While we're chattering and grinding away, the Earth makes its own 'music' as a result of numerous natural phenomenona. Even though they are not audible to the human ear, they are around us all the time. The source of most of the VLF emissions is lightning. Lightning strikes emit a broadband pulse of radio waves, just as they unleash a visible flash of light. When heard via a radio, thses signals from nearby lightning sound like bacon frying, or the crackle of a fire.
Space scientists call the sounds 'sferics', which comes from atmospherics.
Even when there is no lightning in a particular area, VLF crackles in from thousands of kilometres away. Some of these sferics even manage to travel around the Earth. Radio waves can move such long distances by bouncing back and forth between our planet's surface and the ionosphere - a layer of the atmosphere ionised by solar ultraviolet radiation. Gallagher and his colleagues have set up VLF radio, which broadcasts the sounds of the Earth, via the Internet 24 hours a day. Sferics that travel very far through the waveguide become 'tweeks', which produce a musical ricochet sound in the loudspeaker of the receiver.