From 1947 until the end of the 1950's, physicists discovered many new particles. (There were dozens of them.) The various types of particles needed a new theory to explain their strange properties.
In 1960, Murray Gell-Mann and Yuval Ne'man independently proposed a method for classifying all the particles then known. The method became known as the Eightfold Way. What the periodic table did for the elements, the Eightfold Way did for the particles. In 1964 Gell-Mann went further and proposed the existence of a new level of elementary particles called the quarks. He thought that there were three types of quarks and called them up, down, and strange. From1974 thru 1984 the theory predicted three more quarks called charm, bottom (or beauty), and top (or truth). And each quark has their corresponding anti-quark. The theory of the quark explains the existence of several particles including the nucleus of the atom. In fact the proton and neutron are each made up of three kinds of quarks and the force which holds the quarks together are made up particles called gluons.
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