Now Wait Just 9,192,631,770 Oscillations...

Man's earliest attempts at timekeeping involved creating and maintaining simple calendars for tracking the seasons. Ice Age hunters in Europe over 20,000 years ago scratched lines and gouged holes in sticks and bones, counting the days between phases of the moon. As early man's societies became more complex, so did their need to manage time. The development of sophisticated bureaucracies and religious rituals called for time to be tracked in ever-smaller increments.

In 1967 the cesium atom's natural frequency was formally recognized as the new international unit of time. The second was defined as 9,192,631,770 oscillations or cycles of the cesium atom's resonant frequency. This replaced the old second that was defined in terms of the earth's rotation.

As of 2005, an atomic clock built by the National Institute of Standards and Technology (NIST), and based on the natural resonance frequency of the cesium atom, would not be off by more than a second in over 60 million years.