365 Days of Climate Awareness 65 - The Biosphere

The biosphere (Greek: "bios", life, and "sphaira", sphere), also known as the ecosphere, is the zone of earth in which life exists. It extends from below the ground and the sea floor up into the stratosphere, and possibly beyond. (Microorganisms have been shown in tests to survive in space.) It includes all planetary ecosystems, as well as their innumerable and complicated relationships.

Terrestrial plants and oceanic chlorophyll.

If we consider the biosphere to be a system, it is very nearly closed. The thermodynamic concept of a "system" has three types: open, where matter and energy freely enter an exit; closed, where matter is not exchanged between the system and its surroundings, but energy is; and isolated, where neither matter nor energy is exchanged across the system boundary. Earth itself is a nearly closed system, as the loss of mass through the escape of hydrogen and human space flight, and gain through asteroids, is negligible, but solar radiation both incoming and reflected are central to the existence of life on earth.

Likewise the biosphere exchanges a vanishingly small amount of matter with outer space and the earth's interior, but incoming solar energy is used worldwide. Most life in the biosphere would die off without the constant influx of solar energy. Photosynthesis is the foundation of nearly all upper ocean and terrestrial ecosystems. On the sea floor and within the earth itself chemosynthesis--archea and bacteria metabolizing chemicals from within the planet as an energy source--is another. It has been estimated that plants and algae consume 130 terawatts (one million millions) of solar energy per year. No comparable estimate for the global energy use of chemosynthetic communities exists.

Major terrestrial biomes.  Larger version

Within the concept of the biosphere are several other large-scale concepts for analyzing the presence of life on the planet. One is biomass, the total mass of all living organisms within a given ecosystem. The earth's total biomass has been estimated at 550 Gt C (gigatons of carbon). The term biomass is also applied to localized ecosystems and classes of organisms. Another concept is that of the biome, a group of flora and fauna occupying a specific habitat. (Biomes can range from global extent to a terrarium or the intestine of a vertebrate.) Like the biosphere, a biome can be considered a system, but is almost always open, with regular exchange of mass and energy across the biome's spatial boundaries.

Tomorrow: tropical rainforests.

Be well!