Oxygen Cycle

Oxygen cycle image The Oxygen cycle is not described in most textbooks but is nevertheless very important for the living world. Oxygen (O₂) is the byproduct of photosynthesis in plants and a reactant of cellular respiration in both plants and animals. Oxygen is the second major component of the atmosphere after nitrogen gas (N₂) and composes approximately 21 percent of the atmosphere.

Oxygen is a reactive molecule. Besides involvement in the photosynthetic and cellular respiration reactions, oxygen is removed from the atmosphere during the weathering process of rock and minerals. As new rocks and minerals are exposed to the atmosphere during weathering, oxygen combines with them in a process called oxidation and is, thus, removed from the atmosphere.

Oxygen is also important in the formation of atmospheric ozone. Sunlight breaks water (H₂O) vapor into hydrogen gas and oxygen, and the hydrogen escapes Earth's atmosphere and travels into outer space. Ozone (O₃) is a naturally occurring reaction product in the atmosphere, where it forms a layer. The ozone layer is important for filtering out much of the harmful ultraviolet (UV) radiation from the sun and keeping it from hitting the Earth.

The chemical reaction for the formation of ozone is:

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