9. Chemistry of the Atmosphere

Question 1

Name the gases and the proportions of each gas in the atmosphere today

Answer 1

• Around 4/5 of the atmosphere (approximately 80%) is nitrogen
• Around 1/5 of the atmosphere (approximately 20%) is oxygen
• There are also small proportions of other gases, including carbon dioxide, water vapour and noble gases

Question 2

How long have the proportions of gases in the atmosphere been stable for?

Answer 2

For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today

Question 3

When was the Earth formed?

Answer 3

The Earth was formed 4.6 billion years ago

Question 4

Why is evidence for the early atmosphere of the Earth limited?

Answer 4

Evidence for the early atmosphere of the Earth is limited because it happened 4.6 billion years ago

Question 5

Explain the main theory for the atmosphere of the Earth

Answer 5

• During the first billion years of the Earth’s existence there was intense volcanic activity
• This volcanic activity released the gases that formed the early atmosphere
• The water vapour in the atmosphere condensed as the Earth cooled down to form the oceans
• Volcanic activity releases large amount of CO2, so the atmosphere then would have been similar to Mars & Venus today - consisting mainly of carbon dioxide with little or no oxygen gas

Question 6

What other gases were released by volcanoes

Answer 6

• Nitrogen which gradually built up in the atmosphere
• Small amounts of methane and ammonia

Question 7

Compare the Earth’s early atmosphere with today’s atmosphere

Answer 7

There is more nitrogen, more oxygen, less carbon dioxide

Question 8

Explain how the oceans interacted with carbon dioxide from the Earth’s early atmosphere

Answer 8

When the oceans formed, carbon dioxide dissolved in the water and carbonates were precipitated, later forming sediments on seabeds, reducing the amount of carbon dioxide in the atmosphere

Recheck topic

Question 9

How did the oxygen in the atmosphere increase?

Answer 9

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

Question 10

When did algae first produce oxygen?

Answer 10

2.7 billion years ago

Question 11

What happened over the billions of years after algae first produced oxygen?

Answer 11

Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve

Question 12

How did the carbon dioxide in the atmosphere dencrease?

Answer 12

• 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 13

How are fossil fuels formed?

Answer 13

Fossil fuels are formed over millions of years from the remains of living things

Question 14

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