Earth has seven main pieces of land. These are known as continents. From largest to smallest, they are Asia, Africa, North America, South America, Antarctica, Europe, and Australia.

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, most geographers treat them as two separate continents because their societies developed somewhat separately.

Riding the Tectonic Plates

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 up into huge sections called tectonic plates. These plates slide around on the mantle, which is made up of super-hot 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 four billion years ago, soon after Earth, itself, formed. At that time, a huge ocean covered Earth. Only a small part of the crust was made up 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.

Pangaea 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 south of the Equator. Millions of years of constant tectonic activity slowly changed their positions. By 240 million years ago, almost all of the world's land was joined in a single, huge continent. Scientists call this supercontinent Pangaea.

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

One giant landmass that split off from Pangaea 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 2.5 centimeters (one 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 Himalayas were 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 grow 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.

People sometimes mistakenly think the U.S. and Canada are the only countries in North America. In fact, this is not true at all. Mexico, Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama are all also in North America. Greenland is also geographically part of North America, even though Denmark partly controls it.

South America

South America is connected to North America by the narrow Isthmus of Panama. The two continents weren't always connected. They came together only three 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 River basin.

Twelve countries are located in South America.

Europe

Europe is the sixth-largest continent. It contains just seven percent 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 major 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.

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 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 6,560 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, 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 14 percent of the world's population.

Asia

Asia is the largest continent. It stretches from the eastern Mediterranean Sea to the western Pacific Ocean. Sixty percent of Earth's population lives in Asia. More than a third of the world's people live in China and India alone.

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

Altogether, there are more than 40 countries in Asia.

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.

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

Australia/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/Oceania has the second-smallest human population of any continent, after Antarctica. Fewer than 40 million people live there, mostly in coastal cities.

Australia/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, the platypus, and the Tasmanian devil.

Antarctica

Antarctica is the windiest and iciest place on Earth. It is larger than Europe or Australia, but has no permanent human population. The only people there are visiting scientists.

The climate of Antarctica makes normal human life impossible. Temperatures drop to lower than 73 degrees Celsius (100 degrees Farenheit) below zero. The continent is almost completely covered with ice. This ice can be as much as 3.2 kilometers (two miles) deep.

Antarctica does not have any countries.