What Is the Biosphere?

The biosphere is the global sum of all ecosystems and the regions of Earth where living organisms exist and interact with their physical environment. It extends vertically from the deep ocean floor, including hydrothermal vent communities kilometers below the surface, to the lower stratosphere, where spores and bacteria have been detected above 20 kilometers altitude. Horizontally, it encompasses every continent, ocean basin, and freshwater body where life has been found. The biosphere is defined by the presence and activity of organisms, which continuously exchange matter and energy with the atmosphere, hydrosphere, and lithosphere around them.

The concept was introduced by the geologist Eduard Suess in 1875 and elaborated by the Russian geochemist Vladimir Vernadsky in his 1926 work, where he described the biosphere as a planetary-scale chemical force capable of fundamentally altering Earth's surface chemistry. Vernadsky's framing remains influential in contemporary Earth system science.

Structure and Extent

The biosphere is subdivided into biomes, large-scale assemblages of ecosystems defined by climate, vegetation type, and fauna. Terrestrial biomes include tropical rainforests, temperate grasslands, boreal forests (taiga), tundra, and deserts, each characterized by distinct productivity, species richness, and carbon storage capacity. Marine biomes range from the photic surface zone of the open ocean, which receives enough sunlight for photosynthesis, to the aphotic deep sea. Freshwater biomes include rivers, lakes, wetlands, and estuarine transition zones. Within each biome, ecosystems consist of communities of organisms interacting with one another and with abiotic factors such as temperature, precipitation, and nutrient availability. NASA's Earth Science program research on the biosphere monitors the global extent and productivity of the biosphere using satellite remote sensing instruments including the MODIS and VIIRS sensors.

Biogeochemical Cycles

The biosphere plays a central role in circulating chemical elements between living matter and the abiotic environment. The carbon cycle, in which photosynthetic organisms fix atmospheric carbon dioxide into organic compounds and heterotrophs return it through respiration and decomposition, is the most intensively studied cycle because of its role in regulating Earth's climate. The nitrogen cycle involves fixation of atmospheric nitrogen by specialized bacteria, nitrification, denitrification, and assimilation into proteins and nucleic acids, with the biosphere mediating transformations that purely geochemical processes could not sustain at comparable rates. The phosphorus and sulfur cycles similarly depend on microbial activity to move elements between soil, water, rock, and atmosphere. Disturbances to these cycles, such as excess nitrogen deposition from agricultural fertilizer, produce cascading effects on ecosystem productivity and species composition. The UCAR Center for Science Education overview of the biosphere places biogeochemical cycling in the context of Earth's climate system.

Interaction with Other Earth Systems

The biosphere is one of four major Earth system spheres, alongside the lithosphere (solid Earth and soils), hydrosphere (water), and atmosphere (gases). These spheres exchange energy and matter continuously: vegetation transpires water to the atmosphere, weathering of rocks by lichens and plant roots releases minerals to soils, and ocean phytoplankton produce dimethylsulfide gases that influence cloud formation. Feedbacks between the biosphere and climate are a central subject of Earth system modeling. Rising temperatures alter species ranges, phenology, and primary productivity; in turn, changes in vegetation cover affect surface albedo and evapotranspiration, feeding back on local and regional climates. The Aspen Global Change Institute's resources on the biosphere document how these feedbacks are measured and incorporated into coupled climate-biosphere models.

Applications

The biosphere concept has applications in a range of fields, including:

• Climate modeling: representing land-surface and ocean biological feedbacks in Earth system models
• Conservation biology: identifying biodiversity hotspots and designing protected area networks
• Remote sensing: monitoring global vegetation indices, ocean color, and land cover change
• Carbon accounting: estimating terrestrial and oceanic carbon sinks for climate policy
• Astrobiology: using the biosphere as a template for detecting life on other planetary bodies