The Origin of the Continents

Abstract

DR. R. H. RASTALL'S interesting article in NATURE of May 2, p. 646, raises what is perhaps the most difficult problem or group of problems that geophysicists have yet to solve. In considering the origin of the continents, the essential points to be explained are the restriction of the continental blocks to little more than one-third of the earth's surface and the marked asymmetry of their distribution. The formerly popular “tetrahedral” hypothesis, apart from its descriptive inadequacy, has hitherto failed hopelessly when confronted with the principle of isostasy. It clearly implies a process of lateral differentiation whereby the earth's store of granite could become strongly concentrated at the corners and along the edges of the alleged tetrahedron, leaving the interior of the faces, corresponding to the oceanic areas, substantially free from granite. Otherwise the tetrahedral form would be unstable and therefore temporary. No one, however, has succeeded in devising any workable process arising out of the earth's contraction which would lead to such lateral concentration of the continental rocks.