When was time invented?

Time was not invented in the conventional sense, which requires someone or something to create it. As far as scientists are aware, as of 2014, time has existed as long as the universe. Whether time, as humans perceive it, existed before then is unknown.

Time is generally considered a fourth dimension and a basis for determining the order in which activities take place in the past, present or future. It can also be used to determine the duration of events and the time between them. Scientists are unsure about the precise nature and definition of time. The first known instruments used to measure time were sundials and water clocks.