The continents are vast stretches of land surrounded by water, and they represent about one-third of the planet’s surface. Each one has very different characteristics (area, relief features, inland seas, etc.), and even different boundaries, depending on who is measuring them. Generally, geographers consider only the part of the landmass that is not underwater, while geologists include the coastal margins: the continental shelves that extend under the sea and end with steep slopes beyond which the oceanic basins start.
Today, we divide Earth’s landmasses into seven continents: Europe, Asia, Africa, North America, South America, Oceania and Antarctica. Although Antarctica is the onlyI continent without permanent human habitation, it is larger than Europe and Australia! For historical and ethnological reasons, geographers have divided Europe and Asia, which in reality form one large continent, called Eurasia.
Over time, many factors (plate tectonics, volcanism, erosion, sedimentation, etc.) have transformed Earth’s relief features and its continents. In spite of their differences, the continents all have older, more stable parts and younger, more active ones. They also all have a similar underlying structure. Each rests on a shield of bedrock dating from the Precambrian Period, around which are sedimentary basins and mountain ranges that are old (rounded peaks, located near the shield) or recent (scarped, near the coasts). The shield, or platform, contains the oldest geologic layers and is generally located in the interior of continents. The sedimentary basins, located in adjoining zones, are depressions in which sediments have accumulated.