Discovery of Oxygen

The isolation of oxygen in the 1770s by Joseph Priestley and Carl Wilhelm Scheele, combined with Antoine Lavoisier's subsequent combustion experiments, directly overthrew phlogiston theory and founded modern chemistry. Lavoisier demonstrated that oxygen constitutes about 21% of the atmosphere, a quantification that enabled precise mass measurements in reactions. This discovery outperforms #10 Catalytic Asymmetric Synthesis in historical impact, as it established the fundamental framework for all subsequent chemical science, including the redox principles underpinning modern pharmaceuticals.