Soil, sand, and dust

Tiny chips of rock and powdered flower petals. Bits of bats' wings and birds' feathers. Fragments of dried-up caterpillar skin and pieces of mouse whiskers.

That isn't a recipe for a magic potion. It's the "recipe" for soil ! Soil is tiny bits of rock mixed with tiny bits of dead plants and animals. When plants and animals die, their bodies decay and fall apart. Rain washes them into the ground, to mix with the rest of the soil.

Sand is tiny bits of rock. Wind, water, and the roots of plants all help to make sand. Wind blowing against rock wears off tiny bits of it. Rain falling on rock, and waves smashing against it, also break off bits. The roots of plants dig into rock and split it into small pieces.

Dust is made up of tiny, tiny bits of sand, soil, animal hairs, bits of plants, and other things carried into the air by the wind. The dust floats in the air for a time, then drifts back to earth again.

Icy bulldozers

Some of the snow on a high mountaintop melts and run off. But much of it stays all year round. The snow that stays becomes hard and grainy, like salt. As new snow falls each year, the grainy snow underneath is squeezed together and becomes hard as ice.

The weight of all the snow pressing down squeezes out a stream of ice, like toothpaste is squeezed from a tube. This gigantic stream of ice, creeping down the mountainside, is called a glacier.

There are two main kinds of glaciers. One kind is like a river of ice. It stretches from near the top of a mountain down into a valley below. The other kind of glacier is like an enormous cake of ice and snow. This kind covers whole mountain ranges and even whole lands. All the land at the South Pole is covered by such a glacier.

Most glaciers move slower than a snail. They travel only a few inches (centimeters) or feet (meters) in a whole day. But, slow as it is, a moving glacier is like a big, icy bulldozer. It scrapes, gouges, and shovels up the ground over which it moves. It picks up everything in its path, from soil to huge boulders, and carries it along. As a glacier passes through a valley, it may dig the valley deeper and wider. As it moves down a mountainside, it may leave long scratches and furrows.

Glaciers make valleys wider and dig out holes for lakes. Long ago, during the time that is called the Ice Age, great glaciers crept far across the land. They dug many ditches and deep holes in some of the places they passed over. Later, these holes filled up with water and became lakes. In some places the glaciers left rich soil that they had picked up as they moved. In other places, they left behind huge boulders that now sit far from the mountains that were once their home.

Lands of ice

Two parts of the earth are bitter cold all year round. These places are the "top" and the "bottom" of the earth - the North Pole and South Pole.

The land around the South Pole is called Antarctica. It is the coldest place on earth. Antarctica is covered with a sheet of ice more than a mile (1.6 kilometers) thick. But beneath the ice there is land, just like other land, with mountains, plains, and valleys.

At the North Pole there is no land. This part of the world is just a huge sheet of ice from four to ten feet (1.2 to 3 meters) thick. Beneath the ice there is only the water of the Arctic Ocean.

Scientists know that ten or twenty million years ago there was no ice at the North and South poles ! Palm trees grew in Antarctica, and animals such as those that now live only in hot places lived there ! But something happened to turn the two poles into regions of ice.

We don't know why the poles became covered with ice, but we know why the ice does not melt. It is because the sun never shines directly down on the poles. Because the sun is usually low in the sky, the air stays cool. Thus, the poles get much less heat than the rest of the earth. And most of the heat they do get bounces off the shiny, white ice and is reflected back out into space. So the poles never get enough heat to melt all the snow and ice.

Land in the water

Explosion after explosion of hot rock and ash spurted from the ocean. A thick cloud of steam rose high into the air. Slowly, for many days, a long mound of dark lava rose up out of the water. An island had been born !

An island, of course, is a piece of land with water all around it. But the land doesn't float on the water. What you see is the top of land that sticks up from the bottom of the sea. Most islands far out in the ocean are actually the tops of underwater volcanoes !

Volcanic islands are made when underwater volcanoes erupt, pouring out red-hot, melted rock. The rock quickly cools and hardens in the water, building up into a big, cone-shaped mountain. The island is the top of the cone.

All islands aren't volcanoes. Most islands in lakes and rivers are high pieces of land that stick out of the water. Some islands are formed when the sea separates them from the mainland. Great Britain was not always an island. But the land that joins it to Europe was last covered by the sea thousands of years ago.

Dry lands

The golden, glowing sun glares down on a vast sea of sand. As far as the eye can see, the sand stretches in great yellow-brown ripples. The air is so hot you can see it shimmer as it rises from the sand. There is not even the tiniest green plant anywhere in sight.

Whenever most people think of a desert, they usually think of an endless, hot sandy land. But there are actually many different kinds of deserts.

Some deserts are rolling, sandy places where hardly any kind of plant can grow. Some are flat plains that are covered with many kinds of plants. Even the world's biggest, hottest desert, the Sahara, has small patches of trees and grass in some places. Such a patch of greenery is called an oasis.

Some deserts are hot all year round. Others are hot in the summer and cold in the winter. Some deserts are great bare places on the shores of seas. Others are rocky places high up in mountains. But all deserts, wherever they may be, are the earth's dry places - places where little rain falls.

It does rain in deserts, but usually only a tiny bit. Some parts of deserts go for many years without rain, then get just a sprinkle. Sometimes a desert is so hot that the rain dries up before it reaches the ground !

But some deserts get cloudbursts. Than, rain pours down on parts of the desert. In fact, the heavy rain may cause sudden floods. The dry earth can't soak up the water fast enough, and water quickly fills up the desert's low places. But soon, the ground is again as dry as an old bone

Scientists can tell that the deserts now on earth were not always here. Most of them are probably only a few million years old. At one time, most of the places we now know as deserts were green and fertile. But something happened. Changes in the wind and weather made rain stop falling on these places. Then, year after year, these lands were baked and dried by the sun until they became the deserts they are today.

Open country

All over the earth there are great flat places. The level or gently rolling land goes on for miles (kilometers). These flat parts of the earth are called plains.

Most plains are lower than the land around them. It might seem, then, that plains would be on the lowest parts of the land. But this is not always so. Coastal plains are low, and usually slope gently upward from sea level. But inland plains, such as the Great Plains in the United States, are often thousands of feet (meters) above sea level.

The lowest place in the world

If the highest part of the land is a mountaintop, where do you think the lowest place must be ? That's right - in a valley. The lowest bit of dry land in the world is the Valley of the Dead Sea, between Jordan and Israel, in the Near East. The land there is 1,299 feet (396 meters) below the level of the nearby Mediterranean Sea.

The Valley of the Dead Sea was not made by a river, as many valleys are. It is foult - a large strip of the earth's crust that has sunk down.

Nature's ditches

What parts of the earth's surface have floors and walls ? Valleys. A valley is like a long ditch scooped out of the ground. The bottom of the ditch is called the floor. The sides are called valley walls.

Some valleys are places where the ground has sunk. But most valleys are made by rivers and streams. As water flows along,it tears away bits of the land. As years go by, more and more land is worn away. The river sinks deeper and deeper. Steep walls form on both sides of it. Then wind and rain begin to wear away the walls, making the valley wider. In time, the valley becomes a long, V-shaped ditch, with the river or stream flowing along the floor.

Some valleys have grown so wide that they are no longer V-shaped. Some are U-shaped. Others have become deeper rather than wider. Very deep valleys with steep walls are called canyons or gorges.

When the earth shivers

"The mountains seemed to walk"

That is what a Chinese writer said about a terrible earthquake he saw. During the worst earthquakes, the ground shivers and shakes and rumbles. Whole sections of land get pushed out of place, so that mountains truly seem to "walk".

Earthquakes begin in the earth's rocky crust. Pressure builds up and begins to push. The force of this push actually bends the rocks, just as you bend a stick. And, suddenly, the rocks snap and break, just as the stick would snap if you kept bending it. This sends shivers through the ground making it quiver and quake.

Earthquakes are actually happening all the time. Every few minutes there is one somewhere in the world. Sometimes an earthquake is very powerful and does a lot of damage. But most earthquakes are so slight they don't even rattle a spoon in a teacup.

Mountains of fire

A volcano is special kind of mountain tha actually builds itself ! It is made of red-hot rock that pours up out of the earth amid earthquakes, explosions, and towering clouds of smoke and ash.

Scientists think that far down in the earth, where it is fiercely hot, there are "pockets" of melted rock. It is thought that the pressure of gas pushes this melted rock, called magma, up out of the ground.

When magma comes out of the ground it is called lava. It may be as thick as syrup or as thin as watery soup, but it cools into a black, gritty rock. It is this rock that builds the volcano. As the lava pours out of the earth, it piles up into the shape of a cone or dome, with a tunnel running down its middle. The more lava that comes out, the higher and wider the volcano gets.

After a volcano has built itself, it may sit quietly for hundreds or even thousands of years. Then, suddenly, the volcano becomes active. The ground begins to shake. Rumbling noises come from deep inside the earth. From the top of the volcano, clouds of dark smoke twist up into the sky. The rumblings become a loud, steady, rushing roar. Magma or hot gas comes surging up through the tunnel. It may burst out of the top of the volcano or flow out of cracks in the side. The volcano has erupted !

There are different kinds of volcanos that erupt in different ways. One kind shoots a stream of glowing lava high into the air, like a giant, fiery fountain. Another kind shoots out solid chunks of red-hot rock and cinders. Some volcanoes pour rivers of lava through cracks in their sides. Some send clouds of glowing, super-hot steam and gas rushing down the mountainside. And some blow themselves to pieces when they erupt !

There are several thousand volcanoes in the world. Many of them do not seem able to erupt any more, and are called "dead" volcanoes. But some volcanoes that have been "dead" for hundreds of years have suddenly become active and had terrible eruptions. And active volcanoes are liable to erupt at any time. Volcanoes have killed many people and destroyed whole cities !

But volcanoes have done good things, too. The ash that comes from volcanoes becomes some of the richest, most fertile soil in the world. And scientists think that, billions of years ago, most of the earth's first air and water came from gas and steam spouted from volcanoes.

The highest place in the world

Where do you think the highest place in the world is ?

As you may have guessed, the highest place in the world is the top of a mountain. It is the top of Mount Everest, which stands between the countries of Tibet and Nepal, in Asia.

When we want to find out how high a mountaintop is, we can't just measure the mountain - we have to measure all the land it's sitting on, too. To do that, we must go to where the land begins - at the top of the sea. That way, we can measure all the land that slopes up from the sea to the very top of the mountain.

When we measure something this way, we are measuring from sea level. All the land in the world is either above or below sea level. The top of Mount Everest, the highest place in the world, is 29,028 feet (8,848 meters) above sea level.

On May 29, 1953, Sir Edmund Hillary of New Zealand and Tenzing Norgay of Nepal became the first men to climb to the top of Mount Everest. Since then, many other climbers have made it to the "top of the world"

The birth and death of a mountain range

Mountain ranges rise where a sea once met a shore. They start to form when a sea bottom along the edge of a continent begins to fill up with mud and sand. As the mud and sand grow thicker, the sea bottom begins to sink. The mud, sand, and rock drop slowly down into the earth's mantle - the hot rock beneath the crust. They are crushed, squeezed, and melted together by heat and pressure. Hot rock from the mantle is mixed ini with them. All this takes many millions of years.

Mountains are orn when this mixture of rock is pushed up again by earthquakes and other forces in the earth. As the huge pile of rock rises, it pushes the edge of the land into wrinkles and folds. After many more millions of years, the upper part of the long, lumpy mass of rock has risen high above the land.

As soon as mountains are born, they begin to wear down. Rain falls on them. Each drop, like a little bomb, breaks off tiny bits of rock. Wind blows off tiny grains of rock and carries them away. Streams and rivers run down the slopes, cutting great grooves. Sometimes, huge masses of ice and snow move down mountainsides, grinding the rock to powder.

For millions of years, all these forces wear tons and tons and tons of rock from mountains. Slowly, the proud, peaked mountaintops are worn down and smoothed out. After many millions of years, nothing is left of a mountain range but a row of small, smooth hills. After more years, even those are worn away.

Giant rocks

Mountains are like great, gray giants. The are huge chunks of rock that have been pushed up out of the earth. Some mountains stand all alone, but most are connected together. Long chains of connected mountains are called mountain ranges.

Mountains are not all alike. Many mountains are bare and rocky. Others have green forests and fields of grass growing on their sides. And most high mountains have snow on their tops all year around. This is because the air on a mountain top is usually cold enough to keep water frozen.

Scientists believe that most of the earth's mountains are many millions of years old. The newest are wrinkled, and have sharp, pointed tops. Older mountains are smooth, with rounded tops. These "old" mountains have been worn down by wind and rain during many millions of years.

The moving continents

It may seem to you that the earth's crust is a single piece of rock. You may think this crust covers the outside of the earth just as an apple's skin covers an apple. But the earth's crust is actually made up of a number of enormous separate pieces, called plates. These plates fit together, like the pieces of a puzzle. And they are all moving, very slowly, in different directions.

Scientists are not sure what makes these huge, curved sheets of rock move. It is thought that the plates slide on the hot, soft rock beneath them. They move only about one inch (2.5 centimeters) or less, a year.

Some of the plates make up part of the ocean floor. Other plates hold the huge, high masses of rock that rise above the sea and form the continents. Thus, as the plates move, they carry the continents and ocean floor with them !

The plates have probably been moving for billions of years. This means that earth's seas and continents have probably had many different shapes ! Scientists think that more than two hundred million years ago the earth's dry land was all bunched together, forming one gigantic continent. Slowly, as the plates moved, the one huge continent broke into two continents. And, as the plates continued to move, both of these continents broke up to form the seven continents we know today.

As the plates keep moving, the continents and seas will keep changing shape. Scientists think that in about fifty million years South America and Africa will be farther apart than they are now. This will make the Atlantic Ocean wider. And Australia may move up and push against Southeast Asia, becoming part of it.