If you took a handful of soil, more microorganisms reside in the soil than people on Earth.

Soil are compound mixtures found at the upper most layer of the surface of the Earth. It is mostly loose materials that are composed of rock, minerals, water, and decaying plant and animal matter. Soil has all the nutrients and raw materials needed for the growth of plant life. Plants are vital for the continuation of life on Earth; hence soil is an essential material for life as well. Soil provides shelter for many different animals as dig into it and use it for their needs. Soil also has a natural capacity to filer and clean water which is a crucial compound for life.

Soil is composed of five distinctive layers. The topmost layer is composed of the remains of leaves and twigs. This organic material provides plenty of nutrients for plants. Just below that layer is topsoil which is where a variety of minerals are located. Subsoil is found beneath topsoil which is mostly clay and minerals. Large rocks are found beneath the subsoil they provide a foundation for all layers that sit on top of it. The primary foundation is located below this and is called the bedrock.

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What is Soil?

It takes a very long time for soil to form, and the formation of soil depends on different factors, including the topography of the land and the climate where the soil is forming.

What is Soil? Questions

There are different kinds of soil with different characteristics. One of the main ways that kinds of soil differ is in their texture: is it more like sand, silt, or clay?

Soil Horizons

Soil is composed of layers that we call horizons. Different kinds of soil have different numbers of horizons.

QUESTIONS: Soil Horizons

In which horizon do plants and other organisms make their home?

Functions of Soil

Soil is where nutrients on Earth are recycled, including important nutrients like carbon and nitrogen.

QUESTIONS: Functions of Soil

Different kinds of soils in different locations may absorb, hold, release, change, and/or purify Earth’s water. Soil also filters water.


Over millions of years, erosion shapes the landscape. Erosion can form hills when displaced material gets shifted and piled up somewhere else.


Why is erosion a problem for farmers?

What Lives in the Soil?

Decomposers produce enzymes that break down plant and animal waste laying on the surface of the Earth into smaller parts.

QUESTIONS: What Lives in the Soil?

Soilborne diseases like Rhizoctonia canker, black dot, Verticillium wilt, and common scab can make plants sick and unsuitable for eating.


Because they are available in small amounts and only needed by living organisms in small amounts, we call these nutrients trace elements.

QUESTIONS: Nutrition

What's wrong with monoculture?


The process by which water reaches the subsoil where plant roots are located, as well as the movement of water down past the root zone, is called permeability.


Ponding is the holding back or damming up of water to form a pond or small lake.


Organisms that participate in the decomposition process are called decomposers. There are more than a hundred thousand kinds of decomposers.

QUESTIONS: Decomposition

What is the relationship between climate change and decomposition?

Food Security

Erosion can pull valuable nutrients out of the soil and concentrate them in other areas, for example, in bodies of water, the quality of which then becomes compromised.

QUESTIONS: Food Security

Which of the following is NOT a consequence of excess salinity?

Human Health

We say that we have food security when everyone has enough safe and nutritious food to eat.

QUESTIONS: Human Health

What four major elements make up 99% of the human body?