The seven continents that make up the world's land mass are, from largest to smallest: Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Only 29 percent of the Earth's surface is land. The percentage area of each continent is shown here. Highest point on Earth: Mt. Everest, China/Nepal, 29,035 ft (8,850 m). Lowest point on Earth: Mariana Trench, Pacific Ocean, 35,840 ft (10,924 m). Longest river: Nile, Egypt/Sudan/Uganda, 4,187 miles. Largest lake: Caspian Sea, Azerbaijan/Iran/Turkmenistan/ Kazakhstan/Russian Federation, 146,101 sq miles (378,400 sq km). Largest ocean: Pacific Ocean, 63,804,540 sq miles (165,241,000 sq km). Africa is sometimes nicknamed the “Mother Continent” due to its being the oldest inhabited continent on Earth. Humans and human ancestors have lived in Africa for more than 5 million years. Africa, the second-largest continent, is bounded by the Mediterranean Sea, the Red Sea, the Indian Ocean, and the Atlantic Ocean. MOVING CONTINENTS THE CONTINENTS THAT MAKE UP most of the Earth's land surface are always on the move, shifted around by forces deep inside the Earth. This is known as continental drift. Movement, or drift, takes place because of intense heat generated within the Earth.The heat is carried upward where it disturbs the cool, rocky surface, or crust, forcing sections of it, called plates, to move. Each year the continents, parts of the plates, drift nearly half an inch (about a centimeter), some getting closer together, others moving farther apart, some grinding past each other. As this happens, many of the Earth's natural features are created or changed. In the beginning Scientists believe that some 300 million years ago all the land on Earth was joined together in one “supercontinent” called Pangaea. It was surrounded by a giant ocean, Panthalassa. About 200 million years ago, as the plates moved, Pangaea began to split into two great landmasses, Laurasia in the north, and Gondwanaland in the south. These were separated by the Tethys Sea. As the plates continued to move, the two landmasses split and moved farther apart, eventually forming the continents. RESTLESS EARTHBecause the Earth appears to stand still, it is difficult to imagine that the crust is moving. In fact, its plates move in three main ways – as spreading ridges, subduction zones, and transform faults, all shown on the artwork below. It is possible to see the effect this activity has had on the landscape. The Rocky Mountains in North America were formed when two plates collided, while the Great Rift Valley in Africa is the result of plates pulling apart. Volcanoes and earthquakes are also dramatic reminders that the plates are moving. SPREADING RIDGESA spreading ridge occurs where two plates start to pull apart and molten rocks from the Earth's mantle well up to fill the gap. If this happens along the ocean floor, it creates an underwater mountain chain such as the Mid-Atlantic Ridge. Sometimes the peaks of these mountains break the surface as volcanic islands, as happened with Iceland. When a spreading ridge occurs on land, it creates a…
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