GCSE Chemistry 09 — Earth and Atmospheric Science

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Topics include Composition of the Modern Atmosphere, Earth's Early Atmosphere, Evolution of the Atmosphere: Oceans and Carbon Removal, Evolution of the Atmosphere: Oxygen and Life, The Greenhouse Effect, Climate Change: Evidence and Impacts, Carbon Footprint and Mitigation, and Combustion Pollutants: CO, CO2, and Particulates.

Chemistry EN

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Composition of the Modern Atmosphere

The Earth's atmosphere has been stable for approximately 200 million years, consisting mainly of nitrogen and oxygen.

Key points

Nitrogen ( $N_2$ ): ~78%
Oxygen ( $O_2$ ): ~21%
Argon (Ar): ~0.9% (most abundant noble gas)
Carbon dioxide ( $CO_2$ ): ~0.04% (trace gas)
Water vapour: Variable (0–4%) depending on temperature and humidity

Worked example

Question

The concentration of carbon dioxide in the atmosphere is approximately 0.04%. Convert this percentage into parts per million (ppm).

Solution

1. Recall the definition of 'percent' means per 100.
2. Recall that 'ppm' means per 1,000,000.
3. The factor difference is

1,000,000 \div 100 = 10,000

.
4. Calculation:

0.04 \times 10,000 = 400

.
5. Answer: 400 ppm.

Common pitfalls

Confusing the abundance of Argon (~1%) with Carbon Dioxide (~0.04%). Argon is much more abundant.
Thinking water vapour percentages are fixed; they vary significantly with weather.

Prerequisites

Understanding percentages and ratios
Chemical formulae of simple gases

Further resources

The Atmosphere
Overview of atmospheric composition.

BBC Bitesize · article