In 1993, professors Derr and Persinger proposed that some ignis fatuus may be geologic in origin, piezoelectrically generated under tectonic strain. The strains that move faults would also heat up the rocks, vaporizing the water in them. Rock or soil containing something piezoelectric, like quartz, silicon, or arsenic, may also produce electricity, channeled up to the surface through the soil via a column of vaporized water, there somehow appearing as earth lights. This would explain why the lights appear electrical, erratic, or even intelligent in their behavior.