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 forms mostly from the rocks that lie beneath it. These rocks can be sedimentary, igneous, or metamorphic, and they shape the soil that grows above them. The type of rock and how it was formed depend on the area’s geology, guided by ideas about how Earth’s plates move, shift, rise, sink, and build up layers over time.

Different rocks affect soil in various ways. Some rocks, like those changed by heat and pressure, are rich in silica. Others, such as certain volcanic rocks, also have lots of silica but break down faster, allowing more nutrients to spread. Rocks with high silica create a special kind of acid when they weather. Only a few rocks add important nutrients like phosphorus and nitrogen to the soil. Some special kinds of rock, formed in deep ocean water, hold onto these nutrients well. Other rocks, made mostly of minerals that dissolve easily, release useful elements into water around them.

Weathering and dissolution of minerals

Soil forms mainly when rocks break down through chemical weathering. This process is helped by plants and a special kind of acid made from air and water. This acid, called carbonic acid, breaks down different kinds of rocks and minerals.

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

Biosphere

The biosphere plays an important role in creating and changing soil. Tiny plants and microorganisms, like lichen, can start breaking down rocks. These tiny living things release special acids that help turn rocks into soil. Over time, more plants and animals move into the soil. Animals like earthworms help 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 a lot on redox conditions. When just a little water covers the soil, special bacteria use up the oxygen, which 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 something called reduction potential. This helps us understand how nutrients move in wet areas. Scientists can study very old rocks to learn about the oxygen levels in ancient soils. By looking at the forms of iron in these rocks, they discovered that oxygen levels dropped a lot during a time called the late Permian, which 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, which makes the soil a bit more acidic than the air. Some gases from the soil go up into the air, like the results of breaking down rocks, rotting things, and tiny plants making food.

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

Soil in forests

Soil in forests is very rich and thick because of the layers of dead leaves and plants on the ground. Many large trees and animals live in forests, making 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 a lot of direct sunlight and rain throughout the year, more than any other place on Earth. Because of the warm temperatures, sunlight, and rain, these forests grow a lot of plants and trees. This leads to the creation of up to 800 grams of carbon for every square meter each year. The heat and water also make the soil break down faster, which changes its chemistry. Because of this, tropical forest soil looks different from soil in cooler forests. Instead of having clear layers, the soil often has a rusty red color from certain minerals.

Soil in grasslands and deserts

In grasslands, rain is about the same as or less than what plants and soil lose through evaporation. This means soil doesn't get washed away much. Instead, minerals like calcium build up near the top. In places where it doesn't rain much and evaporation is high, water doesn't move deep into the soil, so the soil doesn't change much. In areas where there is more rain, clay moves deeper into the soil. When rain is low, calcium turns into a rock-like layer called caliche deeper in the soil.

Deserts are similar to grasslands but are always dry because there is almost no rain. Here, soil changes even slower. Below the caliche layer, you might find minerals like gypsum and halite. Scientists study desert soils to understand how they form over time. They found that a nutrient called phosphorus disappears quickly, and carbon builds up slower, which affects how plants and animals use these nutrients.