Because of Thunderstorms

The earth's electrical field is maintained by thunderstorms - 1,000 to 2,000 thunderstorms are continually active across the earth. Since the earth's surface is highly conductive, this electrical charge is evenly and rapidly dispersed acroos the earth. Standing barefoot on the earth (or otherwise connecting to the earth) connects the human body with the unlimited supply of free electrons resident in and on the surface of the earth. The whole circuit is referred to as the global electrical circuit. It is estimated that this current would disappear in less than an hour if all thunderstorm activity ceased. Standing barefoot on the earth also connects the human body with rhythmic cycles of the earth's energy field. These are essential for synchronizing biological clocks, hormonal cycles anf physiological rhythms.