The Atmosphere

Question 1

For how long have the proportions of gases in the atmosphere been the same as they are today.

Answer 1

• 200 million years

Question 2

What are the proportions of gases in the atmosphere?

Answer 2

80% Nitrogen (4/5)
20% Oxygen (1/5)
Small proportions of other gases ie. CO₂, water vapour, noble gases

Question 3

Why is evidence for the Earth’s early atmosphere limited?

Answer 3

• Because it was 4.6 BILLION YEARS AGO.

Question 4

What was the Earth’s Early atmosphere likely to be similar to at the start of the intense volcanic period?

Answer 4

• Atmosphere likely to be like Mars and Venus.
• Mainly CO₂ with little to no O₂

Question 5

What gases did volcanoes release into the Early atmosphere?

Answer 5

• Water vapour
• Methane
• Ammonia
• Carbon dioxide
• Nitrogen

Question 6

What happened to the large amounts of water vapour that were in The Early Atmosphere?

Answer 6

• The Water Vapour condensed to form oceans

Question 7

How did the proportion of CO₂ in the atmosphere decrease by CO₂ dissolving in oceans ?

1st way

Answer 7

• CO₂ dissolved into the oceans.
• CO₂ + H₂O –> H₂CO₃
• H₂CO₃ –> H⁺ + CO₃²⁻
  Carbonate ions react with minerals in the ocean –> Then precipitated into sediments.
• Reduced amount of CO₂ in atmosphere.

Question 8

How did the proportion of CO₂ in the atmosphere decrease from the formation of limestone?

2nd way

Answer 8

• CO₂ used by marine organisms to make corals and shells –> made of Calcium carbonate.
• Shells compressed by dirt to form sedimentry rock, limestone.
• This reduced CO₂ in the atmosphere.

Question 9

Which living things produced the oxygen that is now in our atmosphere?
And… by what process?

Answer 9

• Algae and plants
• Photosynthesis

Question 10

What is the equation for photosynthesis?

Answer 10

6CO₂ + 6H₂O –> C₆H₁₂O₆ + 6O₂

Question 11

When did algae ( from the oceans) first produce oxygen?

Answer 11

• 2.7 billion years ago
• Oxygen appeared in the atmosphere.

Question 12

What happened after algae evolved in the oceans?

Answer 12

• Oxygen appeared in atmosphere.
• Over next billion years, plants evolved. Percentage of oxygen gradually increased to a level that enabled animals to evolve.

Question 13

What are the 2 ways the percentage of CO₂ in atmosphere decreased?

Answer 13

1.) Algae and plants = photosynthesis.
2.) Formation of sedimentary rocks and fossil fuels that contain carbon.

Question 14

Why did N₂ build up in the atmosphere?

Answer 14

N₂ built up because it is very uncreactive.

Question 15

Q.)

Describe how carbon dioxide is released into the atmosphere.
- From carbonate rocks by gelogical activity.

Answer 15

• Rocks are heated
• Carbon dioxide is released through volcanoes

Question 16

MARK SCHEME PATTERN

What are 2 additional ways nitrogen increased in the atmosphere?

Answer 16

• Released from denitrifying bacteria.
• Formed when ammonia and oxygen react.