The freezing and thawing helps to crack and break the rocks. Bacteria, fungi, lichens and other soil-formers break down rocks. Dead plants furnish organic matter for soil. Topsoil has organic material, leaf litter, and humus. Living organisms as well as organisms that cause decay live in this layer.
Subsoil consists of rock particles mixed with mineral nutrients.
The lowest deepest layer consists of fragments of the parent bedrock. Types of soil are classified according to their organic content, mineral composition, pH, and size of rock particles. Different types of plants grow best in different types of soil. The biosphere , the part of the earth where we live is about 20 km thick. It extends from the ocean floor to the highest point in the atmosphere where life is found.