Continent Europe and Asia together as a single continent, dubbed "Eurasia". In this model, the world is divided into six continents, with North America and South America considered separate continents. Geologists use the term "continent" in a different manner from geographers. In geology a continent is defined by continental crust: a platform of metamorphic and igneous rock, largely of granitic composition. Some geologists restrict the term 'continent' to portions of the crust built around stable Precambrian "shield", typically 1.5 to 3.8 billion years old, called a craton. The craton itself is an accretionary complex of ancient mobile belts (mountain belts) from
Continent cases, there is no complete separation of these landmasses by water (disregarding the Suez Canal and Panama Canal, which are both narrow and shallow, as well as being artificial). Both these isthmuses are very narrow compared to the bulk of the landmasses they unite. North America and South America are treated as separate continents in the seven-continent model. However, they may also be viewed as a single continent known as America or the Americas. This viewpoint was common in the United States until World War II, and remains prevalent in some Asian six-continent models. This remains the more common vision