Composition of the lunar highlands: Possible implications for evolution of the Earth's crust

This paper is a theoretical investigation of the implications for the origin of the earth's continents and ocean basins of three possible chemical compositions for the lunar highlands: ultrabasic, basic, and intermediate to acidic. Ultrabasic or basic lunar highlands would imply that the existence of sialic crust on the earth is due to some major difference between the earth and the moon; the three most likely differences are presence of an atmosphere, presence of a core, and size. The theory that continents are essentially geosynclinal accretions is shown by recent geological investigations to have numerous weaknesses and may imply an age for the earth of over 5 b.y. A proposed alternative is that large, thick primordial continents were formed by high‐pressure magmatic processes caused by early segregation of the core, with later continental evolution being essentially subordinate accretion to and reworking of these protocontinents. A basic composition for the lunar highlands would imply that the basic crustal layers of the earth are the remnants of a primordial basaltic crust. Sialic lunar highlands would imply that the earth's continents are essentially igneous, and were derived from the mantle early in geologic time. Furthermore, the nearly global extent of the lunar highlands suggests that the earth's crust has evolved by the growth of ocean basins rather than the growth of continents, perhaps by foundering of continental segments under flood basalts as proposed by Beloussov. A geochemical probe of Venus is recommended as an approach to further study of continent formation, because the nearly identical size and density of Venus would eliminate the variables of mass and core formation complicating the earth‐moon comparison.