Fig. 7.27. Methods for determining the Earth's paleoradius. (a) The paleomeridian method of Egyed (1960). Cross-section through the Earth with two sampling sites S, and S2 lying on a paleomeridian separated by distance d. If their paleolatitudes are >., and /.2, the ancient radius /?a is determined from (7.1.13). (b) The minimum dispersion method of Ward (1963). The positions of rock units (X„, <j>„) are transformed to a new co-ordinate system using the center of the continent as the pole (center of diagram). As the radius of the Earth is varied the latitudes of the rock units (X„) will change to some new value (>.„') but the longitudes (4>„) will remain unchanged. For any trial paleoradius, new values (/.„') can be determined and the dispersion of paleomagnetic poles recalculated. After McElhinny (1973a, 1978).
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