sand, and clay. They will observe these samples dry, wet, and in settling tubes. This is a great introduction lesson and covers Object 3 A and B extremely well.
Soil is the top layer of most of our earth. Soil is partly made up of decaying plant or animal remains. These are called organic matter or humus and contain the living and once living components of our soil. Soil mostly contains pieces of disintegrating rocks or inorganic matter, water, and air. The differing amounts of inorganic and organic material in a soil sample provide for the different types of soil that we have.
Soil is home to many plants and animals, it provides nutrients and support for plants and crops, helps filter and store water, decomposes waste, and provides natural resources that we depend on.
Soil is usually layered. The uppermost layer is called topsoil and this layer contains humus, plant roots, and living creatures. The more humus found in topsoil, the more nutrient rich the topsoil and the better the conditions for growing plants. The middle layer is called subsoil. This contains more clay and less organic matter. Beneath this is a layer of rocks called bedrock. As the bedrock or parent material is broken down it becomes weathered into bits and pieces naturally by water, ice, wind, and plants. These bits and pieces of rock form a large part of our soil.
Weathered rock comes in a wide range of shapes and sizes. The largest particles in soil are gravel (larger than 2 mm). The other particles in soil are sand (less than 2 mm), silt (less than 1/16 mm), and clay (less than 1/256 mm). The smaller the particle size the more easily water is held in the soil. The larger particle size the easier it is for water to seep through it and this soil contains lots of air. Roots need water, and air for oxygen. The best texture for plant growth is called loam, which has all three of the different particle sizes (sand, silt, and clay. The loam allows plants to get a sufficient amount of both water and air.
1a. Observe simple objects and patterns and report their observations.
1d. Compare things and events.
3a. Know science information specified for their grade level.
4a. Record data accurately when give the appropriate form and format.
4b. Report observations with pictures, sentences, and models.
Pre-lab discussion: Tell students they are going to get dirty today! Ask students what soil is and what might they find in soil. Have students list the living, nonliving, and once living materials they believe are found in soil. Expand on the list and discuss the soil facts given in the background information section.
Instructional procedure: Have students complete their student sheet as they work through the activity.
II. What is in our soil?
II. Describe the differences between dry sand, clay and humus.
III. Describe the differences between wet sand, wet clay, and wet humus.
IV. Settling of sand, clay, and humus in water.
Questions to discuss for settling tubes:
Which sample took the longest to settle and why? The clay has the smallest particles so they take longest to settle.
Why do the tubes look different? The particles have different sizes. Sand has the largest particles and settles fast. The humus has medium size particles and settles next. However, the humus will settle into three layers. A top floating layer, the middle clear water layer, and the layer of dirt particles that sinks in the tube. Finally, the clay has the smallest particles and they will settle slowly over a couple of hours.
Do you notice anything changing in the clay tube over 5 minutes? The clay should settle out in order. You should be able to see the largest particles on the bottom because they settle fastest, then the smallest particles won't settle out until much later and they will be on the top.
Soil can be moved naturally from place to place. In nature, settling is always occurring in rivers and streams. As it rains, soil is swept into nearby rivers and streams and is carried along until it can be deposited in a new place. If it's a slow moving river the small particles can be deposited quickly but in a quick moving river or stream the small particles can be carried very far away from where they started. This settling changes our rivers and the land around it.
Rio Tinto Hands-on Science Curriculum Team