1. FOUR CONDITIONS FOR LIFE QUESTIONS 1
FOUR CONDITIONS FOR LIFE QUESTIONS 1. Why can’t other planets in the solar system support human life?
The eight other planets cannot support life because they are either too hot or too cold, their surfaces are bombarded by lethal radiation, or they lack the water or gases capable of supporting life.

2. 2. Identify and describe the four conditions or requirements needed to support life.
There is a constant and relatively mild temperature.
There is an abundance of water
There is sufficient quantity of the gases, such as oxygen, nitrogen, and carbon dioxide, that are necessary for sustaining life
There is an atmosphere of sufficient thickness to protect living things from the sun’s ultraviolet radiation.

3. 3. Why is Earth referred to as a “fragile miracle”?
Because these four important conditions exist in such an intricate and perfectly balanced combination that it seems unlikely that the same combination could be duplicated anywhere else.

4. 4. Explain the statement: “To a large extent, these life sustaining conditions depend on the special planetary position and other characteristics of the Earth itself.”
These conditions depend on Earth’s distance from the sun, its rotation on its axis and revolution around the sun, and its gravitational and magnetic fields.

5. 5. What is the Greenhouse effect?
This is carbon dioxide (CO2) and water vapour (H2O) combined in the atmosphere.

6. 6. What role does plant cover play in stabilizing Earth’s temperature?
Plant cover plays a major role in stabilizing the average temperature. It does this in two ways, through photosynthesis and by decreasing the “reflectivity” effect or albedo of Earth’s surface.

7. 7. Explain in detail the importance of water.
Biologists think that life probably began in the world’s oceans; water is not only essential to living things, but is actually a major component of them. The human body is made up of 70% water; water is also the solution in which metabolic, or energy-producing reactions take place in organisms and by which waste products are transported from them.

8. 8. How did Earth’s early atmosphere most likely develop?
Earth’s early atmosphere likely developed as a result of vapours expelled by volcanic activity. It most likely consisted of methane, ammonia, carbon dioxide and water vapour. Ultraviolet radiation broke down this early atmosphere so that it evolved into one that was chiefly nitrogen, carbon dioxide, and water vapour.

9. 9. List and explain why the gases of our present atmosphere are essential for maintaining life on Earth.
The building blocks of carbo hydrates, fats and proteins which are essential for maintaining life on Earth come from the compounds of oxygen, nitrogen and carbon.

10. 10. Describe what the Earth’s atmosphere looks like.
The Earth’s atmosphere is a gaseous layer of a relatively unique thickness. The layer of gases varies from 80 to 100 km in thickness, which is actually very thin if we compare it to the total circumference of the Earth.

11. 11. In addition to maintaining an even and stable surface temperature, what else does the Earth’s atmosphere do?
It also shields Earth from collision with harmful cosmic particles such as meteors. On falling to Earth most meteors are consumed through friction with the atmosphere.

12. 12. What would happen if the Earth’s oxygen level were to raise or drop?
If the quantity of oxygen dipped below 21%, animal life could not survive; but if oxygen exceeded 25% of the atmosphere, most plant life would be destroyed through spontaneous combustion.