How did the oceans first form?
Oxygen and hydrogen in the air reacted to form water
Early plants released water during photosynthesis
Carbon dioxide dissolved in falling rainwater
Water vapour condensed as the Earth cooled
97 exam-style questions on Edexcel GCSE Chemistry 9.2 Earth and atmospheric science, covering 9.2.1 The Earth's early atmosphere, 9.2.2 How the atmosphere evolved, 9.2.3 Chemical test for oxygen, and 9.2.4 The greenhouse effect and climate change. Each one has a worked solution and a mark scheme showing where the marks go.