The Great Oxidation Event (GOE) refers to a major period in Earth's history when the Earth's atmosphere began to accumulate free oxygen ($\text{O}_2$) in massive quantities. This atmospheric shift occurred over hundreds of millions of years, fundamentally altering planetary geochemistry and biochemistry. Prior to this event, the atmosphere was largely anoxic, meaning it lacked significant free oxygen. The rise of oxygen is widely attributed to the widespread metabolic activities of early photosynthetic organisms, which released oxygen as a byproduct of converting energy from sunlight. The increased oxygen levels had profound global consequences, leading to the oxidation of dissolved iron in the oceans and resulting in a significant change in global nutrient cycling, which helped pave the way for the diversification of complex aerobic life forms.