The early atmosphere of Earth was very different from the atmosphere we have today. Some scientists believe Earth's early atmosphere was similar to the atmosphere of Mars today.
The table below shows the approximate percentages of carbon dioxide and oxygen in the atmospheres of Mars and Earth today:
GasPercentage (%) in Mars’ atmospherePercentage (%) in Earth’s atmosphere todayCarbon dioxide95.320.04Oxygen0.1320.95 \begin{array}{|l|c|c|} \hline \textbf{Gas} & \textbf{Percentage (\%) in Mars' atmosphere} & \textbf{Percentage (\%) in Earth's atmosphere today} \\\hline \text{Carbon dioxide} & 95.32 & 0.04 \\\hline \text{Oxygen} & 0.13 & 20.95 \\\hline \end{array} GasCarbon dioxideOxygenPercentage (%) in Mars’ atmosphere95.320.13Percentage (%) in Earth’s atmosphere today0.0420.95Describe and explain the processes that caused the percentage of carbon dioxide in Earth's atmosphere to decrease from its early level to the level today.
Explain how the development of early photosynthetic organisms changed the percentage of oxygen in the atmosphere.
Give one reason why scientists are not certain about the exact percentage of each gas in Earth's early atmosphere.
7 exam-style questions on AQA GCSE Chemistry 9.1 The composition and evolution of the Earth's atmosphere, covering 9.1.1 The proportions of different gases in the atmosphere, 9.1.2 The Earth's early atmosphere, 9.1.3 How oxygen increased, and 9.1.4 How carbon dioxide decreased. Each one has a worked solution and a mark scheme showing where the marks go.