History

• In 1894, Sir William Ramsay and Lord Rayleigh first discovered argon by separating nitrogen from air and then argon from nitrogen, according to Chemicool, a chemistry reference site. The idea for the experiment came about as a way to determine why nitrogen-based air was heaver than nitrogen separated from a compound. In order to do this, all traces of moisture, dust and carbon dioxide were extracted from the nitrogen gas, the gas now known as argon became apparent. In effect, this newly discovered gas was found to exist in small quantities throughout the Earth's atmosphere, according to the Nobel Server.
  
  

Natural Sources

• In addition to its place in the atmosphere, argon appears in the Earth's crust at a rate of four parts per million according to Chemistry Explained. A stable atom of argon contains 22 neutrons, 18 protons and 18 electrons; however, it also exists as an isotope in three different forms--argon-36, argon-38 and argon-40. Isotopes form when extra or missing neutrons appear within the atomic structure. In total, four forms of argon exist naturally.
  
  

Radioactive Isotopes

• As a radioactive isotope, argon's atomic structure undergoes decay as excess energy, or radiation, is emitted. These isotopes are man-made and do not exist in nature. Radioactive argon is formed by bombarding the atom with a particle array. This process causes neutrons to break-off from the nucleus, which results in radioactive decay or radiation energy, according to Chemistry Explained. This energy is made up of gamma rays that carry an ionic charge. Ionic charges appear when an atom's nucleus becomes unstable.
  
  

Fractional Distillation

• Fractional distillation is a process used to produce argon, according to Chemistry Explained. As argon is found in the atmosphere, fractional distillation involves liquefying air and then heating the liquid so argon gases can be extracted. A similar process uses nitrogen, which is one of the elements argon attaches itself to. Magnesium or calcium is used to heat the nitrogen, as both elements are known to react with nitrogen. This results in leftover argon gas since the heating process doesn't affect argon.
  
  

Potassium-Argon Dating

• Potassium-argon dating is a method used within fossil dating procedures, according to the University of California-Santa Barbara. Potassium makes up an estimated 2.4 percent of the Earth's crust. Over long periods of time, potassium atoms can decay and become radioactive. As potassium atoms decay, their atomic structures lose a proton and gain a neutron. What's leftover is actually an argon atom formed by a decaying potassium atom. Fossils are dated based on how much potassium versus how much argon is present in a material.