Quarks are believed to be one of the basic building blocks of matter. Quarks were first discovered in experiments done at the Stanford Linear Accelerator Center in the late 1960's and early 1970's.
Three families of quarks are known to exist. Each family contains two quarks. The first family consists of Up and Down quarks, the quarks that join together to form protons and neutrons. The second family consists of Strange and Charm quarks and only exist at high energies. The third family consists of Top and Bottom quarks and only exist at very high energies. The Top quark was finally discovered in 1995 at the Fermi National Accelerator Laboratory.