The Earth consists of a mantle some 2885 km thick surrounding a core of radius 3485 km. The existence of the core was inferred from seismic observation as early as 1897; refraction of seismic P waves by the core creates a “shadow zone” at distances between 105° and 140° from the epicenter. Further analysis of seismic waves has shown that the core is divided into a liquid outer core about 2260 km thick surrounding a solid inner core of radius 1225 km. During the past decade there has been a shift from descriptive studies of the Earth's deep interior to serious attempts to relate the structures deduced within the Earth to the processes that may cause or result from them.
The Earth acts as a great engine that converts thermal and potential energy into mechanical and magnetic energy. This engine operates as two separate convective systems in the mantle and core. Motions in the fluid outer core produce the magnetic field of the Earth by dynamo action. The energy supply for these motions is...
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