During the Great Oxidation Event, approximately 2.4 billion years ago, ancestral cyanobacteria proliferated in Earth's oceans, leading to a dramatic shift in the composition of the early atmosphere.
Explain how the metabolic activity of these early microorganisms caused both a rise in atmospheric oxygen levels and a decline in carbon dioxide levels.
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.