Biosphere

The biosphere represents the totality of life on Earth, encompassing all ecosystems and the interactions that sustain them. Often described as the Earth’s “zone of life”, it forms a thin but continuous shell that includes the land surface, oceans, lower atmosphere and subsurface regions capable of supporting living organisms. Although it is virtually a closed ecological system in terms of matter—exchanging negligible amounts of material with outer space—it remains open to the influx of solar energy that drives photosynthesis and supports global biological productivity.

Conceptual Development and Terminology

The term biosphere was introduced in 1875 by the Austrian geologist Eduard Suess, who defined it as the region of the Earth where life exists. The conceptual framework developed further in the early twentieth century, most notably through the work of Vladimir Vernadsky. He viewed the biosphere as a planetary-scale ecological system shaped by the interplay between living organisms and Earth’s physical spheres: the lithosphere, atmosphere, hydrosphere and cryosphere. Vernadsky also positioned ecology as the scientific study of the biosphere itself, reflecting its interdisciplinary nature spanning geology, astronomy, climatology, biology and the environmental sciences.
By the 1960s, the word ecosphere emerged to describe the combined biological and physical components of Earth functioning together as a single planetary system. The field of biospherics—the study of artificial Earth-like biospheres and closed ecological models—soon developed in conjunction with experimental and space-related life-support research.

Scientific Definitions and Components

In geochemical terms, the biosphere is defined as the complete global biomass: the total mass of living organisms, also referred to as the biota. Alongside the geosphere, hydrosphere and atmosphere, it forms one element of the four-sphere model used to describe Earth’s integrated systems. When these components operate together as a single unit, they form the planetary ecosphere.
The biosphere consists of an immense diversity of life forms, each interacting with physical environments to create stable ecosystems. It includes terrestrial, freshwater, marine and subterranean habitats, as well as zones far above and below the Earth’s surface where extremophiles persist under extraordinary conditions.

Origin and Evolution of Life within the Biosphere

Current scientific understanding suggests that the biosphere began forming at least 3.5 billion years ago, following the emergence of early life. Key evidence includes biogenic carbon signatures in ancient rocks from Greenland and microbial mat fossils in Australian sandstone. More recent discoveries propose that fossil-like microorganisms in very old hydrothermal deposits may date back more than 4.2 billion years, implying the rapid emergence of life not long after the formation of Earth’s oceans.
The speed at which life appeared has led some researchers to suggest that life might also arise readily elsewhere in the universe under suitable conditions.

Size, Scale and Abundance of Life

The biosphere contains an extraordinary abundance of organisms. Estimates place the total number of living cells on Earth at roughly 10³⁰, with a far larger cumulative total over geological time. This is many orders of magnitude greater than the estimated number of stars or Earth-like planets in the observable universe, though still vastly smaller than the number of atoms in that universe.
Life inhabits environments spanning extreme temperature, pressure and chemical conditions. Birds are known to fly at remarkable altitudes, while deep-sea organisms inhabit trenches several kilometres below sea level. Microbial life has been found within hot springs, deep subsurface rocks, Antarctic ice sheets and the deepest parts of the oceans. Some thermophilic microorganisms thrive near the upper temperature limits compatible with biomolecular stability, indicating that temperature, rather than depth alone, governs the ultimate boundary of the biosphere.
The subsurface biosphere—particularly microbial communities in soils, sediments and crustal rocks—contains a substantial proportion of global biomass. Estimates place prokaryotic carbon stocks in the range of hundreds of billions of tonnes, exceeding surface biomass in many regions.

Spatial Extent and Environmental Variation

The physical thickness of the biosphere is challenging to define due to the broad range of environments in which life persists. At the upper boundary, microorganisms have been detected high in the atmosphere, while deep lithospheric microbes inhabit rock layers several kilometres beneath the land surface and seabed.
On land, the biosphere is organised into biomes characterised by climate, vegetation and associated fauna. Biomes range from equatorial rainforests with high biodiversity to polar deserts with sparse life. Biome distribution is strongly influenced by latitude, while altitude, moisture availability and temperature patterns shape local ecological communities. Organisms in cold regions often exhibit adaptations such as migration, hibernation, insulation and cooperative social structures to cope with seasonal extremes.

Artificial and Experimental Biospheres

Researchers have constructed closed ecological systems to investigate self-sustaining life processes and assess the feasibility of supporting living organisms beyond Earth. These artificial biospheres, which simulate aspects of Earth’s ecological balance, allow exploration of nutrient cycling, atmospheric regulation and habitat maintenance in controlled environments. Such experiments hold relevance for astrobiology and long-duration space missions, where stable life-support systems would be essential.

Integration of Earth Systems

The biosphere interacts continuously with Earth’s physical components. Biological activity shapes atmospheric composition, influences soil development and mediates the cycling of nutrients such as carbon, nitrogen and phosphorus. Marine photosynthetic organisms contribute significantly to global oxygen production, while terrestrial vegetation affects climate through evapotranspiration and carbon storage.