Introduction
Spheres, Scales, Systems and Cycles
OVERVIEW
The aim of this chapter is to introduce you to the subject of
physical geography and to show that it is relevant to a wide range
of important environmental issues. This chapter also presents
the concept of systems: a framework for studying the earth's environmental
processes that is used throughout the book.
-
Physical Geography is the study of the earth's surface
and of how and why it changes. Its focus is the life
layer:
the shallow surface layer where lands and oceans meet the atmosphere
and where most forms of life are found.
- Processes affecting the earth's surface operate in four
realms: the atmosphere, the lithosphere, the
hydrosphere and the biosphere.
- The four realms and their processes can be studied at global,
through continental and regional, to local scales.
- The processes of the four realms interact in the life layer
to produce the environments of the earth's surface.
- A helpful way to understand the processes that shape the environments
of the life layer is to study them as systems.
- Most natural systems are flow systems in which material
(matter flow systems) or energy (energy flow systems)
flows along pathways interconnected in a structure.
- All flow systems have a power source.
-
Open flow systems have inputs and outputs, while closed
flow systems do not.
-
Cycles are closed matter flow systems. In a cycle,
a fixed amount of material is continually recirculated through
a series of pathways or loops.
-
Feedback in a flow system occurs when the flow in one
pathway affects the flow in another. Positive feedback
increases flow while negative feedback reduces it.
- Negative feedback in a flow system tends to produce stability
or equilibrium.
-
Time cycles are periodic changes in system flow rates
that occur over periods ranging from hours to millions of years.
- Studying the systems of the life layer and their interactions
leads to a better understanding of the human habitat, environmental
problems and global change.
KEY TERMS
physical systems open flow system
geography flow system closed flow
life layer pathways system
atmosphere structure cycle
lithosphere input material cycle
hydrosphere output feedback
biosphere power source equilibrium
human habitat time cycle
STUDY QUESTIONS
1. What is physical geography and what is its main object or focus
of study?
2. Name and define the four great realms of the earth.
3. What is a flow system and what are its key components?
4. What is the difference between an open and a closed flow system?
A matter and an energy flow system?
5. Give an example of a cycle that might be studied in physical
geography and describe its operation in system terms.
6. Describe the concepts of feedback and equilibrium as they apply
to systems. Illustrate your answer with an example of a natural
system.
7. What is a time cycle as applied to a system? Give an example
of a time cycle in a natural system.
8. Discuss the value of systems thinking for natural scientists.
Go to this chapter's quiz
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