<P> The electrosphere layer (from tens of kilometers above the surface of the earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential . The ionosphere is the inner edge of the magnetosphere and is the part of the atmosphere that is ionized by solar radiation . (Photoionization is a physical process in which a photon is incident on an atom, ion or molecule, resulting in the ejection of one or more electrons .) </P> <P> The Earth, and almost all living things on it, are constantly bombarded by radiation from outer space . This radiation primarily consists of positively charged ions from protons to iron and larger nuclei derived sources outside our solar system . This radiation interacts with atoms in the atmosphere to create an air shower of secondary ionising radiation, including X-rays, muons, protons, alpha particles, pions, and electrons . Ionization from this secondary radiation ensures that the atmosphere is weakly conductive, and that the slight current flow from these ions over the Earth's surface balances the current flow from thunderstorms . Ions have characteristic parameters such as mobility, lifetime, and generation rate that vary with altitude . </P> <P> The potential difference between the ionosphere and the Earth is maintained by thunderstorms . In the Earth - ionosphere cavity, the electric field and conduction current in the lower atmosphere are primarily controlled by ions . </P> <P> The Schumann resonance is a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earth's electromagnetic field spectrum . Schumann resonance is due to the space between the surface of the Earth and the conductive ionosphere acting as a waveguide . The limited dimensions of the earth cause this waveguide to act as a resonant cavity for electromagnetic waves . The cavity is naturally excited by energy from lightning strikes . </P>

When were the layers of the atmosphere discovered