The Earth is subject to a continuous interaction between heat and gravitation. One result of this process is tbe occurrence of inhomogeneities in the internal density distribution of the Earth, causing a complex structure of its gravity field; an important interaction is plate tectonic movement, with seismic activities along the plate boundaries. Today, mainly because of recent advances in space technology and computer science, geodesy approaches a 10-8 relative precision in its efforts to determine the shape of the Earth and of its gravity field. It contributes very directly to modern developments in the Earth Sciences by monitoring movements, local as well as intercontinental, horizontal and vertical, steady and suddenly excited. Second, it contributes by studying the fine structure of the Earth's gravity field, and third, it measures the orientation of the Earth's body in space, thus providing insight into the global response of the Earth to the attractions of Sun and Moon.
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