Soil Composition
What two main types of material make up most soil?
Weathered rock particles and decomposed organic material.
What is weathering? (short definition)
Weathering is the breakdown of rocks into smaller pieces or chemicals.
What is the top layer of soil, rich in organic matter, commonly called?
O horizon (or topsoil if referring to A with high organic content).
When planning an investigation, what is the first thing you should write? (Hint: it guides the study)
A testable question or hypothesis
Name one use of healthy soil in everyday life.
Grow food, filter water, support buildings, habitat for organisms.
Name one inorganic component and one organic component of soil.
inorganic = sand (or silt/clay/minerals); organic = humus/decomposed leaves.
Name one agent that causes physical weathering.
Example: freeze-thaw, abrasion, plant root growth.
Which horizon contains mostly weathered rock fragments and less organic material?
C horizon (or sometimes B horizon contains more rock fragments than A).
Name one simple way to collect evidence that soil has layers using a clear container.
Make a soil profile in a clear jar (soil column) by carefully layering and observing, or dig a small pit to view horizons.
How does soil help plants that humans grow for food?
Provides nutrients, water retention, and root support.
Which particles in soil are the smallest and hold water best: sand, silt, or clay?
Clay.
How does chemical weathering change rocks into soil?
Chemical weathering dissolves or alters minerals (e.g., acid from rain or roots) turning rock into smaller mineral components.
Put these horizons in order from top to bottom: B horizon (subsoil), O horizon (organic), C horizon (partly weathered rock), A horizon (topsoil).
O, A, B, C.
Describe how you could use sieves or screens to investigate soil composition.
Sieve soil through progressively smaller mesh to separate sand, silt, and clay-sized particles and measure proportions.
Explain one way poor soil quality can harm the environment or human activities
Erosion removing topsoil reduces fertility; contamination harms crops and water.
Explain how decomposed plant material helps soil.
It adds nutrients, improves water retention and structure (humus).
Give one example of erosion moving soil from one place to another.
Water runoff carrying soil, wind blowing dust, or a river transporting silt.
Describe one difference between topsoil (A horizon) and subsoil (B horizon)
Topsoil (A) has more organic matter and nutrients and is darker; subsoil (B) has more clay, minerals, and less organic material.
Provide two pieces of evidence you would record to show soil is made from weathered rock and decomposed organic material.
Evidence examples: visible layered horizons (O, A, B, C) and microscopic/mineral analysis showing rock fragments plus organic pieces; record observations, photos, measurements.
Describe how farmers might change soil structure to improve crop growth
Add organic matter (compost), crop rotation, tillage adjustments, or liming to change pH and structure.
Explain how living organisms can both cause weathering and help form soil.
Minerals come from weathering of parent rock (physical and chemical breakdown).
Explain how living organisms can both cause weathering and help form soil.
Roots break rock (physical); microbes and acids break minerals (chemical); organisms add organic matter when they die.
Explain why the C horizon is important evidence that soil forms from weathered rock.
C horizon shows partly weathered parent rock—direct link between rock and soil formation.
Provide two pieces of evidence you would record to show soil is made from weathered rock and decomposed organic material.
Evidence examples: visible layered horizons (O, A, B, C) and microscopic/mineral analysis showing rock fragments plus organic pieces; record observations, photos, measurements.
Propose a simple conservation practice that helps preserve topsoil and briefly explain why it works.
Practices: cover crops, reduced tillage, contour plowing; they reduce erosion and keep organic matter in topsoil.