1. So…what about Earth???
As far as we know Earth is the only planet in the universe that supports life.
Scientists are looking for the reasons why there is life here.
So far they have come up with the four conditions that make life possible here. These are:
A constant and mild temperature
Abundant water in a liquid state
Thickness of the atmosphere
Ratio of CO2,, Oxygen and Nitrogen in the Atmosphere

2. 1. A constant and mild temperature
On Earth the T. range is -50 to +50 degrees C.
The constant temperature is the result of two factors:
The Greenhouse Effect
Plant Cover

3. 1a. The Greenhouse Effect
CO2 and water vapour create conditions in the atmosphere similar to a greenhouse
Light is allowed to pass through to nourish plants and warm the earth.
Heat is trapped inside to keep T. stable.
Without this the Earth’s T. would fall to -73° C.

4. 1b.Plant Cover
Photosynthesis helps control the amount of water vapour and CO2.
The dark colour of plants helps the earth absorb solar energy.

5. 2.An abundance of water in a liquid state.
70% of Earth’s surface is water
This is the same percentage of water found in the human body..
Water moves heat and nutrients throughout individual organisms (via the bloodstream) and the whole planet (via the oceans and water cycle)
Water is necessary for photosynthesis
Most scientists agree that LIFE on Earth began in the oceans.

6. Photosynthesis 6H2O + 6CO2 --energy--> C6H12O6+ 6O2 Or in English
six molecules of water plus six molecules of carbon dioxide produce one molecule of sugar plus six molecules of oxygen
This simple sugar is the basic carbohydrate that forms the basis of most of the food webs on Earth.

7. 3.Thickness of the Atmosphere
The Earth is protected by an atmosphere that varies from km thick- in comparison the protective shell of an egg is thicker.
The atmosphere
Helps maintain the temperature
Protects Earth from meteors
Ozone layer filters UV radiation which is known to cause cancer in all organisms: plant and animal.

8. 4. Atmospheric Gases GAS VENUS MARS EARTH CO2 95% 96% 0.03% Nitrogen
3.6%
78%
oxygen
trace
21%
Methane
Argon

9. These gases are essential for maintaining life on Earth.
Our basic food groups: carbohydrates, fats and proteins are all made up of combinations of carbon, oxygen, nitrogen and hydrogen.
All living organisms produce organic compounds which have one thing in common: carbon
Oxygen is produced by plants during photosynthesis and is used by animals as energy for the chemical reactions in their bodies.
Food is just chemical energy.

10. Cellular Respiration
C6H12O6 + 6O2 –energy released ----> 6CO2 + 6H2O
Or in English
One simple sugar (glucose) molecule and six oxygen molecules are broken down into six carbon dioxide molecules and six water molecules
This releases energy that organisms need to maintain life.

11. Did these conditions make life possible? OR
Important Question
Did these conditions make life possible? OR
Did life create these conditions?

12. ANSWER
Both questions seem to be true and the explanation is described by the GAIA HYPOTHESIS.