4.9.1 The composition and evolution of the Earth's atmosphere (will come up)

Question 1

Describe the proportions of gases in the modern atmosphere

Answer 1

80% Nitrogen
20% Oxygen
Small quantities of CO2, H2O and noble gases

Question 2

Describe the Earth’s early atmosphere and how it was formed

Answer 2

The Earth was hot when it was formed
There was significant volcanic activity
Gases have been released from these volcanos including CO2 N2 CH4 NH3 H2O

When the oceans formed, carbon dioxide dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of carbon dioxide in the atmosphere. No knowledge of other theories is required.

Question 3

How did the amount of oxygen in the atmosphere increase

Answer 3

Algae and plants produced the atmospheric O2 by photosynthesis
As the amount of O2 gradually increased, there was more plants that produced more oxygen

Question 4

How did the amount of carbon dioxide in the atmosphere decrease

Answer 4

Some CO2 was dissolved in the oceans where it reacted with metal ions to form insoluble carbonates such as CaCO3 or was taken in by animals to become a part of skeleton. When animal dies, this becomes a sedimentary rock
Some CO2 was used in photosynthesis to make oxygen

Question 5

ignore

Answer 5

ignore