The world's continents are not fixed in one place. The earth's surface is broken up into 17 tectonic plates, approximately 60 miles thick. There are 6 large ones and 11 smaller ones. They drift slowly around the world, taking oceans with them. No-one knows what makes them move, one theory is a current in the earth's mantle beneath them. The heat of the interior makes mantle bubble up toward the surface, where it cools and sinks back down again. The plates may be passengers on these currents. Another force could be ridge-push. Ocean plates, which are lower than ocean ridges, may slide downhill using the weight of the plates themselves. Another interesting theory is that due to the earth's rotation, centrifugal force contributes to the seperation of these plates.

All today's continents were once joined up in a huge supercontinent called Pangaea. Around 200 million years ago, Pangaea began to break up, and the various peices have been drifting around the world ever since. The earth's continents move around the world very slowly. They continue to move a few millimeters each year. Europe is drifting 1" (2.5cm) away from North America each week.

The east coast of South America fits neatly into the west coast of Africa. This is because they were once joined together.

There are signs of erosion by glaciers in South Africa and Australia as well as in Antartica. They were all probably joined together at the South Pole. Fossils of tropical ferns have been found on the Arctic island of Spitsbergen, indicating that the island once lay in the tropics. The site of New York was on the equator and was a dry and burning desert. Desert sands still exist in rocks below Manhattan. Striking similarities between sandstones in Brazil and western Africa have been made. Scientists have discovered all sorts of similarities across the continents, using fossils and rocks to track the movement of the continents.

As the continents drift, they sometimes collide with each other, throwing up ranges of mountains and causing earthquakes and volcanic eruptions. The Himalayas were created when India collided with Asia 40 million years ago. The deepest places on earth are the ocean trenches. The Mariana trench in the Pacific Ocean is the deepest at 1,550 miles deep, which would drown Mount Everest.

Most of the world's water is in the five great oceans, Pacific, Indian, Arctic, Southern and Atlantic, most of which are joined together by seas. Seas are not as large and are usually surround by land. The largest sea is the South China Sea, with the Caribbean Sea following close behind. Some seas are enormous lakes. The waters contain mineral salts, around 3 percent salt to water. The Dead Sea is a salt lake, so salty at 24 per cent that you can float on it. Most of the world's gold is dissolved in the sea, although it would be very difficult to gather being at 1 part gold to 400,000 million parts of water.

The Pacific Ocean is the largest water mass covering 63 million square miles. Stretching half way around the world, it contains more than half the water on earth, and contains the deepest trench. The Atlantic Ocean is the second largest, but getting wider by around 1" every year. The Indian Ocean is the third largest, and is unique amongst the oceans. It contains 28 million square miles of tropical waters, with currents which reverse direction twice a year, towards Africa in winter and India in the summer. It is rich in marine life and coral islands. The Artic Ocean is the smallest and shollowest covered by a thick sheet of ice, which never melts fully even in summer.

The earth's atmosphere is a complex sea of gases with five separate layers which gives us air and water and keeps us warm. In relation to the earth, the atmosphere is no thicker than the peel on an apple. It stretches far above the earth from the Troposphere to the Exosphere 560 miles up fading into the vacuum of space. The Troposphere which is closest to the earth, holds 75 percent of the gases and huge amounts of dust and water, and creates our weather, reaching up to 22 miles above the earth's surface. From 12 to 30 miles up, the Stratosphere containing the ozone layer which is a band of gas absorbing most of the ultraviolet rays from the sun, and holds 19 per cent of the gases, with no water vapour and is where most airliners fly due to the air being calm and clear. Temperatures range from 0C to -60C. Temperatures continue to drop the higher you climb. Above 30 to 50 miles above the earth, the Mesosphere is much too thin in gases to absorb the sun's heat and is the area where meteorites burn up as they hit these gases leaving fiery trails in the night sky. From 50 to 280 miles up, the Thermosphere has just enough gas to absorb the ultraviolet rays from the sun boosting temperatures to 2,000C, before fading into the Exosphere, and eventually the vacuum of space.

When the earth was formed, it's surface was a lake of liquid rock. As it cooled, the surface hardened into a thin crust of solid rock which floats on soft heavy mantle. The crust varies between 4 and 43 miles thick. Usually the thinner crusts are below the oceans and occasionally they split, forming volcanos. Most islands in the middle of oceans were once volcanos. The oldest part of the earth's crust is under Greenland and Canada, dating back 4,000 million years. The crust under the oceans are much younger, the oldest being 200 million years old. The deepest hole bored into the crust reached 9 miles and was in the Kola Penninsula of Artic Russia.

The earth is not solid. Under the crust is warm slow moving mantle, before reaching the outer core, 77 miles down, containing molten rock. The inner core, 1.800 miles down, with a heat of 1,500C, is solid. It cannot melt, due to the high pressure, and is the same size as Mars. The inner core was discovered in 1936 when it was found that earthquake waves were deflected in the centre, which would not happen if the core was liquid like the outer core.