In the UK, Paul Devereux and Andrew York mapped out areas of UFO activity in Leicestershire, comparing them with maps of tectonic strain along geological fault lines. Two years later Michael Persinger and Gyslaine Lafrenière carried out a similar comparison of the US. Both teams found striking correlations between areas of active tectonic pressure and accounts of unusual lights in the sky.

One of the mechanisms suggested by Persinger and Lafrenière to account for the lights was a form of piezo-electrical effect. This occurs when crystals are crushed under pressure, producing electricity and sometimes ionising the air above to create glowing lights. These might be considered supernatural or extraterrestrial.

These lights are assumed to be plasmas - gases in which some of the atoms have become ions and sometimes called the "fourth state" of matter. Such airborne plasmas glow brightly at night and appear silvery and metallic during the day - just like flying saucers.

One of the mysteries about these plasmas is that they have been described as behaving "intelligently". Intelligent gases have been the subject of only the most far-out science fiction, but research by Mircea Sanduloviciu at Romania's Cuza University has suggested that life may, indeed, be a gas...