A continent is a large landmass defined by convention. There are currently seven continents on the Earth, in order of size: Australia, Europe, Antarctica, South America, North America, Africa, and Asia. All of the continents are inhabited, but Antarctica only has a population of about 4,000 during the summer, 1,000 during the winter. As of 2008, the population of Australia is roughly 20 million; Europe, 700 million; South America, 370 million; North America, 520 million; Africa, 900 million; Asia, 3.9 billion. The total world population is over 6.7 billion.

Continents are formed over the course of hundreds of millions of years through so-called orogeny ("rock birth") events, where a volcanic hotspot pours out hundreds of thousands of cubic kilometers of lava, which cools to create a craton, a large layer of rock making up the continent. The fringes of cratons tend to be flooded, creating a continental shelf, which drops off abruptly into the deep sea. The area of the continents vary over geological time, as the Earth's ice sheets melt and refreeze. More than 40 million years ago, there were barely any ice sheets on the planet, and the world's sea levels were approximately 70 meters (230 ft) higher. Just 10,000 years ago, during the last Ice Age, when ice sheets covered much of the Northern Hemisphere, the seas were about 35 m (120 ft) shallower, opening up areas of land such as the North Sea, the Flores Strait, and Bering Strait.

Continents drift on the mantle below, made of superheated rock with a plastic texture. Over geologic time, continents move, breaking apart and reforming in something called the supercontinent cycle. This is a cycle whereby continents alternatively merge together into one giant supercontinent and break apart into fragments. The last supercontinent, Pangaea, existed about 250 million years ago. Within the next 250 million years, the continents are expected to come together again into a supercontinent that has been named Pangaea Ultima.

The rock making up the continents is much older than the ocean floor between them. This is because the oceanic crust is constantly being drawn beneath the continents into areas known as subduction zones, where the crust melts and returns to the mantle. In areas in the center of oceans known as rift valleys, magma comes up from the mantle, creating new land. So the ocean crust is only 50-100 million years old, while the continental crust may be as old as 4 billion years.