Continent (geology)
On Old Earth, or on Gaian style worlds exhibiting similar patterns of plate tectonics, a large platform of metamorphic rock and largely granitic igneous rock, covered over much of its area by relatively thin layers of sedimentary rocks. The margin of a continent is defined by either the continental shelf, and a drop off to an adjacent basaltic ocean basin, or a junction with another continent. The continent may or may not consist of land; indeed for much of Old Earth's prehistory history the continents had extensive shallow epicontinental seas. Examples of Old Earth continents include Eurasia and its offshore islands, Australia and its offshore islands such as New Guinea and Tasmania, South America, Africa, India prior to its merger with Eurasia, and past continents such as Gondwana, Laurasia, and Pangea. A small continent that lacks a craton of older rocks may be called a microcontinent; Madagascar, and Zealandia (including New Zealand and New Caledonia) or the Mascarene or Kerguelen plateaus and their associated islands are examples.

Gaian worlds of sufficient age may have full continents in the same sense as the continents of Old Earth geology, or if it is early in their history they may have only microcontinents. These may be continents from the geologist's point of view without being a continent in the usual geographic sense. For instance, on To'ul'h Prime the continents do exist as distinct areas of higher land, but they are not separated by a world-ocean as on Old Earth, and on Pacifica the water level is high enough to conceal the outlines of the underlying continents from casual observation. A case less extreme than Pacifica's is Chorus, which rather resembles the Old Earth of the late Mesozoic in that the geological continents are half-submerged. Terraformers often aim for something similar to the distribution of land and water seen on Old Earth when humanity arose, with results such as those seen on Arcadia or Corona. Smaller bodies such as Arean and Selenian worlds, terraformed or otherwise, lack continents in the geologist's sense, though if they are terraformed and water is added the resulting bodies of land may be referred to as continents by local mapmakers. In a few cases artificial Gaian gardenworld planets have been constructed, complete with underlying plate tectonics and continental platforms; such worlds have continents in sense geologists use. Some of the better known examples of this are found at Ao Lai and Ecotopia.
 
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    The slow movement of crustal plates (usually bearing continents or terranes) on a tectonically active eoarean, eogaian, or gaian world. The plates float over the molten asthenosphere.
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    A stable, ancient region, usually flat to slightly convex, in a continent on a world that experiences continental drift; the core from which the continent has grown over time.
 
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Development Notes
Text by Stephen Inniss

Initially published on 20 June 2010.