Topsoil, the uppermost of the three major soil horizons. This layer and the humus that lies above it house all the organic content in soil.
Oxygen-breathing.
Non-oxygen-breathing.
Earth's atmosphere is a blanket of gases that includes nitrogen (78%), oxygen (21%), argon (0.93%), and a combination of water vapor, carbon dioxide, ozone, and noble gases such as neon (0.07%). Most of these gases are con tained in the troposphere, the lowest layer, which extends to about 10 mi. (16 km) above the planet's surface.
Subsoil, beneath topsoil and above the C horizon. Though the B horizon contains no organic material, its presence is critical if the soil is to be suit able for sustaining a varied ecosystem.
The changes that particular elements undergo as they pass back and forth through the various earth systems (e.g., the biosphere) and particularly between living and non-living matter. The elements involved in biogeochemical cycles are hydrogen, oxygen, carbon, nitrogen, phosphorus, and sulfur.
A combination of all living things on Earth—plants, animals, birds, marine life, insects, viruses, single-cell organisms, and so on—as well as all formerly living things that have not yet decomposed.
The bottommost of the soil horizons, between subsoil and bedrock. The C horizon is made of regolith, or weathered rock.
The upper portion or layer of the trees in a forest. A forest with a closed canopy is one so dense with vegeta tion that the sky is not visible from the ground.
The pattern of weather conditions in a particular region over an extended period. Compare with weather.
A system that per mits the exchange of energy with its external environment but does not allow matter to pass between the environment and the system. Compare with isolated system on the one hand and open system on the other.
A substance made up of atoms, chemically bonded to one another, of more than one chemical element.
Organisms that obtain their energy from the chemical breakdown of dead organisms as well as from animal and plant waste products. The principal forms of decomposer are bacteria and fungi.
A chemical reaction in which a compound is broken down into simpler compounds, or into its constituent elements. In the bios phere, this often is achieved through the help of detritivores and decomposers.
Organisms that feed on waste matter, breaking organic material down into inorganic substances that then can become available to the biosphere in the form of nutrients for plants. Their function is similar to that of decomposers; however, unlike decomposers—which tend to be bacteria or fungi—detritivores are relatively complex organisms, such as earthworms or maggots.
The study of the relation ships between organisms and their environments.
A community of inter dependent organisms along with the in organic components of their environment.
A substance made up of only one kind of atom. Unlike compounds, elements cannot be broken down chemically into other substances.
A state of heightened biological productivity in a body of water, which is typically detrimental to the ecosystem in which it takes place. Eutrophication can be caused by an excess of nitrogen or phosphorus, in the form of nitrates and phosphates, respectively.
The process whereby liquid water is converted into a gaseous state and transported to the atmosphere. When discussing the atmosphere and precipitation, usually evaporation is distinguished from transpiration. In this context, evaporation refers solely to the transfer of water from nonliving sources, such as the soil or the surface of a lake.
The loss of water to the atmosphere via the combined (and related) processes of evaporation and transpiration.
A term describing the interaction of plants, herbivores, carnivores, omnivores, decomposers, and detritivores in an ecosystem. Each of these organisms consumes nutrients and passes it along to other organisms. Earth scientists typically prefer this name to food chain, an everyday term for a similar phenomenon. A food chain is a series of singular organisms in which each plant or animal depends on the organism that precedes it. Food chains rarely exist in nature.
The upper part of Earth's continental crust, or that portion of the solid earth on which human beings live and which provides them with most of their food and natural resources.
Unincorporated, often par tially decomposed plant residue that lies at the top of soil and eventually will decay fully to become part of it.
Any organic chemical compound whose molecules are made up of nothing but carbon and hydrogen atoms.
The continuous circulation of water throughout Earth and between various earth systems.
The entirety of Earth's water, excluding water vapor in the atmosphere but including all oceans, lakes, streams, groundwater, snow, and ice.
A system that is separated so fully from the rest of the uni verse that it exchanges neither matter nor energy with its environment. This is an imaginary construct, since full isolation is impossible.
The removal of soil mate rials that are in solution, or dissolved in water.
A naturally occurring, typically inorganic substance with a specific chemical composition and a crystalline structure. A crystalline structure is one in which the constituent parts have a simple and definite geometric arrangement that is repeated in all directions.
A system that allows complete, or near complete, exchange of matter and energy with its environment.
At one time, chemists used the term organic only in reference to living things. Now the word is applied to most compounds containing carbon, with the exception of carbonates (which are miner als) and oxides, such as carbon dioxide.
A disease-carrying para site, usually a microorganism.
The biological conversion of light energy (that is, electro magnetic energy) from the Sun to chemical energy in plants.
Capable of being dissolved.
Any set of interactions that can be set apart mentally from the rest of the universe for the purposes of study, observation, and measurement.
The condition of the atmosphere at a given time and place. Compare with climate.
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