AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Higher), 2020: Question 6

10 marks · Standard Demand difficulty · Extended Answer

Answer questions about carbon dioxide in the Earth's atmosphere, including the greenhouse effect, calculation of maximum carbon dioxide mass from a graph, and description of processes causing atmospheric carbon dioxide changes over geological time.

Practise this question

Question

The question page is headed 'This question is about the Earth's atmosphere' and contains three parts numbered 06.1 to 06.3 worth 1, 3 and 6 marks respectively. Part 06.1 lists four stages of the greenhouse effect: A carbon dioxide stops longer wavelength radiation escaping, B radiation is absorbed by the Earth, C longer wavelength radiation is emitted, and D shorter wavelength radiation enters the atmosphere; students must tick one of four sequence options. Figure 6 is a line graph of percentage of carbon dioxide in the Earth's atmosphere against billions of years ago from 5 to present day, showing a sharp rise to about 96%, a fall to around 50%, a later steep drop to near zero by about 2 billion years ago, and a very low value near present day. Part 06.2 asks for the maximum mass of carbon dioxide using a constant atmospheric mass of 5.15 × 10^18 kg and the graph, and part 06.3 asks for a description of the processes causing the main changes in carbon dioxide percentage over the last 4.6 billion years, with lined space for an extended written answer.
Question text

06 This question is about the Earth’s atmosphere.

06.1 Carbon dioxide is a greenhouse gas.

The greenhouse effect happens in four stages.

The four stages are:

Stage A Carbon dioxide stops longer wavelength radiation escaping

Stage B Radiation is absorbed by the Earth

Stage C Longer wavelength radiation is emitted

Stage D Shorter wavelength radiation enters the atmosphere

What is the correct order of stages A, B, C and D?

[1 mark]

Tick ( ) one box.

C, A, B, D

C, D, B, A

D, B, C, A

D, C, B, A 20

Figure 6 shows how the percentage of carbon dioxide in the Earth’s atmosphere has

changed over 4.6 billion years.

Figure 6

06.2 The mass of gas in Earth’s atmosphere remains constant at 5.15 × 1018 kg

Determine the maximum mass of carbon dioxide that was in the Earth’s atmosphere.

Use Figure 6.

[3 marks]

Mass of carbon dioxide = kg

06.3 Describe the processes that have caused the main changes in the percentage of

carbon dioxide in the Earth’s atmosphere over the last 4.6 billion years.

*20* Use Figure 6.

[6 marks]

Mark scheme

Show the mark scheme The mark scheme is a table with columns for question, answers, extra information, mark and AO/specification references. For 06.1, the correct order is D B C A for 1 mark. For 06.2, it gives a maximum percentage of 96% with allowance for 95 to 97%, then calculates 96/100 × 5.15 × 10^18 to give 4.94 × 10^18 kg, awarding marks for reading the graph, correct method and answer. For 06.3, a level-of-response mark scheme awards 4 to 6 marks for a detailed accurate account and 1 to 3 for simple stated facts; indicative content includes early increase due to volcanic activity, decreases due to ocean formation, carbon dioxide dissolving, carbonate precipitation and sedimentary rock formation, later decreases due to algae and plants photosynthesising and fossil fuel formation, and recent increase due to industrialisation, human activity and burning fossil fuels.

AO /

Question Answers Extra information Mark

Spec. Ref.

06.1 D B C A 1 AO1

5.9.2.1

06.2 (maximum % =) 96 (%) allow a value in the range 95 to 1 AO2

97 (%) 5.9.1.1

5.9.1.2

(maximum mass =) 5.9.1.4

96 18 5.9.2.2

× 5.15 × 10 allow correct use of incorrectly 1

100 determined percentage

= 4.94 × 1018 (kg) allow 4.944 × 1018 (kg) 1

AO / Spec.

Question Answers Mark

Ref.

Level 2: Scientifically relevant facts, events or processes are identified 4‒6 AO1

06.3

and given in detail to form an accurate account. 5.9.1.1

5.9.1.2

Level 1: Facts, events or processes are identified and simply stated 1‒3 5.9.1.3

but their relevance is not clear. 5.9.1.4

5.9.2.2

No relevant content 0

Indicative content:

during the first billion years of the Earth’s existence carbon dioxide

levels increased due to

• intense volcanic activity

from 4.4 to 2.7 billion years ago carbon dioxide levels decreased as

• water vapour condensed to form oceans

• carbon dioxide dissolved in the oceans

• carbonates precipitated

• sedimentary rocks formed

from 2.7 to 1.7 billion years ago carbon dioxide levels decreased as

• algae appeared

• plants evolved

• algae and plants photosynthesised

• sedimentary rocks formed

• fossil fuels formed

over the past 100-200 years carbon dioxide levels increased due to

• the industrial revolution

• human activity

• the burning of fossil fuels

Total 10

How to answer it

Earth’s Atmosphere: Carbon Dioxide Changes

What this question tests
Ordering the stages of the greenhouse effect, reading a graph to find a maximum percentage, using a percentage to calculate mass, and describing how carbon dioxide changed over Earth’s history using correct scientific processes.
Question 06: Earth’s atmosphere

Overview of the full question

💡 Key knowledge

  • Greenhouse effect stages must be in the correct sequence.
  • Percentages from graphs can be used to find masses.
  • Carbon dioxide levels changed because of volcanoes, oceans, photosynthesis, and human activity.

🧠 Exam technique

  • Use the graph carefully and read the peak value.
  • Show working for calculations to secure method marks.
  • For 6-mark descriptions, give linked processes in time order.

❌ Common errors

  • Mixing up the greenhouse effect stages.
  • Using the wrong percentage from the graph.
  • Writing vague ideas like “things changed” instead of specific processes.

Part (a) / 06.1 — Order the greenhouse effect stages

Correct order of A, B, C and D

✅ Correct answer

D, B, C, A

This matches the mark scheme exactly and scores the 1 mark.

💡 Key knowledge

  • D: Shorter wavelength radiation enters the atmosphere.
  • B: Radiation is absorbed by the Earth.
  • C: Longer wavelength radiation is emitted.
  • A: Carbon dioxide stops longer wavelength radiation escaping.

🧠 Exam technique

Think of the sequence as:

in → absorb → emit → trap

That makes the order much easier to remember in the exam.

❌ Common errors

  • Putting the “trapping” stage too early.
  • Starting with longer wavelength radiation instead of shorter wavelength radiation from the Sun.
  • Not checking the exact wording of each stage.

Part (b) / 06.2 — Maximum mass of carbon dioxide

Use Figure 6 and the total atmospheric mass

✅ Correct answer

Maximum percentage = 96%
Acceptable range: 95% to 97%

Mass of carbon dioxide = 4.94 × 10¹⁸ kg

📐 Calculations — step by step

  1. Read the highest point on the graph: 96%.
  2. Convert percentage to a decimal fraction: 96 ÷ 100 = 0.96.
  3. Multiply by the total mass of the atmosphere:

0.96 × 5.15 × 10¹⁸

= 4.944 × 10¹⁸ kg

Answer to 3 s.f. = 4.94 × 10¹⁸ kg

🧠 Exam technique

  • You can gain marks for the percentage, the method, and the final answer.
  • Keep units throughout: the final unit must be kg.
  • Use the graph value carefully; AQA allowed a small range because the peak is a little hard to read.

❌ Common calculation traps

  • Using 95% or 97% without showing graph reading carefully is usually still allowed, but the working must match.
  • Forgetting to divide by 100 before multiplying.
  • Writing 4.94 × 10¹⁸% instead of kg.
  • Rounding too early and losing accuracy.

Part (c) / 06.3 — Describe how carbon dioxide changed over 4.6 billion years

What to include for full marks

✅ What a top-level answer includes

  • Initial increase due to intense volcanic activity.
  • Decrease as the Earth cooled and water vapour condensed to form oceans.
  • Carbon dioxide dissolved in the oceans.
  • Carbonates precipitated and sedimentary rocks formed.
  • Further decrease when algae appeared and plants evolved.
  • Photosynthesis removed carbon dioxide from the atmosphere.
  • More recent increase due to the Industrial Revolution, human activity, and the burning of fossil fuels.

💡 Key knowledge

The graph shows three main patterns:

  • Early increase: volcanoes added carbon dioxide.
  • Long decrease: oceans and living things removed carbon dioxide.
  • Recent rise: humans added carbon dioxide by burning fossil fuels.

🧠 Exam technique

  • Write in the same order as the graph moves from left to right.
  • Link each change to a cause.
  • Use specific science words: dissolved, precipitated, photosynthesised, burning fossil fuels.
  • Top answers are detailed but still clear and focused.

❌ Common errors and what the examiner was looking for

  • Students often lost marks by only saying “carbon dioxide went down” without explaining why.
  • Some answers mentioned plants but forgot to say photosynthesis removes carbon dioxide.
  • Others described the graph trend but did not include the key early stage of volcanic activity.
  • To reach the top level, responses needed several correct processes linked clearly to the time periods shown.

🧠 A strong 6-mark structure

You could write it like this:

In the first billion years, carbon dioxide increased because of intense volcanic activity. Then carbon dioxide decreased as water vapour condensed to form oceans, and carbon dioxide dissolved in the oceans. Carbonates precipitated and sedimentary rocks formed, removing more carbon dioxide. Later, algae appeared and plants evolved, so photosynthesis removed carbon dioxide from the atmosphere. In the last 100–200 years, carbon dioxide has increased again because of human activity, the Industrial Revolution and burning fossil fuels.

This is the sort of answer that would reach the top level because it is detailed, accurate, and linked to the graph.

Final revision checklist

💡 Remember

  • Greenhouse effect order: D, B, C, A.
  • Maximum carbon dioxide percentage: about 96%.
  • Maximum mass: 4.94 × 10¹⁸ kg.

🧠 To score well

  • Use graph values carefully.
  • Show calculation steps.
  • Use precise scientific vocabulary.

❌ Avoid

  • Vague descriptions.
  • Wrong sequence of greenhouse effect stages.
  • Forgetting units in calculations.

Topics

Chemistry · C9: Chemistry of the Atmosphere

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Higher), 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.