Continents are large landmasses formed over millions of years through volcanic activity and orogeny events. The seven continents are Australia, Europe, Antarctica, South America, North America, Africa, and Asia. The continents drift on the mantle, and the supercontinent cycle predicts that they will come together again in the future. The rock that makes up continents is much older than the ocean floor between them.
A continent is a large landmass defined by convention. There are currently seven on Earth, which are as follows, in order of size: Australia, Europe, Antarctica, South America, North America, Africa and Asia. All are inhabited, although Antarctica only has a population of around 4,000 during the summer and 1,000 during the winter. According to the most recent estimates, the population of Australia is approximately 22.6 million; Europe, 739 million; South America, 387.4 million; North America, 528.7 million; Africa, 1 billion; and Asia, 4.1 billion. The total world population exceeds 6.9 billion.
Continents were formed over hundreds of millions of years through so-called orogeny (“rock birth”) events, in which a volcanic hotspot spews hundreds of thousands of cubic kilometers of lava, which cools to create a craton, a large layer of rock. The fringes of cratons tend to be flooded, creating a continental shelf, which plunges abruptly into the deep sea. The area they cover varies 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 level was about 230 feet (70 meters) higher. Just 10,000 years ago, during the last ice age, when ice sheets covered much of the Northern Hemisphere, the seas were about 120 meters lower, opening up areas of land such as the North Sea, Flores Strait and Bering Strait .
The continents drift on the underlying mantle, which is made of superheated rock with a plastic texture. Over geologic time, these land masses shift, break apart, and reform in something called the supercontinent cycle. This is a cycle in which the earth alternately merges into a giant supercontinent and breaks up into fragments. The last supercontinent, Pangea, existed about 250 million years ago. Within the next 250 million years, the continents are predicted to come together again into one gigantic mass that has been called Pangea Ultima.
The rock that makes up these land masses is much older than the ocean floor between them. That’s because oceanic crust is constantly being pulled into areas known as subduction zones, where the crust melts and flows back to the mantle. In areas in the center of the oceans known as rift valleys, magma rises up from the mantle, creating new land. So the ocean floor is only 50-100 million years old, while the earth’s crust may be 4 billion years old.
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