Argon was discovered in 1894 by Lord Rayleigh and William Ramsay, who traced a small persistent discrepancy in the density of nitrogen from air to an unknown, unreactive gas mixed with it. Its name comes from the Greek argos, idle or lazy, chosen for its complete chemical inertness; it was the first of the noble gases to be found. Argon makes up nearly one per cent of the atmosphere, more than every other trace gas combined, yet had gone unnoticed precisely because it does nothing. Obtained in bulk from the distillation of liquid air, argon supplies the inert atmosphere that shields arc welding, protects growing crystals of silicon, and once filled ordinary light bulbs, and it is sealed between the panes of insulating double glazing.
Argon has an unexpected role in paleoanthropology and geology: because a small, known fraction of radioactive potassium-40 decays into argon-40 at a fixed rate, measuring the argon trapped in volcanic rock allows geologists to date it with potassium-argon and the more refined argon-argon methods, techniques that have fixed the ages of some of the most important hominin fossil sites in East Africa. The gas is also chemically almost entirely inert even by noble-gas standards, forming no confirmed stable compounds under ordinary conditions, which is why, alongside welding and lighting, it is the standard shielding atmosphere for handling reactive metals like titanium and for preserving opened bottles of wine.