ABSTRACT
All life on earth has evolved in these fields. Defining them in physical terms permits direct comparison with far stronger man-made fields that have come to dominate all civilized environments in the past century. Energy in the oscillating natural fields is almost entirely in the extremely low frequency (ELF) spectrum, with peaks at frequencies between 8 and 32 Hz, the Schumann resonances (1). Their electric components are around 0.01 V/m, with magnetic fields of 1-10 nT. These natural oscillations are ducted worldwide between the earth’s surface and the ionosphere at an approximate height of 250 km. With a circumference of 41,000 km, the earth may act as a cavity resonator for this ducted propagation (at the velocity of light, 300,000 km/s), behaving resonantly at a frequency around 8Hz. Neither solar nor terrestrial sources contribute significant amounts of radiofrequency or microwave energy to the earth’s biosphere, and we may
*Portions of this chapter were first published in D.Clements-Croome, ed. Electromagnetic Environments and Safety in Buildings, London: Spon Press, 2002.
