1. The Four Conditions for Life

2. What unique conditions make Earth the only planet in the solar system capable of sustaining life?
#1: There is a constant and relatively mild TEMPERATURE.
#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.

3. The Four Spheres Scientists divide regions on Earth into four spheres, or areas of activity.
Lithosphere:
made up of Earth’s crust and all the materials – soil, rocks and minerals-that form the crust
Atmosphere:
Composed of all the gases in the air

4. Hydrosphere:
Consists of all the water on Earth
Biosphere:
All life, from simplest bacterium to complex human beings

5. 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 effect.
The greenhouse effect is a good thing, without it the Earth would become too cold for life to exist.
However, man’s activities appear to be altering the natural balance.

6. The Greenhouse Effect