EARTH STRUCTURE AND ORIGINS 425 Figure The magnetic field of the Earth is due to convection in the outer core, for which the configuration is not determined (re produced from D Ravat (2000) Magnetic field, origin of the Earth’s internal field In: Hancock PL and Skinner BJ (eds.) Oxford Compan ion to the Earth, pp 630 631 Oxford: Oxford University Press) Figure (A) The movement of the north magnetic pole since James Clark Ross located it in 1831 (B) The accelerating move ment of the pole at the present time, which could herald a rever sal (reproduced from McCall GJH (2003) Pole up the pole Geoscientist 13: 9, with the permission of the Geological Society Publishing House) plates, some of them immense (for example the one includes India, the Indian Ocean, Australia, and the Tasman Sea) (Figure 10) That plate movement has occurred and is occurring cannot be seriously doubted, though attempts at instrumental measurements have Figure The configuration of the ozone layer (reproduced from F Drake (2000) Ozone layer chemistry In: Hancock PL and Skinner BJ Oxford Companion to the Earth, pp 772 773 Oxford: Oxford University Press)