On March 4, 2009, the DØ and CDF collaborations both announced the discovery of the production of single top quarks via the weak interaction. This process occurs at about half the rate as the production of top quark pairs but is much more difficult to observe since it is more difficult to distinguish from background processes that can create false signals. The single top quark studies were used to measure the top quark lifetime of about 5 × 10−25 seconds, measure the last unknown element of the CKM matrix of quark inter-generational mixing, and to search for new physics beyond the Standard Model.