A scientist produced the information in Figure 7 about the Earth's atmosphere and the Earth's average surface temperature - Edexcel - GCSE Chemistry - Question 4 - 2023 - Paper 2

To complete the bar chart, we first need to determine the total percentage of gases accounted for in the Earth's atmosphere 3 billion years ago. The gases and their percentages are:

• Carbon dioxide: 95%
• Water vapour: 4%
• All other gases: 1%

Adding these together, the total is:

$95 + 4 + 1 = 100$

Since carbon dioxide contributes 95% to the atmospheric composition, we will draw a bar reaching up to the 95% mark in the chart for carbon dioxide.