Compare soil and rock using observations and fair tests

Learning goal: Describe Earth's nonliving resources using observable properties and compare soil samples through a controlled drainage investigation. Soil, rocks, air and water are resources used by living things and people. Calling them nonliving does not mean they are unimportant. Soil also contains living organisms, but the soil material being studied includes nonliving components.

Soil is a mixture of pieces of rock, organic material, water and air. Organic material includes remains of once-living things. A soil sample can contain visible plant fragments and particles of different sizes. Water and air occupy spaces between solid pieces. Soil is more than a pile of crushed rock, and different samples need not have the same composition. Scientists call this mixture soil, not dirt. The two words do not mean the same thing: in everyday speech dirt often means something unclean, such as mud tracked onto a floor, while soil names the mixture of rock pieces, organic material, water and air that can be observed and measured and in which plants grow. Use the word soil in your records.

Observe teacher-approved samples with a hand lens. Record color, visible particle sizes, texture and moisture. Use descriptive words such as rough, smooth, crumbly or damp, and distinguish what you observed from what you inferred. A dark color alone does not establish exactly which materials are present or whether a soil is best for every plant. Do not taste samples; wash hands after handling them.

Compare rocks by visible color, texture and grain size or shape where grains are visible. A rock with a smooth outer surface can still have grains inside that surface. Rocks form in different ways. Some form when melted rock cools and hardens; some form when pieces of sand, mud or shell are pressed and cemented together; and some form when existing rock is changed by great heat and pressure deep underground. Observable characteristics can give clues about how and where a rock formed. A rock made of rounded sand grains stuck together suggests grains that were moved and worn by water or wind; a rock containing pieces of shell suggests it formed where those shelled animals lived, often under water. These are clues to investigate. This lesson does not ask learners to assign formal rock classes from appearance alone. A sorting rule should use an observable property and be applied consistently to every sample.

To investigate drainage, place equal amounts of two soil samples in matching teacher-prepared containers with identical drainage openings and filters. Put a collecting cup under each. Add the same amount of water to each sample over the same time interval. Measure water collected after the same waiting time. Keep the container design, soil amount, initial moisture conditions and added water as similar as practical.

The amount collected describes water that passed through during the observation period. If less water appears below one sample, more may remain in that sample at that time. Do not conclude that water vanished. Some could also remain on the apparatus or spill, so record procedural problems. The initial moisture and how tightly soil was packed can influence drainage; they are not harmless details to ignore.

Repeat the comparison before drawing a conclusion. A single run may be affected by a blocked opening or uneven pouring. Use the observed data to explain which tested sample drained more quickly under the stated conditions. Avoid claiming that every sample with the same color will behave the same way. Soil properties vary, and a small test supports a limited conclusion.

Worked interpretation of fictional data: Two samples each receive one hundred milliliters of water. After the same waiting time, cup A collects seventy milliliters and cup B collects thirty. Sample A allowed more water to pass through in that period. The difference is forty milliliters. These are invented practice results, not observations of the reader's samples.

Check the reasoning: A learner says B is automatically the best gardening soil because it drained less. That conclusion needs more information. Plants have different water needs, and roots also need suitable conditions. Drainage is one useful property, not the only criterion for plant growth or building decisions.

Guided investigation: Plan the comparison before collecting data. Sketch the apparatus, name the changed variable and list the features kept consistent. Record actual measurements, repeat trials and note anything that made the trials difficult to compare. Draw the observed samples and label visible components without claiming that invisible materials were directly seen.

Independent evidence: Sort several rocks by an explicit property and explain the rule. Use a drainage table to support a claim, then name a limitation and a next investigation. If the two setups differ in several important ways, redesign the comparison instead of attributing the result entirely to soil type.