The discovery of SEOP took decades for all the pieces to fall into place to create a complete technique. First, in 1897, Zeeman's studies of sodium vapor led to the first result of optical pumping. The next piece was found in 1950 when Kastler determined a method to electronically spin-polarize rubidium alkali metal vapor using an applied magnetic field and illuminating the vapor with resonant circularly polarized light. Ten years later, Marie-Anne Bouchiat, T. M. Carver, and C. M. Varnum performed spin exchange, in which the electronic spin polarization was transferred to nuclear spins of a noble gas (He and Xe) through gas-phased collisions. Since then, this method has been greatly improved and expanded to use with other noble gases and alkali metals.