Soil

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Soil Noun

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[soil]

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Soil

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A dynamic natural resource on the Earth's surface, composed of minerals, organic matter, water, and air that supports plant life.

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Example: This diagram shows a cross-section of soil, revealing its distinct layers called horizons, from the organic matter on top down to the bedrock below.

Front

Weathering Noun

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[weth-er-ing]

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Weathering

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The physical and chemical process that breaks down rocks and minerals at the Earth's surface, initiating the formation of soil.

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Example: A tree's roots grow into a crack in a rock, forcing the crack to widen and break the rock apart. This is called biological weathering.

Front

Humus Noun

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[hyoo-muhs]

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Humus

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The dark, organic component of soil, formed by the decomposition of plant and animal remains by various soil microorganisms.

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Example: This diagram shows that humus is the top, dark layer of soil, rich in decayed organic matter, located just below the surface vegetation.

Front

Pioneer Organisms Noun

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[pai-uh-neer or-guh-niz-ums]

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Pioneer Organisms

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The first species, such as lichens and mosses, to colonize previously barren environments, beginning the process of soil formation.

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Example: Pioneer organisms, like these small ferns, are the first species to grow on new, barren ground like this hardened lava, starting the process of soil formation.

Front

Soil Profile Noun

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[soil proh-fail]

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Soil Profile

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A vertical cross-section of the soil from the ground surface downwards to where the soil meets the underlying parent material.

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Example: This diagram shows a soil profile, which is a vertical cross-section of the ground, revealing distinct horizontal layers from organic matter down to bedrock.

Front

Horizon Noun

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[huh-rai-zuhn]

Back

Horizon

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A distinct layer of soil, parallel to the surface, with physical and chemical characteristics that differ from layers above and below.

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Example: This diagram shows a cross-section of soil, illustrating the distinct layers, or horizons (O, A, B, C), that form from the surface down to parent material.

Front

Topsoil Noun

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[top-soil]

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Topsoil

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The uppermost layer of soil, typically rich in organic matter and microorganisms, making it the most fertile for plant growth.

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Example: This diagram shows topsoil as the layer below the organic material and above the subsoil, rich in minerals and nutrients where plants grow.

Front

Subsoil Noun

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[sub-soil]

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Subsoil

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The layer of soil under the topsoil, characterized by an accumulation of clay and minerals leached from the layers above.

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Example: This diagram shows a cross-section of soil, identifying the subsoil (B horizon) as the layer located below the surface soil and above the substratum.

Front

Parent Material Noun

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[pair-uhnt muh-teer-ee-uhl]

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Parent Material

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The underlying geological material, such as weathered rock or sediment, from which a soil is formed and develops its properties.

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Example: This diagram shows the layers of soil. The 'Parent material' (Layer C) is the weathered rock and mineral layer from which the upper soil horizons develop.

Front

Bedrock Noun

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[bed-rok]

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Bedrock

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The solid, unweathered rock that lies beneath the surface soil and parent material, forming the base of the Earth's crust.

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Example: This diagram shows the different layers of soil, with bedrock being the solid, unweathered rock layer found at the very bottom.