The light-dependent reactions of photosynthesis are responsible for liberating oxygen. Within chloroplasts, light energy drives the splitting of water molecules. This process, known as photolysis, provides the electrons needed for the electron transport chain, ultimately generating ATP and NADPH, which power the subsequent light-independent reactions (Calvin cycle). Oxygen is a byproduct of this water-splitting process.
This liberation of oxygen is fundamental to life on Earth as we know it. It formed the oxygen-rich atmosphere that enabled the evolution of aerobic respiration, a far more efficient energy-producing process than anaerobic alternatives. This evolutionary step paved the way for the development of complex multicellular organisms. Furthermore, the continuous replenishment of atmospheric oxygen sustains the respiration of countless organisms globally.
