Carbon cycle
All of the processes (photosynthesis, decomposition, and respiration) by which the element carbon in its different compounds circulates between living and non-living parts of its environment.

Climate
The weather conditions that prevail in a region.

Decomposer
An organism such as a bacteria or fungus that breaks down dead plant and animal material, returning the components to the ecosystem.

Depletion
The use of a natural resource faster than it can be replenished.

Fossil fuel
A product formed from the decay of plant or animal materials from a previous geologic time. Examples include petroleum and coal.

Lithosphere
Earth's outer layer, made of the crust and outer layer of the mantle.

Matter
Anything that takes up space and has mass.

Nitrogen cycle
The series of events where atmospheric nitrogen is converted into compounds used by organisms and released back to the atmosphere by decomposition.

Ozone layer
An upper region of the atmosphere which absorbs much of the ultraviolet radiation from the sun.