The Earth’s Soil
Let's begin our study of the Earth’s lithosphere by examining the portion of it that we are most familiar with: the soil. Soil is found on the upper most layer of the Earth.
Soil consists of a mixture of weathered rock, finely ground into powder, minerals, and a variety of living and dead lifeforms. This nutrient rich layer typically only extends downward a few feet, about as deep as plant roots extend.
Soil contains all the nutrients needed by plants to survive. Some areas, such as deserts, have very poor soils. In these locations, it is difficult for complex plant life to take hold. Believe it or not, tropical rain forests also have poor soils. This is because most of the nutrients are already within living plants.
The Earth’s soil has developed over hundreds of millions of years, as the forces of weather have ground the top rocky layer of the Earth into smaller and finer grains, and as plant and animal life has helped to deposit nutrients.
An important part of soil is the part that is alive. Many different bacteria, algae and fungi do important jobs that make life possible. Without these basic lifeforms performing these important roles, more complex lifeforms could not survive.
The soil beneath our feet typically has a darker color than the dirt, or regolith, beneath it. This darker color is caused by the plants and animals, both living and dead, that are found within it.