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Argon is the third-most abundant gas in the Earth's atmosphere, at 0.934% (9340 ppmv).
It is more than twice as abundant as water vapor (which averages about 4000 ppmv, but varies greatly), 23 times as abundant as carbon dioxide (400 ppmv), and more than 500 times as abundant as neon (18 ppmv).
Argon was first isolated from air in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water, and nitrogen from a sample of clean air.
They had determined that nitrogen produced from chemical compounds was 0.5% lighter than nitrogen from the atmosphere.
Argon is used in some high-temperature industrial processes where ordinarily non-reactive substances become reactive.
Argon is inexpensive, since it occurs naturally in air and is readily obtained as a byproduct of cryogenic air separation in the production of liquid oxygen and liquid nitrogen: the primary constituents of air are used on a large industrial scale.Mendeleev positioned the elements on his periodic table in order of atomic weight, but the inertness of argon suggested a placement before the reactive alkali metal.Henry Moseley later solved this problem by showing that the periodic table is actually arranged in order of atomic number (see History of the periodic table).in Earth's atmosphere, which is only 31.5 ppmv (= 9340 ppmv × 0.337%), comparable with that of neon (18.18 ppmv) on Earth and with interplanetary gasses, measured by probes.The atmospheres of Mars, Mercury and Titan (the largest moon of Saturn) contain argon, predominantly as is the reason the standard atomic weight of terrestrial argon is greater than that of the next element, potassium, a fact that was puzzling when argon was discovered.Argon is produced industrially by the fractional distillation of liquid air in a cryogenic air separation unit; a process that separates liquid nitrogen, which boils at 77.3 K, from argon, which boils at 87.3 K, and liquid oxygen, which boils at 90.2 K.About 700,000 tonnes of argon are produced worldwide every year.The other noble gases (except helium) are produced this way as well, but argon is the most plentiful by far.The bulk of argon applications arise simply because it is inert and relatively cheap.Argon is the most abundant noble gas in Earth's crust, comprising 0.00015% of the crust.Nearly all of the argon in the Earth's atmosphere is radiogenic argon-40, derived from the decay of potassium-40 in the Earth's crust.