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Mineralogists have been able to use the pressure and temperature data from the seismic and modelling studies alongside knowledge of the elemental composition of the Earth to reproduce these conditions in experimental settings and measure changes in crystal structure.
These studies explain the chemical changes associated with the major seismic discontinuities in the mantle and show the crystallographic structures expected in the inner core of the Earth.
When a rock crystallizes from melt (magma or lava), it is an igneous rock.
These advances led to the development of a layered model of the Earth, with a crust and lithosphere on top, the mantle below (separated within itself by seismic discontinuities at 410 and 660 kilometers), and the outer core and inner core below that.
More recently, seismologists have been able to create detailed images of wave speeds inside the earth in the same way a doctor images a body in a CT scan.
These images have led to a much more detailed view of the interior of the Earth, and have replaced the simplified layered model with a much more dynamic model.
There are three major types of rock: igneous, sedimentary, and metamorphic.
The rock cycle illustrates the relationships among them (see diagram).
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle (that is, the heat transfer caused by bulk movement of molecules within fluids).