The Evolution of Earth's Atmosphere

The Earth's atmosphere has evolved significantly over 4.6 billion years. Initially dominated by volcanic gases, it was primarily composed of carbon dioxide. As the Earth cooled, water vapor condensed to form oceans, which absorbed carbon dioxide, leading to the formation of sedimentary rocks. Photosynthesis by plants and algae further transformed the atmosphere by reducing carbon dioxide and increasing oxygen levels. Some plants became fossil fuels, storing carbon and preventing its return to the atmosphere. This process led to the current atmospheric composition of 80% nitrogen and 20% oxygen.

Explain how fossil fuels contributed to the carbon cycle in the atmosphere.

What changes occurred in the concentrations of carbon dioxide and oxygen over time?