Show students a container of soil and ask if they recognize the contents. Affirm that it is dirt — or as scientists say: soil — and that it’s a very important earth material.

• How would Earth be different if it was just solid rock, if there were no soil?

• no land plants
• no life on land

As students consider the importance of soil, introduce the investigation question.

What is soil made of?

Let students brainstorm some ideas, supporting questions might include

• Where does soil come from?
• Are rocks or minerals involved?
• Is the soil in your backyard the same as the soil in the desert?
• If you dig a hole a foot deep, is the soil at the top the same as the soil at the bottom?

Continue the discussion until a consensus emerges that soil is not a single material, but some combination of materials that appear in very small pieces, and that soils differ from place to place.

Recall the last two investigations, when students observed rocks and minerals using their senses and their magnifiers. Let students know that today they will observe two soil samples, record their observations, and consider what soil might be made of.