Pedosphere

The pedosphere is the top layer of the Earth's crust made of soil. It forms where the air, water, rocks, and living things all work together. Think of it like the skin on the outside of the Earth’s surface. It is only found where these parts interact, creating the soil we see.

This layer is very important because it helps control how air, water, and living things move and change chemicals. It is part of a bigger area called the Critical Zone, which includes plants, soil, underground water, and rocks. The place where soil forms depends on where it is on the globe, because weather, rocks, plants, and human actions all change from place to place.

Soil starts forming when rain, wind, and living things break down rocks. Plants and tiny organisms help speed this up by making acids that break rocks apart. Over time, the soil changes from the original rocks and becomes a home for many plants and animals. This process creates the rich, brown soil that supports forests, gardens, and many living things.

Lithosphere

Main article: Lithosphere

Soil comes from the rocks below it. These rocks can be sedimentary, igneous, or metamorphic. They shape the soil above them. The type of rock depends on the area's geology and how Earth's plates move over time.

Different rocks affect soil in many ways. Some rocks, changed by heat and pressure, are rich in silica. Other rocks, like volcanic rocks, also have silica but break down faster. This lets more nutrients spread. Rocks with high silica can create a special kind of acid when they weather. Only a few rocks add important nutrients like phosphorus and nitrogen to the soil. Some rocks formed in deep ocean water hold these nutrients well. Other rocks, made of minerals that dissolve easily, release useful elements into nearby water.

Weathering and dissolution of minerals

Soil forms when rocks break down. This happens through a process called chemical weathering. Plants help this process. A special kind of acid forms from air and water. This acid is called carbonic acid. It breaks down different kinds of rocks and minerals.

When carbonic acid meets certain rocks, it makes new substances. It can also release minerals into water. For example, it can change feldspar into clay. This process creates bubbles of gas and changes how iron behaves in the soil. This affects the soil’s color and chemistry.

Biosphere

The biosphere helps create and change soil. Tiny plants and microorganisms, like lichen, start breaking down rocks. These tiny living things release acids that turn rocks into soil. Over time, more plants and animals come into the soil. Animals like earthworms make the soil healthier by mixing it up and adding rich material. Larger animals also affect the soil by moving around and leaving behind nutrients.

Redox conditions in wetland soils

Nutrient cycling in lakes and freshwater wetlands depends on redox conditions. When only a little water covers the soil, special bacteria use up the oxygen. This creates conditions where they need to find other ways to get energy. This leads to processes that release gases like nitrogen, hydrogen sulfide, and methane into the air.

The chance of certain chemical reactions happening in soils without oxygen is described by reduction potential. This helps us understand how nutrients move in wet areas. Scientists can study very old rocks to learn about oxygen levels in ancient soils. By looking at the forms of iron in these rocks, they discovered that oxygen levels dropped a lot during the late Permian. This may have played a part in a big event that changed life on Earth long ago.

Atmosphere

In the pedosphere, the air and gases are balanced with the air above us. Plants and tiny living things in the soil release something called CO₂. This makes the soil a bit more acidic than the air. Some gases from the soil go up into the air. These gases come from breaking down rocks, rotting things, and tiny plants making food.

The air gives us things like dust and tiny bits carried by wind. Rain often carries a lot of nitrogen. Nitrogen is important for plants to grow.

Soil in forests

Soil in forests is rich and thick because of the layers of dead leaves and plants on the ground. Many big trees and animals live in forests, keeping the soil healthy. When it rains more than what evaporates, water moves down through the soil. This slow movement helps create special chemicals that change the soil. As water moves down, it carries some parts of the soil with it, making the layers look and act differently.

Soil in the tropics

Tropical forests get lots of direct sunlight and rain all year, more than anywhere else on Earth. The warm temperatures, sunlight, and rain help these forests grow many plants and trees. This creates up to 800 grams of carbon for every square meter each year. The heat and water also make the soil break down faster, changing its chemistry. Because of this, tropical forest soil looks different from soil in cooler forests. Instead of clear layers, the soil often has a rusty red color from certain minerals.

Soil in grasslands and deserts

In grasslands, there is not much more rain than what plants and soil lose to evaporation. This helps keep the soil stable. Minerals like calcium collect near the surface. In dry places with little rain and high evaporation, water does not go deep into the soil, so the soil changes very little. Where there is more rain, clay moves deeper. When rain is scarce, calcium forms a hard layer called caliche deeper in the soil.

Deserts are like grasslands but are always dry because there is almost no rain. Soil in deserts changes even more slowly. Below the caliche layer, you can find minerals such as gypsum and halite. Scientists study desert soils to learn how they form over long periods. They discovered that a nutrient called phosphorus disappears fast, and carbon builds up slowly, which influences how plants and animals use these nutrients.