This week we had a great time playing with dirt! Scientifically we like to call it soil, not dirt, and the young scientists used their inquisitive minds to examine what exactly is in soil and it comes from. We learned that soil and rocks are similar, expect that rocks go under pressure and heat. Students also learned about the ecological, biological and topological factors that contribute to soil formation over hundreds and thousands of years. For example, many of us know that rocks will eventually erode into tiny pieces that become soil. But others of us might not appreciate the role that microorganisms play in soil formation (they help break down organic material such as leaves and other dead bugs) or that soil contains large amounts of air and water.
We looked at the 3 different types of soils (sand, silt, and clay) and focused on the texture and color. Students collectively described their observations to each other. These three types of soils, along with organic matter, combine to create soil we find in nature.
Experimentally, students examined clay, sand, topsoil, and sphagnum moss (an additive to soil). They noticed differences in the soil colors and were able to correlate that color to what is in the soil itself. We tried to see which soils had more of sand, silt, clay, and humus. Dark brown/black soils tend to contain lots of broken down organic material, sandy soils tend to contain many mineral fragments and even parts of shells, and red toned soils might contain high amounts of iron. We learned that the soil needs to have access to oxygen, in order for the iron to “rust” and turn this red-ish color. Students also observed the texture of the soils noting that some soils contain smaller particles than others. Finally, students observed how well soils can hold, or not hold, water. We learned that clay holds onto water the most, but also takes the longest time to absorb. Moss absorbed the most water (from everything we tested), which is why it’s a great additive to soil. Sand held onto water the least, which is also why it is difficult to grow plants (though some plants love this type of soil!). All of these factors (color, texture, water handling ability) are important in determining how healthy a soil might be for growing crops or how productive soil might be in filtering out impurities from water.
Feel free to look more closely at the soil in your own yard now and see what you can find!