C13. The Earth's Atmosphere (Y11 - Spring 2)

Question 1

🟢 Gases and their Percentage in the Earth’s atmosphere today

Answer 1

1. Nitrogen, N2 - 78%
2. Oxygen, O2 - 21%
3. Argon, Ar - 0.9%
4. Carbon Dioxide, O2 - 0.04%
5. Water Vapour & Group 0, H2O, Ne - Traces

Question 2

🟢 Gases in the Earth’s atmosphere in the billion years of Earth

Answer 2

1. Carbon Dioxide, CO2
2. Water Vapour, H2O
3. Nitrogen, N2
4. Ammonia, NH3
5. Methane, CH4

Question 3

🟢 What was the Earth like 4.6 billion years ago

Answer 3

It was a molten ball of rock and minerals

Question 4

🟢 Explain how the levels of oxygen in our atmosphere increased and include any relevant chemical equations.

Answer 4

Algae and green plants, which performed photosynthesis released oxygen into the atmosphere.

6CO2 + 6H2O (light) —> (light) C6H12O6 + 6O2

Carbon Dioxide + Water —-> Glucose + Oxygen

Question 5

🟢 Explain how most of the CO2 in Earth’s ealy atmosphere was removed to arrive at the level of around 0.04% today

Answer 5

Water vapour condensed, forming oceans, which ghe CO2 dissolved in. Algae and green plants evolved, which perfomed photosynthesis, which involved plants absorbing CO2 from the atmosphere.

6CO2 + 6H2O (light) —> (light) C6H12O6 + 6O2

Finally, dead organisms died, and were buried under sediment, forming fossils which went to form coal reserves.

Question 6

🟢 Explain the origin of Nitrogen gas in the early atmosphere

Answer 6

Through the reaction of oxygen and ammonia

Question 7

🟢 Suggest why the percentage of N2 of the composition of air remains so high

Answer 7

They may’ve been no reactions to diminish the level of nitrogen.

Question 8

🟢 Give a chemical equation for the formulation of N2 from ammonia, NH3

Answer 8

4NH3 + 3O2 —> 6H2O + 2N2

Question 9

🟢 Up until 100 years ago and for the previous 200 million years, the amount of CO2 ​in the atmosphere had remained unchanged.

Describe the natural processes by which plants and marine life remove carbon dioxide from the atmosphere (6 marks)

Answer 9

One way carbon dioxide has been removed from the atmosphere via natural processes is through algae and green plants. Plants take in carbon dioxide during photosynthesis. This is then converted to glucose and oxygen in plants. CO2 dissolves in seawater and produces carbonates. Carbonates are jsed by marine animals to make shells and bones. Then when they die, sedimentry rock or limestone are also formed to form remains of dead marine life.

Question 10

🟢 The levels of carbon dioxide in the atmosphere have increased continually / over the last one hundred years.

Suggest t​wo r​easons for this increase (2 marks)

Answer 10

One reason may be that fossil fuels have been burned, releasing carbon from some of the natural carbon stores found in the oceans. Humans have also cut down trees, releasing the carbon that was stored in them too.

Question 11

🟢 The theories about how Earth’s atmosphere has developed have evolved and changed over time.

Suggest o​ne​reason for this and explain why (2 marks)

Answer 11

One reason for this is due to the fact that technology has improved and developed over time, allowing us to gather more information about what the atmosphere could’ve been made up of millions and billions of years ago (like analysis of rocks, ice core, and e.c.t). This increase information allowed for other theories to be disproved as well.

Question 12

🟢 Aside from water vapour, what two main gases account for approximately 99% of the atmosphere

Answer 12

Nitrogen and Oxygen

Question 13

🟢 Scientists now believe that over three billion years ago, Earth’s atmosphere consisted of a mixture of water vapour, carbon dioxide, methane and ammonia.

The mixture has changed significantly since then.

Suggest two reasons for the decrease in water vapour and two for the decrease in carbon dioxide (4 marks)

Answer 13

One reason is due to the fact that the water vapour condensed as the earth formed to form and another reason is water, and water vapour is used by plants in photosynthesis to form glucose and oxygen.

One reason form carbon dioxide being reduced is due to it being needed for photosynthesis, and the other reason is that it dissolved in the oceans.

Question 14

🟢 Describe how the gases in Earth’s early atmosphere (in the first billion years) formed (3 marks)

Answer 14

In the first billion years of earth’s existence, there was high volcanic activity that produced carbon dioxide, methane, water vapour, and ammonia, and methane, which formed the early earth’s atmosphere.

Question 15

🟢 What was the Earth’s atmosphere like before the first billion years and to which planets was it similar?

Answer 15

The early atmosphere was mainly carbin dioxide, with no oxygen or other gases at all. You can say that it was similar to Mars and Venus.

Question 16

🟢 The percentages of N2 ​and O2 ​in the Earth’s atmosphere of millions of years ago have changed.

Describe how the amounts of these gases have been changed a​nd​suggest what caused this change.

Answer 16

Oxygen has increases, due to plants and vegetation producing oxygen in photosynthesis, along with glucose.

Also, the nitrogen has increased, due to the reaction of ammonia (from volcanoes) with oxygen, as well as the action of bacteria and microorganisms.

Question 17

🟢 What type of organism was first responsible for producing oxygen on Earth and when did this occur? (2 marks)

Answer 17

Algae was the first responsibke organism for producing oxygen on earth, as it was the first green plant that photosynthesised. This happened around 2.7 billion years ago.

Question 18

🟢 Equation for Photosynthesis

Answer 18

6CO2 + 6H2O (light) —> (light) C6H12O6 + 6O2

Question 19

🟢 Explain how deposits of limestone, coal and crude oil are formed

Answer 19

Plants, plankton, and marine life die and fall to the seabed (which released the carbon compounds they contained). Over millions of years they become buried in sediment and are compressed to form sedimentry rock such as limestone as well as fossil fuels.

Question 20

🟢 Describe and explain how the atmosphere of the early Earth has changed to the atmosphere that we know today.

Answer 20

Main Changes:

• Oxygen increased because plants and algae developed and used carbon diozide, producing oxygen, and decreasing the level of carbon dioxide
• Carbon dioxide also decreased because oceans formed and dissolved carbon dioxide
• Carbon dioxide became locked up in sedimentry/carbonate rocks and fossil fuels
• Oceans formed because the water vapour condensed
• Continents formed because the Earth cooled, forming a supercontinent called Pangea which formed the separate continents
• Volcanoes reduced because the Earth cooled forming a crust.

Other Changes:

• Nitrogen has formed because ammonia in the Earth’s early atmosphere
• Activity of dentrifing bacteria produces nitrogen gas from nitrate compounds in soil.