The main component of the Earth's atmosphere that supports combustion is oxygen. This diatomic molecule makes up approximately 21% of the atmosphere and is essential for various combustion reactions. In the presence of a fuel and an ignition source, oxygen reacts chemically to produce heat and light, resulting in a flame. The availability of oxygen is crucial for supporting life, enabling cellular respiration in organisms. Additionally, understanding the role of oxygen in combustion is important for fields like fire safety, engineering, and environmental science.