Continental margins and the extent and number of the continents

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Abstract
A new map of the extent of continental crust shows that the continents are more extensive and less dispersed than they are conventionally thought to be. Their total area is 210.4 × 106 km², or 41% of the earth's surface, and there are 14 of them. Continent‐ocean contacts are mapped on the basis of a literature survey, and continent‐continent contacts are drawn along plate boundaries; thus although Eurasia is still the largest continent, it does not include the separate continents India and Arabia and surrenders northeastern Siberia to North America. Much of the Arctic Ocean is underlain by North American continental crust, and North America is the second‐largest continent. Central America and New Zealand are recognized as continents, the latter being nine‐tenths submerged, and there are four microcontinents: Rockall, Seychelles, Agulhas, and Jan Mayen. Several oceanic windows, enclaves within the continents, must be recognized if the extent of the continents is to be accurately delineated. The average thickness of continental crust is 36 km; small continents seem to be thinner than large ones, and height and thickness are strongly interdependent. The total volume of continental crust is 7.2 × 109 km³, somewhat less than the 8.0 × 109 km³ estimate of Ronov and Yaroshevskiy (1977). Mean heights are significantly lower than the 875 m commonly quoted from Kossinna (1933), because submerged parts of the continents (30.6% of their total area) are correctly accounted for; the new estimate of mean height is ∼120 m. The relationship between mean height and area for individual continents, however, is still observed. Modal heights are not correlated with area and are ∼ 250 m for most of the large continents. Certain continents have anomalous mean or modal heights, suggesting that the mean height‐area relationship arises from greater relative lengths of orogenic belts around and internal tectonism within larger continents; anomalous modal heights suggest anomalous epeirogenic activity. These results may have implications for the hypsometry of ancient continents: in particular, Pangea need not have had a modal height much different from that observed today.