AQA GCSE Combined Science: Trilogy Chemistry Paper 2 (Foundation), 2021: Question 4
9 marks · Standard Demand difficulty · Short Answer
Analyze the evolution of Earth's atmosphere, compare it with the atmosphere of Mars, and perform a calculation based on atmospheric gas percentages.
Practise this questionQuestion
Question text
04 This question is about the atmospheres of Earth and Mars.
04.1 Earth’s early atmosphere may have been like the atmosphere of Mars today.
Why are scientists not certain about the percentage of gases in the
Earth’s early atmosphere?
[1 mark]
04.2 What was formed from the water vapour in the Earth’s early atmosphere?
[1 mark]
Tick ( ) one box.
Crude oil
Limestone
Natural gas
Oceans 17
04.3 The Earth’s atmosphere today consists mainly of nitrogen and oxygen.
Draw one line from each gas to what produced the gas.
[2 marks]
Gas What produced the gas
Algae
Animals
Nitrogen
Fossils
Oxygen
Oceans
18 Volcanoes
Table 2 shows the percentage of some gases in the atmospheres of
Earth and Mars.
Table 2
Percentage of gas in atmosphere (%)
Gas
Earth Mars
Argon 0.9 1.9
Carbon dioxide 0.04 95
Nitrogen 78 2.6
Oxygen 21 0.2
04.4 Why are animals not able to live on Mars?
[1 mark]
Tick ( ) one box.
The atmosphere of Mars does not contain enough argon.
The atmosphere of Mars does not contain enough nitrogen.
The atmosphere of Mars does not contain enough oxygen.
04.5 There is more carbon dioxide on Mars than on Earth.
Which other gas is found in larger quantities on Mars than on Earth?
[1 mark]
04.6 Calculate how many times more nitrogen than oxygen there is in the
atmosphere of Earth.
Use Table 2.
Give your answer to 2 significant figures.
[3 marks]
Number of times more nitrogen than oxygen (2 significant figures) =
Mark scheme
Show the mark scheme
AO /
Question Extra information Mark
Spec. Ref.
04.1 any one from: 1 AO1
• occurred (4.6) billion years 5.9.1.2
ago
• limited evidence
ignore nobody was there
ignore no proof
04.2 oceans 1 AO1
5.9.1.2
04.3 AO1
5.9.1.2
5.9.1.3
do not accept more than one line from a box on the left
04.4 the atmosphere of Mars does 1 AO3
not contain enough oxygen 5.9.1.3
04.5 argon allow Ar 1 AO2
5.9.1.1
78 1 AO2
12 04.6
5.9.1.1
= 3.714 do not accept a subsequent 1
step in the calculation
= 3.7 allow an answer correctly
calculated to 2 significant figures
which uses the values in the
question
Total 9
How to answer it
Earth and Mars: Evolution of the Atmosphere
What this question tests
This question assesses your knowledge of the history of the Earth's atmosphere, the processes that changed gas levels over billions of years (like photosynthesis and volcanic activity), and your ability to interpret data from a table to perform ratio calculations.
Uncertainty of the Early Atmosphere
Correct Answer
- It occurred 4.6 billion years ago.
- There is limited evidence.
Exam Technique
Avoid saying "nobody was there to see it" or "there is no proof." Examiners look for the scientific reason: the huge time scale involved means evidence has been lost or destroyed.
The Fate of Water Vapour
Correct Answer
Oceans
Key Knowledge
As the Earth cooled, water vapour in the atmosphere condensed to form the oceans. This was a major step in reducing the amount of water vapour in the air.
Sources of Atmospheric Gases
Correct Matching
- Nitrogen → Volcanoes
- Oxygen → Algae
Key Knowledge
Algae and plants produced oxygen through photosynthesis. Volcanoes released nitrogen, which gradually built up in the atmosphere because it is very unreactive.
Common Errors
Do not draw more than one line from each gas. If you draw two lines from "Nitrogen," you will lose the mark for that gas even if one of the lines is correct.
Comparing Earth and Mars
04.4 Answer
The atmosphere of Mars does not contain enough oxygen.
04.5 Answer
Argon (or Ar)
Data Reading
For 04.5, you must look at Table 2. Mars has 1.9% Argon, while Earth only has 0.9%. Even though the numbers are small, 1.9 is larger than 0.9!
Calculation: Gas Ratios
Calculate how many times more nitrogen than oxygen there is on Earth.
Step-by-Step Calculation
- Identify the values: From Table 2, Nitrogen on Earth = 78% and Oxygen on Earth = 21% .
- Set up the division: To find "how many times more," divide the larger number by the smaller number.
78 / 21 = 3.71428... - Round to Significant Figures: The question asks for 2 significant figures.
The first two digits are 3 and 7. The next digit is 1, so we round down.
Final Answer = 3.7
Significant Figures Tip
Always check the required precision. If you wrote "3.71" or "4", you would lose the final mark even if your division was correct.
Calculation Traps
Don't mix up the planets! The question specifically asks for the atmosphere of Earth. If you used the Mars values (2.6 / 0.2), your answer would be wrong.
Topics
Chemistry · C9: Chemistry of the Atmosphere
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 2 (Foundation), 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.