Slow but not fast global expansion may explain the surface dichotomy of Earth

Various fast and slow Earth expansion hypotheses are reviewed. Principal objectives are: 1. (1) to aid geologists to overcome their current mysticism in rejecting, accepting or sympathising with Earth expansion hypotheses without distinction; and 2. (2) to stimulate geophysicists into taking full account of the possibility that slow Earth expansion by core-mantle interaction may have occurred. Inward migration of the core-mantle boundary due to the differentiation and progressive solidification of the liquid outer core might have caused expansion of the Earth's radius at a 'slow' mean rate of 0.5 mm a^-1. A slowly expanding Earth is attractive since it could explain why two distinct types of lithosphere exist: oceanic and continental.