Fire is the rapid oxidation of a fuel in the exothermic process of combustion, releasing heat, light, and reaction products—its visible flames, composed mainly of carbon dioxide and water vapor, can even become ionized plasma at extreme temperatures. Ecologically, fire stimulates plant growth and maintains balance, but it also causes hazards, pollution, and soil erosion, and it releases nitrogen into the atmosphere, reducing soil fertility unless replenished by nitrogen-fixing plants like clover or peas. As one of the four classical elements, fire has been harnessed by humans for cooking, heat, agriculture, warfare, and cremation, while modern safety measures like smoke detectors, sprinklers, and professional firefighters help mitigate its dangers. The word "fire" derives from Old English fȳr and Proto-Indo-European péh2wr, and the fossil record shows wildfires first appeared 420 million years ago in the Late Silurian, following the rise of land plants 470 million years ago that boosted atmospheric oxygen. Human control of fire enabled survival in colder climates, protection from predators, and dietary changes, marking a pivotal shift in history.