Editing Geophysics (section)

=== Electricity ===
Although we mainly notice electricity during [[thunderstorms]], there is always a downward electric field near the surface that averages 120 [[volt]]s per meter.<ref name=Harrison>{{harvnb|Harrison|Carslaw|2003}}</ref> Relative to the solid Earth, the ionization of the planet's atmosphere is a result of the galactic [[cosmic rays]] penetrating it, which leaves it with a net positive charge.<ref>{{Cite web |last=Nicoll |first=Keri |date=April 2016 |title=Earth's electric atmosphere |url=https://www.metlink.org/wp-content/uploads/2020/11/PhysRev25_4_Nicoll.pdf |access-date=February 18, 2024 |website=metlink.org}}</ref> A current of about 1800 [[ampere]]s flows in the global circuit.<ref name=Harrison/> It flows downward from the [[ionosphere]] over most of the Earth and back upwards through thunderstorms. The flow is manifested by lightning below the clouds and [[sprite (lightning)|sprite]]s above.

A variety of electric methods are used in geophysical survey. Some measure [[spontaneous potential]], a potential that arises in the ground because of human-made or natural disturbances. [[Telluric current]]s flow in Earth and the oceans. They have two causes: [[electromagnetic induction]] by the time-varying, external-origin [[geomagnetic field]] and motion of conducting bodies (such as seawater) across the Earth's permanent magnetic field.<ref>{{harvnb|Lanzerotti|Gregori|1986}}</ref> The distribution of telluric current density can be used to detect variations in [[electrical resistivity]] of underground structures. Geophysicists can also provide the electric current themselves (see [[induced polarization]] and [[electrical resistivity tomography]]).