Biosphere

The biosphere includes all known living organisms and the places where they live, from soils and forests to ocean waters and some parts of the atmosphere. It overlaps the geosphere, hydrosphere and atmosphere: life occupies portions of solid ground, water and air. Its boundaries are therefore ecological rather than a sharply defined physical layer. Nearly all life is concentrated in a relatively narrow range of environments where temperature, water, nutrients and other conditions permit survival. The biosphere is commonly described as a global system made up of many interacting ecosystems, each involving organisms and their physical environment.

Most ecosystems receive energy ultimately from sunlight. Photosynthetic organisms use light to build energy-rich organic compounds, which support food webs as organisms consume plants, algae or other animals. Energy passes through ecosystems and is dissipated, while chemical elements are recycled. Respiration, excretion and decomposition move carbon and other materials between organisms, soil, water and the atmosphere. In this way, the biosphere is linked to wider biogeochemical cycles rather than operating in isolation.

Living organisms both respond to and influence conditions in the atmosphere, oceans and land. For example, photosynthesis transfers carbon dioxide from the atmosphere into organic matter, while respiration and decomposition return carbon to the environment. The ocean also exchanges carbon with the atmosphere, and carbon can remain stored in deep water, sediments and rocks for very different lengths of time. These connections mean that changes in one part of the Earth system can affect ecological conditions elsewhere. Human activities such as burning fossil fuels and changing land use alter material flows that sustain and interact with the biosphere.

The term biosphere describes Earth's life-supporting global system; an ecosystem is a more local or regional unit within it. UNESCO’s Man and the Biosphere Programme uses the name in a different, institutional sense: biosphere reserves are designated places intended to connect biodiversity conservation with sustainable development and learning. A reserve is not the whole biosphere, nor does the designation by itself guarantee that ecological pressures or community concerns have been resolved. Understanding the biosphere therefore involves both ecological processes and the ways human societies depend on and affect them.