Evolution of the Earth's Atmosphere

Question 1

state the percentages of different gases in the atmosphere

Answer 1

• around 4/5 (80%) nitrogen
• around 1/5 (20%) oxygen
• small proportions of various other gases, including carbon-dioxide, water vapour and noble gases

Question 2

explain some of the theories as to how the atmosphere evolved

Answer 2

• during the first billion years of the Earth’s existence, there was intense volcanic activity that released gases that formed the early atmosphere and water vapour that condensed to form the oceans
• at the start of this period, the Earth’s atmosphere may have been like the atmosphere of Mars and Venus today, consisting of mainly carbon-dioxide with little or no oxygen gas
• volcanoes also produced nitrogen which gradually built up in the atmosphere and there may have been small proportions of methane and ammonia
• 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

Question 3

explain how oxygen has increased in the atmosphere

Answer 3

algae and plants produced the oxygen that is now in the atmosphere by photosynthesis.

algae first produced oxygen about 2.7 billion years ago - over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve

Question 4

explain how carbon-dioxide has increased in the atmosphere

Answer 4

algae and plants decreased the percentage of carbon-dioxide in the atmosphere by photosynthesis

carbon-dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon

Question 5

state some examples of greenhouse gases

Answer 5

• water vapour
• carbon-dioxide
• methane

Question 6

describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter

Answer 6

visible light with a short wavelength is absorbed y the Earth, it is then re-radiated as longer wavelength infra red

the longer wavelength infra red cannot penetrate through the greenhouse gas layer in the atmosphere which contains carbon-dioxide and methane

Question 7

state two human activities that increase the amount of carbon-dioxide

Answer 7

• burning fossil fuels

- deforestation

Question 8

state two human activities that increase the amount of methane

Answer 8

• landfills

- farming of livestock

Question 9

describe carbon-monoxide

Answer 9

toxic gas, colourless and odourless so it is not easily detected

Question 10

describe sulfur dioxide and oxides of nitrogen

Answer 10

cause respiratory problems in humans and can cause acid rain

Question 11

describe particulates

Answer 11

can cause global dimming and health problems in humans