The biosphere is defined as the layer of land, water and air towards the outer surface of the Earth in which living things are capable of surviving. It includes both the living things found on Earth and the non-living elements that support them. The non-living part of the biosphere is divided into three subdivisions, the lithosphere, hydrosphere and atmosphere.
The lithosphere, hydrosphere and atmosphere interact to make life possible within the biosphere. The lithosphere is the rocks and soil that form the solid portion of the Earth's crust. Minerals that are essential for life are ultimately derived from the lithosphere. They are absorbed first by plants, or producers, and travel up the food chain as these organisms are consumed by others. The hydrosphere is defined as the liquid portion of the Earth's surface. Water fills the lakes, oceans, ponds and rivers, and it is essential for all forms of life on Earth.
The atmosphere is the gaseous portion of the biosphere, and it is subdivided into four layers. The troposphere is the lowest level, extending approximately 15 kilometers above the Earth's surface. All life is confined to this atmospheric level. The outer three layers, known as the stratosphere, ozonosphere and ionosphere, prevent certain harmful rays from reaching the troposphere.