Usually, nearby islands are also considered to be part of a continent. Japan, for example, is part of the continent of Asia. Greenland and all the islands in the Caribbean Sea are usually considered part of North America. Only a very small number of islands are not considered part of any continent.

Europe and Asia are actually part of a single, enormous piece of land called Eurasia. However, geographers historically have treated them as two separate continents because their societies developed somewhat separately.

Riding the Tectonic Plates

Our Earth is made up of three main layers. The core is in the center. The mantle wraps around the core. The outer crust is like Earth's skin.

The crust and the top part of the mantle form a hard, stiff shell around Earth. This shell is broken into huge sections called tectonic plates. These plates slide around on the mantle, which is made of superhot melted rock. For hundreds of millions of years, tectonic plates have been slowly sliding around the surface of Earth. They are still sliding today. Scientists believe their constant motion formed the continents.

The continents first began to form nearly 4 billion years ago, soon after Earth formed. At that time, a huge ocean covered Earth. Only a small part of the crust was made of land. Scientists believe this material built up along the edges of tectonic plates. It was made of rock that rose to the surface when plates crashed into each other.

Some of this rock formed into small islands above the surface of the ocean. Over time, these islands grew bigger. When plates carrying islands crashed into each other, the islands did not sink back into the mantle. Instead, the separate islands fused together into larger landmasses. Over time, these landmasses became the first continents.

The Supercontinent Starts to Break Apart

Millions of years ago, Earth looked very different. The continents were not where they are today. About 480 million years ago, most continents were scattered chunks of land lying along or below the Equator. Millions of years of constant tectonic activity slowly changed their positions. By 240 million years ago, almost all the world's land was joined in a single supercontinent.

About 200 million years ago, the supercontinent began to break apart. The separate pieces then slowly moved away from each other. These were the beginnings of the continents we know today.

One giant landmass that split off would later become Europe, Asia and North America. Antarctica and Australia also broke away and drifted south. At the time, they were still joined together. The small piece of land that would become India broke away too. For millions of years, it moved north as a large island, until it finally ran into Asia. Slowly, the different landmasses moved to their present locations.

The positions of the continents are always changing. North America and Europe are moving away from each other by about an inch a year. The continents are also continuing to break apart. In time, part of California will likely separate from North America and become an island.

Changing Face of Earth

The surface of the continents has changed many times. Great mountain ranges have risen and then been worn away. Ocean waters have flooded huge areas and then slowly dried up. Huge ice sheets have come and gone. They shaped the land as they advanced and then melted away.

On every continent, mountains continue to form. One way mountains form is through the crashing together of two tectonic plates. The force of the crash creates wrinkles in the crust, just as a rug wrinkles when you push against it. These "wrinkles" are what we call mountains.

Asia's Himalaya mountain range was formed that way several million years ago. They rose as the plate carrying India pushed against the plate carrying Asia. That pushing is still happening. As a result, the Himalayas grows taller every year.

North America

North America is the third-largest continent. It stretches from the Aleutian Islands in the northwest to the Isthmus of Panama in the south.

The western part of the continent is full of young mountains. Among them are the Rockies, North America's largest mountain chain. Older mountain ranges rise near the East Coast of the United States and Canada.

North America has a bigger range of climates than any other continent. Its Arctic regions are extremely cold. Yet, tropical jungles can also be found on the continent in Central America. Animals that live in North America include bison (Bison bison), moose (Alces alces) and the California condor (Gymnogyps californianus) in the north, and llamas (Lama glama), vipers and tapirs in the south.

The United States, Canada, Mexico, Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panama are all countries in North America. Greenland is also geographically part of North America, even though Denmark partly controls it.

European colonizers have destroyed many of the groups living in North America. Still, more than 500 Indigenous nations have survived and continued their traditions. These nations include the Inuit of Arctic Canada and Alaska, the Iroquois of the United States and the Nahua of Mexico.

People have migrated to North America for thousands of years. This migration continues today. Since the United States became a country, more than 86 million people have moved there.

South America

South America is connected to North America by the narrow Isthmus of Panama. The two continents were not always connected. They came together only 3 million years ago.

South America is the fourth-largest continent. It stretches from the sunny beaches of the Caribbean Sea to icy waters near the Antarctic Circle.

The Andes is the longest mountain range on any continent. It runs the entire length of South America.

The Amazon River in northern South America is the largest river in the world. It flows through the world's largest tropical rainforest. More than 15,000 kinds of plants and animals are found only in the Amazon Basin, including the Amazon River dolphin (Inia geoffrensis) and the blue-throated macaw (Ara glaucogularis).

Twelve countries are located in South America. South America was largely colonized by Spain and Portugal. This destroyed many Indigenous cultures. However, some Indigenous nations, like the Guarani in Brazil, continue their traditional ways of life.

Europe

Europe is the sixth-largest continent. It contains just 7% of the world's land. Europe is only slightly larger than Canada. However, its population is more than twice that of South America. Europe has more than 40 countries. It also has many of the world's best-known cities.

The Ural Mountains separate Europe from Asia. Two nations are in both continents. These are Russia and Kazakhstan.

Europe's most famous mountain range is the Alps. It stretches across eight countries.

Europeans colonized land on every continent except Antarctica. They gained wealth from the natural resources from those countries. This did not help the Indigenous people. It often destroyed their cultures and led to weaker governments and less wealth. This difference in wealth continues to this day.

Human development harmed animal life in Europe. Many animals were driven to extinction or close to extinction. Some of the animals that have survived are the Eurasian lynx (Lynx lynx), the Golden eagle (Aquila chrysaetos) and Mediterranean tortoises (Testudo graeca).

Africa

Africa is the second-largest continent. It covers an area more than three times that of the United States. From north to south, Africa stretches about 8,000 kilometers (5,000 miles). It is connected to Asia by the Isthmus of Suez in Egypt.

The Sahara Desert covers much of North Africa. It is the world's largest hot desert. The world's longest river, the Nile, is also in Africa. It flows more than 6,600 kilometers (4,100 miles).

The top half of Africa is mostly dry, hot desert. The middle area has savannas, or flat, grassy plains. This region is home to lions (Panthera leo), giraffes, elephants and many other wild animals. The central and southern areas of Africa are full of rainforests.

Africa also has mountainous areas. The peak of Tanzania's Mount Kilimanjaro is covered by snow all year long.

The continent of Africa is slowly splitting in two. In time, land containing four African countries will break off from the rest of the continent. Those countries are Eritrea, Ethiopia, Djibouti and Somalia.

Africa is home to 56 countries, yet it accounts for only 18,3% of the world's population. During colonization, more than 12.5 million Africans were kidnapped, enslaved, and taken to colonies in the Americas. Nearly all of Africa was colonized by Europe. In the mid-20th century, African leaders broke free of this rule. However, Indigenous groups still had to fight for their rights. The Maasai in Tanzania are fighting for land. It is being taken away from them to use for farming and game reserves. They raise cattle as part of their traditional culture and need the land for grazing.

Asia

Asia is the largest continent. It stretches from the eastern Mediterranean Sea to the western Pacific Ocean. About 60 percent of Earth's population lives in Asia. More than a third of the world's people live in China and India alone. Asia has the world’s highest population of Indigenous people of any continent. But some groups, like the Hmong of Southeast Asia, have faced many years of unfair and harmful treatment.

The continent of Asia includes many islands. Some of them are countries. The Philippines, Indonesia, Japan and Taiwan are major island nations in Asia.

Altogether, there are more than 40 countries in Asia. They have some of the world’s most desired natural resources, like oil. European countries used colonization to take these resources. Today, foreign powers compete to continue to have access to them.

Asia has many different climate regions. They range from polar in the Siberian Arctic to tropical in equatorial Indonesia. Parts of central Asia, including the Gobi Desert, are dry year-round. Many different animals live in these climates, including the King cobra, Asian elephant (Elephas maximus) and Oriental scops owl (Otus sonia).

Asia is the most mountainous continent. More than 50 of the highest peaks in the world are in Asia. Mount Everest, which is in Nepal and China, is the highest point on Earth at more than 8,700 meters (29,000 feet) high.

Australia and Oceania

Oceania is the name for thousands of islands that sit in the Pacific Ocean. It includes Australia, which is the smallest continent in the world but the largest part of Oceania.

There are two other major landmasses of Oceania. One is Zealandia, which includes the country of New Zealand. Much of Zealandia is formed by rocks that are underwater. The other large land area in Oceania is the island of New Guinea. It contains the country of Papua New Guinea.

Oceania also includes three areas made up of only islands. These areas are Melanesia, Micronesia and Polynesia, which includes the U.S. state of Hawai‘i.

Australia and Oceania has the second-smallest human population of any continent, after Antarctica. Fewer than 40 million people live there, mostly in coastal cities. The Aboriginal and the Torres Strait Islander are the two major Indigenous groups. Both have resisted colonial and modern influence. They continue their traditional practices.

Australia and Oceania is full of unusual animals. When the continent broke away from Antarctica more than 60 million years ago, it carried a cargo of animals with it. These animals developed into creatures found only in Australia, such as the koala (Phascolarctos cinereus), the platypus (Ornithorhynchus anatinus) and the Tasmanian devil (Sarcophilus harrisii).

Antarctica

Antarctica is the windiest and iciest place on Earth. It is larger than Europe and Australia, but it has no permanent human population. The only people there are visiting scientists. They live among penguins, albatrosses, seals and other animals. These animals depend on the sea to survive.

The climate of Antarctica makes normal human life impossible. Temperatures drop to -73 degrees Celsius (-100 degrees Fahrenheit). The continent is almost completely covered with ice. This ice can be as much as 3.2 kilometers (2 miles) deep.

Antarctica does not have any countries.