Soil Formation U2L5

Susan rubs two rocks together. One of the rocks wears away to form small particles. What would most likely happen if this rock continues to break into small pieces after Susan puts the rocks back on the ground?

• The pieces may become part of the bedrock.

• The pieces may become part of the soil.

• The pieces may become part of the ice wedging process.

• The pieces may become part of the organic matter in the soil.

Gopher tortoises live on dry land. They live in large holes that they dig in the soil. Which statement gives the best explanation of how this behavior aids in soil formation?

• It hardens the soil, allowing less water to reach the rocks underground.

• It erodes the soil by moving it from underneath the ground to above ground.

• It loosens and mixes the soil, increasing air in the soil and the ability to drain water.

• D. It causes weathering of the rocks, as the tortoise breaks the rocks into smaller pieces.

Which of the following describes how microorganisms influence the chemical characteristics of soil?

• They loosen and mix the soil by digging burrows underground.

• They add inorganic material to the soil by weathering rocks on Earth’s surface.

• They add moisture to the soil by creating pores through which water can move.

• They add organic material to the soil by breaking down the remains of plants and animals.

What is humus?

• dark, organic material formed in soil from the decayed remains of plants and animals

• a loose mixture of rock fragments, organic material, water, and air that can support the growth of vegetation

• spaces between soil particles through which water and air can move

• weathered sediment broken down by atmospheric forces on Earth’s surface

Which soil horizon is primarily responsible for this soil’s fertility?

• Horizon A, because it contains humus and other organic nutrients that plants need.

• Horizon B, because plant roots can grow down into the smaller rock fragments.

• Horizon C, because most of the groundwater is stored in this horizon.

• Horizon D, because it is the parent rock that breaks up to form soil