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The Four Conditions for Life
What unique conditions make Earth
the only planet in the solar system
capable of sustaining life?
#1: There is a constant and relatively mild
#2: There is an abundance of WATER.
#3: There is a sufficient quantity of GASES, such
as oxygen, nitrogen and carbon dioxide that are
necessary to sustain life.
#4: There is an ATMOSPHERE of sufficient
thickness to protect all living things from the
sun’s ultraviolet rays.
The Four Spheres
Scientists divide regions on Earth into four
spheres, or areas of activity.
• made up of Earth’s
crust and all the
materials – soil, rocks
and minerals-that
form the crust
• Composed of all the
gases in the air
• Consists of all the
water on Earth
• All life, from simplest
bacterium to complex
human beings
The Greenhouse Effect
The Earth receives ultraviolet (UV) radiation from the sun,
absorbs it, and then radiates the energy out as infrared radiation
However, the Earth’s average temperature is
15 C.
The Earth is warmer because our atmosphere
traps some of the outgoing IR radiation. This
is a natural process known as the greenhouse
The greenhouse effect is a good thing, without
it the Earth would become too cold for life to
However, man’s activities appear to be
altering the natural balance.
The Greenhouse Effect