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.