Name: soil layers and how soil forms
Uploaded: 2026-08-26T08:21:04.082Z
Duration: 3 min 6 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth and Human Activity

ESS.EES.6.1

The Soil Ecosystem

Soil, often called Earth&#x2019;s skin, is more than just dirt.It is a complex ecosystem made of abiotic factors, such as inorganic minerals, air, and water, and biotic factors, including microorganisms such as bacteria and fungi, as well as larger organisms such as plants, rodents, and earthworms.Inorganic minerals make up 40 to 45% of soil volume. They enrich the ecosystem with nutrients such as nitrates, phosphates, and potassium.Air and water together make up 50 to 55% of soil volume. Air enriches soil with gases such as oxygen, nitrogen, and carbon dioxide. Water helps dissolve nutrients and move them through the soil.Organic matter, including living and dead organisms, makes up about 5% of soil. These organisms interact with each other and with abiotic factors to recycle nutrients.Soil forms distinct layers called horizons. The O horizon is the top organic layer and is rich in decomposed plant and animal material.Just below it lies the A horizon, also known as topsoil. This layer is especially important for plant growth because it contains minerals mixed with humus.Humus forms when microbes break down dead plants and animals. It adds nutrients to the soil and improves water and air retention. These features create a soft, porous soil structure that supports the growth and survival of plants and many soil organisms.The texture and composition of topsoil make it ideal for seed germination and plant growth. Healthy soil is fertile and serves as an important natural resource for agriculture. But nutrient use can reduce soil fertility over time.The soil ecosystem can restore nutrients through processes like the breakdown of organic matter. These natural processes are called ecosystem services.Human activities can disrupt this balance. Pollution can build up faster than soil can recover. For example, microplastics form when plastic waste breaks into smaller pieces. These particles can harm soil organisms, change soil structure, and affect nutrient cycling.As climate change affects soil systems and the demand for food increases, careful soil management and conservation are needed to support life on Earth.

the soil ecosystem

Plants obtain inorganic minerals and water from the soil, which acts as a natural medium for land plants. The composition and quality of soil depend not only on the chemical constituents but also on the presence of living organisms. In general, soils contain three major components:<ol><li>Inorganic mineral matter, which constitutes about 40 to 45 percent of the soil volume.</li><li>Organic matter, also known as humus, which makes up about 5 percent of the soil volume.</li><li>Water and air, covering about 50 percent of the soil volume.</li></ol>Healthy soil has an adequate quantity of air, water, minerals, and organic matter to promote plant growth.Based on its physical structure, the soil is composed of four distinct layers:<ol><li>O-horizon or topsoil</li><li>A-background</li><li>B-horizon or subsoil</li><li>C-horizon or base soil</li></ol>O-horizon comprises freshly decomposing organic matter - a result of the decomposition of plants, animals, or microorganisms. It is also known as topsoil. This humus layer is significant in improving soil fertility, moisture, and air retention. Though the humus is a smaller percentage of the overall soil volume, it is nevertheless essential.A-background is a mixture of organic and inorganic components and is the beginning of true mineral soil formed by the weathering of rock.The B horizon, or subsoil, is a layer of fine clay that is less fertile than the topsoil. It is rich in moisture and displays less biological activity than the topsoil.The C horizon comprises the underlying weathered rock. Beneath the C horizon generally lies the bedrock that acts as a parent material in soil formation.Soil FormationSoil forms as a consequence of physical, chemical, and biological weathering processes acting on the parent bedrock material. In the case of physical weathering, the earth forms from mechanical actions such as temperature change, wind, frost, abrasion, or earthquakes, any or all of which can cause the breakdown of the bedrock. In chemical weathering, the bedrock reacts with water, acid, or other chemical components. Biological weathering, in contrast, is influenced by burrowing animals and plant roots that grow into the cracks of the rock, making it split.Overall, the type of soil that will be produced is governed by five major interacting factors - composition of the parent material, the type of living organisms present, the climatic conditions, topography, and time. Interaction among these factors produce an infinite variety of soils across the earth.

Plants obtain inorganic minerals and water from the soil, which acts as a natural medium for land plants. The composition and quality of soil depend not ...

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Education

JoVE Core

Biology

Plant Biology

Plant Structure, Growth and Function

KEY TERMS AND CONCEPTS

soil layers and how soil forms

Soil supplies plants with water and inorganic minerals. It is the natural medium for land plants, and its quality depends on both chemical makeup and living organisms in the soil. Healthy soil contains enough air, water, minerals, and organic matter to support plant growth.

Soil is made of three major components. Inorganic mineral matter makes up about 40 to 45 percent of soil volume. Organic matter, also called humus, makes up about 5 percent. Water and air fill about 50 percent of the volume.

Soil also has four distinct layers based on its structure. The O-horizon, or topsoil, contains freshly decomposing material from plants, animals, and microorganisms. This humus layer helps improve soil fertility, moisture, and air retention. The A-horizon is a mixture of organic and inorganic material. It is the start of true mineral soil formed by rock weathering.

The B-horizon, or subsoil, is a layer of fine clay. It is less fertile than topsoil, but it is rich in moisture. It also has less biological activity than the upper layers. The C-horizon is the weathered rock below the subsoil. Under the C-horizon is bedrock, which serves as the parent material for soil formation.

Soil forms through physical, chemical, and biological weathering of bedrock. Physical weathering includes temperature change, wind, frost, abrasion, and earthquakes. Chemical weathering happens when rock reacts with water, acid, or other chemical components. Biological weathering is caused by burrowing animals and plant roots that split rock as they grow into cracks.

The kind of soil that develops depends on five interacting factors: parent material, living organisms, climate, topography, and time. These factors work together to create many different soils across the Earth.

Soil Layers and How Soil Forms

introduction to plant diversity

Plant Adaptations for Life on Land

Plant adaptations for life on land explain how Kingdom Plantae moved from water to land about 410 million years ago. This shift happened when green algae began colonizing a new environment that had not been widely occupied. Land offered more light and carbon dioxide for growth, but it also created major challenges for early plants. One key adaptation was the cuticle, a waxy outer layer that helps prevent water loss. It traps moisture inside the plant. But it also limited direct gas exchange...

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basic plant anatomy: roots, stems, and leaves

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Plant Growth from Root and Shoot Tips

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Root and Shoot Growth: Length vs. Width

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How Roots Absorb Water and Minerals

Roots absorb water and minerals from the soil using specialized tissues. Their branching patterns help them reach more soil, and root hairs on the outer cells increase surface area for contact with the ground. Water enters roots passively because the water concentration in the soil is higher than in root tissue. Minerals move in a different way. They are taken up actively by root cells, which requires energy and transport proteins. Soil particles carry a negative charge, so positive ions...

short-distance transport of resources

Plant Cell Membranes and Water Balance

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xylem and transpiration-driven transport of resources

xylem-and-transpiration-driven-transport-of-resources

How Xylem Moves Water in Plants

Xylem moves water and dissolved minerals from the roots to the rest of the plant. The cells that carry xylem sap are dead when mature, so the flow is passive. Xylem transport depends on special tracheary elements, which connect directly with the extracellular space in the apoplast. There are two main tracheary elements: tracheids and vessel elements. Tracheids are long cells with lignified walls and small pits. These pits let xylem sap move from one cell to the next where the walls overlap.

regulation of transpiration by stomata

How Guard Cells Open Plant Stomata

How guard cells open and close plant stomata controls gas exchange in leaves. A stoma is a tiny opening in the leaf epidermis. The word comes from the Greek word for “mouth.” These openings let plants take in carbon dioxide for photosynthesis and release oxygen into the air. Each stoma is surrounded by two guard cells. When these cells take up water, they create an opening. Ion transport controls how much water stays in the guard cells. A trigger causes pumps to move hydrogen ions out of the...

adaptations that reduce water loss

Plant Features That Limit Water Loss

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phloem and sugar transport

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Soil supplies plants with water and inorganic minerals. It is the natural medium for land plants, and its quality depends on both chemical makeup and living organisms in the soil. Healthy soil contains enough air, water, minerals, and organic matter to support plant growth. Soil is made of three major components. Inorganic mineral matter makes up about 40 to 45 percent of soil volume. Organic matter, also called humus, makes up about 5 percent. Water and air fill about 50 percent of the volume.

key elements for plant nutrition

Plant Nutrients: Macro and Micro Needs

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the roles of bacteria and fungi in plant nutrition

the-roles-of-bacteria-and-fungi-in-plant-nutrition

How Soil Microbes Help Plants Get Nutrients

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the apoplast and symplast

Plant Water Transport Pathways

Plant water transport pathways help roots absorb water and dissolved minerals from the soil. These pathways move materials through plant tissues that support growth and nutrient uptake. The main tissue regions involved are the apoplast and the symplast. The apoplast includes everything outside the plasma membrane of living cells. It contains cell walls, extracellular spaces, xylem, phloem, and tracheids. The symplast is the cytosol of all living plant cells, along with the plasmodesmata that...

key terms and concepts

Explore soil layers, soil composition, and the weathering processes that form soil. Learn how humus, subsoil, and bedrock support plant growth.

Soil Layers and How Soil Forms | JoVE K12

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Soil Layers and How Soil Forms

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