The paper by Heinrich D. Holland provides a comprehensive overview of the oxygenation history of the Earth's atmosphere and oceans over the last 3.85 billion years. The Earth's history is divided into five stages, each characterized by distinct changes in atmospheric and oceanic oxygen levels. - **Stage 1 (3.85–2.45 Ga)**: The atmosphere and oceans were largely anoxic, with possible exceptions in shallow ocean oxygen oases. - **Stage 2 (2.45–1.85 Ga)**: Atmospheric oxygen levels rose to 0.02–0.04 atm, while shallow oceans became mildly oxygenated, and deep oceans remained anoxic. - **Stage 3 (1.85–0.85 Ga)**: Atmospheric oxygen levels remained stable, and most surface and deep oceans were mildly oxygenated. - **Stage 4 (0.85–0.54 Ga)**: Atmospheric oxygen levels increased to values not much less than 0.2 atm, with shallow oceans becoming oxygenated and deep oceans remaining anoxic during intense Neoproterozoic ice ages. - **Stage 5 (0.54 Ga–present)**: Atmospheric oxygen levels likely peaked at around 0.3 atm during the Carboniferous, with shallow oceans remaining oxygenated and deep oceans fluctuating. The paper discusses the evidence for these changes, including mass-independent fractionation of sulfur isotopes, carbon isotopic data, and the presence or absence of marine manganese deposits and phosphorite deposits. It also explores the mechanisms behind the major transitions in oxygenation, such as the Great Oxidation Event (GOE) and the development of the 'Canfield Ocean' during the Mesoproterozoic. The author emphasizes the complexity of the processes involved and the need for further research to fully understand the oxygenation history of the Earth.The paper by Heinrich D. Holland provides a comprehensive overview of the oxygenation history of the Earth's atmosphere and oceans over the last 3.85 billion years. The Earth's history is divided into five stages, each characterized by distinct changes in atmospheric and oceanic oxygen levels. - **Stage 1 (3.85–2.45 Ga)**: The atmosphere and oceans were largely anoxic, with possible exceptions in shallow ocean oxygen oases. - **Stage 2 (2.45–1.85 Ga)**: Atmospheric oxygen levels rose to 0.02–0.04 atm, while shallow oceans became mildly oxygenated, and deep oceans remained anoxic. - **Stage 3 (1.85–0.85 Ga)**: Atmospheric oxygen levels remained stable, and most surface and deep oceans were mildly oxygenated. - **Stage 4 (0.85–0.54 Ga)**: Atmospheric oxygen levels increased to values not much less than 0.2 atm, with shallow oceans becoming oxygenated and deep oceans remaining anoxic during intense Neoproterozoic ice ages. - **Stage 5 (0.54 Ga–present)**: Atmospheric oxygen levels likely peaked at around 0.3 atm during the Carboniferous, with shallow oceans remaining oxygenated and deep oceans fluctuating. The paper discusses the evidence for these changes, including mass-independent fractionation of sulfur isotopes, carbon isotopic data, and the presence or absence of marine manganese deposits and phosphorite deposits. It also explores the mechanisms behind the major transitions in oxygenation, such as the Great Oxidation Event (GOE) and the development of the 'Canfield Ocean' during the Mesoproterozoic. The author emphasizes the complexity of the processes involved and the need for further research to fully understand the oxygenation history of the Earth.