Visualizing Environmental Science

The Cycling of Matter in Ecosystems 107

PROCESS DIAGRAM

Air (CO 2 )

775

Photosynthesis

by land plants

Dissolved

CO 2 in water

38,100

Burial and

compaction

to form rock

(limestone)

Erosion of

limestone

Chemical

compounds in

living organisms

Oil

Coal Natural gas

Soil

1500

Partly

decomposed

plant remains

(ancient trees)

Remains of

ancient

unicellular

marine organisms

Decomposition

(involves

respiration)

Soil

microorganism

respiration

Animal and

plant respiration

Coal

Carbon incorporated

into shells of marine

organisms

Combustion (human

and natural) of

coal, oil, natural

gas, and wood

(Total fossil fuels: 3456)

Values are from Schlesinger, W. H.

Biogeochemistry: An Analysis of Global Change

, 2nd edition.

Academic Press, San Diego (1997) and based on several sources; some values are from theU.S. Department of Energy Carbon Dioxide Information Analysis Center.

The movement of carbon between the abiotic environment (the atmosphere and ocean)
and living organisms is known as the carbon cycle. Because proteins, carbohydrates, and
other living molecules contain carbon, the process is essential to life. Sedimentary rocks
and fossil fuels hold almost all of Earth’s estimated 10^23 g of carbon. The values shown for
some of the active pools in the global carbon budget are expressed as 10^15 g of carbon.
For example, the soil contains an estimated 1500 x 10^15 g of carbon.

A manufacturing company is

considering removing a large forest. What impact, if

any, would this have on the carbon cycle? What would

be the effects, if any, if the wood from those trees were

used as fuel?

Think Critically

case study at the end of this chapter explores how global
climate change—particularly as driven by the release of
carbon dioxide from burning fossil fuels—affects the
carbon cycle.)
The thick deposits of shells of marine organisms con-
tain carbon. These shells settle to the ocean floor and are
eventually cemented together to form the sedimentary rock
limestone. The crust is dynamically active, and over millions
of years, sedimentary rock on the bottom of the seafloor

may lift to form land surfaces. The summit of Mount Ever-

est, for example, is composed of sedimentary rock.

The Hydrologic Cycle

In the hydrologic cycle water continuously circulates from

the ocean to the atmosphere to the land and back to

the ocean. It provides a renewable supply of purified wa-

ter for terrestrial organisms. This cycle results in water

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