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Yang Xuexiang\ \ Chen Zhen\ \ Liu Suqin\ \ Song Xiuhuan\ \ Chen Dianyou(Changchun University of Earth Sciences, Changchun, 130026)  
Differential rotation of the earth′s inner core is due to the Coriolis effect. Coriolis force makes the rising material deviated westwards and results in the rotational retardation of outer materials of the earth; moreover, it also makes the decending materials deviated eastwards and results in the acceleration of inner materials of the earth. Thus, the vertical movement of the rotational bodies can produce a large scale horizontal movement called shell differential rotation. In the ideal condition, e.g. the rising material does not exchange angular moment with decending material, when the homogeneous earth is evoluted into shelled earth by gravitational differentiation, the rotation speed of the inner core increased to 27 times than that of the original, the outer core to 3 times than that of the original. However, the speed of the lower mantle varies little, the speed of upper mantle and crust is only 70~60 percent of the original; therefore, an obvious differential rotation state is formed. It is shown by the calculation of the authors that the energy resulted from the lowering of potential of the earth by gravitational differentiation has not completely been changed into the heat energy, a part of which changed into the rotating kinetic energy of the shell differential rotation; the rotating kinetic energy has approximately increased twice after differential rotation, and most of the rotational energy is concentrated in the core. The thermal convection can also produce the shell differential rotation. According to the analogue computation, two layers of the convection sphere body are recognized with equal volume. If the thermal convection makes the two layers completely exchange without angular momentum exchange, the velocity of inner shell is 10 times than that of outer shell and the rotating energy would increase three times than that of the original. Song X.D. and Richards P.G. have discovered the seismological evidence for differential rotation of the earth′s inner core. The inferred rotation rate is by the order of 1° per year faster than the daily rotation of the mantle and crust. For the differential rotation of the earth′s inner core, the solar radiation not only induces the inside and outside geomagnetic tail and reverse oscillation of crust and inner core, but also causes electromagnetic coupling and angular momentum exchange between the core and mantle. So, it controled the liberation of the earth′s inner energy. This is the reason why geological cycles are concerned with astronomical periods. The response of the global changes to the changes of the earth′s orbit and solar orbit provides evidence that the solar radiation plays a important part in liberation of the earth′s inner energy, and liberation of the earth′s inner energy plays a special part in global changes.
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