My Science School

Some mountains are no more than steep hills covered with grass and trees. Others rise high into the atmosphere with snow-covered peaks. Often mountains stretch out in long chains called mountain ranges.

Mountains are formed over long periods by tremendous forces in the earth. These forces move parts of the earth’s crust in different ways, making different kinds of mountains.

Mountain ranges are important because they influence the climate and water flow of the land around them. How do they do this? Air cools as it reaches high altitudes. And cold air holds less water than warm air does. So as the warm air turns cooler near the tops of the mountains, it releases water in the form of rain or snow. This rain or snow feeds nearby rivers and streams. Mountains are also important as homes for plants and animals and as a source for minerals.

Scientists say the earth’s mountains are millions of years old. The youngest mountains have rugged, sharp peaks. Older mountains are smoother, with rounded tops. These older mountains have been worn down by wind and rain over millions of years.

But all mountains begin to wear away, or erode, even while they are rising. Rainfall washes away tiny pieces of rock. The wind carries away dust and earth.

Water seeps into cracks in the rock and freezes. Ice takes up more space than water, so it forces the cracks open. This happens over and over until rocks break off and fall down the mountainside. After millions and millions of years, all of these forces wear away the mountains.

There are five different kinds of mountains.

Fold Mountains form when sections of the earth’s crust meet head-on. This makes layers of rock in the crust crumple and fold. They often make wave-like patterns.

Fault-block Mountains form when earthquakes make the earth’s crust break into large blocks that are tilted or pushed out of place.

Dome Mountains form when forces inside the earth push the earth’s crust up into a huge bulge or dome.

Erosion Mountains form when rivers or glaciers flow over a high, flat area of rock. They wear it away to form peaks and valleys.

Volcanic Mountains form when molten rock from deep within the earth erupts. It pushes up through the earth and piles up on the surface.

The Earth’s Plates

It may seem that the earth’s crust is one gigantic piece of rock. But the outer shell of the earth is divided into about 30 large and small pieces that fit together like a puzzle. These pieces are called tectonic plates.

The plates move on a very hot layer of rock within the mantle. The plates move very slowly, only from 1.3 to 20 centimetres per year.

The continents sit on top of the plates. When the plates move, they take the continents with them. But the plates aren’t only under the continents. They are also under the ocean floor. They are under water on the continents, such as lakes and rivers, too.

Under land, the plates are about 100 kilometres thick in most places. In some places in the world’s oceans, they may be less than 8 kilometres thick.

As the plates move, the continents and oceans slowly change. Scientists think that in 50 million years, South America and Africa will be further apart. They think the Atlantic Ocean will be wider, and the Pacific Ocean will be smaller.

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Some of the world’s best detectives are the people who study the earth. They are called geologists.

Geologists help us learn about the earth’s resources and how to care for them. They tell us how to preserve these resources and to use them properly when we must. Some geologists study where to build homes, bridges, and dams safely. These scientists also work to protect people from earthquakes, floods, and other natural disasters.

Geologists may be found chipping rocks on a mountainside or drilling on the ocean floor. Sometimes geologists work indoors. They X-ray rock samples, do research and tests on computers, or make maps of places they want to explore.

Geologists may travel all over the world. They search mountains, swamps, deserts, and the bottom of the ocean, so that we can learn more about the earth. They may tramp through rain forests, go underground into mines, or climb around an icy glacier.

Geologists and many other kinds of scientists uncover the secrets of the earth in different ways. Sometimes such scientists are called earth scientists.

Environmental geologists work to solve problems of pollution. They search for the best ways to get rid of hazardous waste - materials that are dangerous to our health.

Meteorologists study the weather and the air that surrounds the earth. They predict weather conditions.

Mining geologists study the earth’s rocks and ways to remove them.

Mineralogists identify and study the 3, 000 or so kinds of minerals found on the earth.

Petroleum geologists search for oil and natural gas on land and beneath the ocean floor.

Seismologists study the motion of the earth. They watch for earthquakes. Most earthquakes occur underwater.

Geochemists study the chemicals in the earth’s crust, its waters, and its atmosphere and why they are there.

Palaeontologists study fossils of animals and plants to learn about the earth’s past.

There are many kinds of earth scientists, but they have one thing in common. They all enjoy studying the earth and want to uncover its secrets.

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Maybe you have used oil on your bicycle chain to keep it from squeaking. Did you know that oil was once part of the earth? It starts as a thick dark liquid called crude oil that is found between layers of rock deep inside the earth’s crust. Crude oil is also called petroleum.

Crude oil is a fossil fuel. This means that it started forming millions of years ago from dead plants and animals that had lived in the ocean. Over millions of years, these dead plants and animals piled up on the ocean floor. Thick layers of sand and soil covered them. The sand and soil squeezed together under their own weight and the weight of the water pressing down on them. They were pressed so hard that they turned into rock. Scientists believe that the weight of the rock helped turn the piles of dead plants and animals into oil.

People today use oil for many things. They use oil to heat homes and to run cars, planes, trains, ships, and trucks. They also use oil to make such things as medicines and plastics.

Oil companies get oil by drilling into the earth’s crust. They pump out the oil that is trapped under the earth’s surface. They even pump oil from under the ocean floor.

Because of its many uses, oil has become very valuable. But it takes millions of years for the earth to make more oil, so we need to make sure we don’t waste it.

Imagine a giant dinosaur moving along a lakeshore 80 million years ago. It is searching for food. The dinosaur sees some plants and wades out to them. But before it reaches the plants, it steps into a deep hole filled with soft, wet mud. The dinosaur sinks deeper and deeper into the mud, and the dinosaur drowns.

Over time, the soft parts of the animal’s body rot away. Only its bones are left, covered by mud. For many years, layers of sediment pile on top of the mud and pack it tightly around the bones. Eventually, the packed mud turns to clay. After many more years pass, the clay turns to rock.

During all this time, minerals in the water of the lake fill the hollow places in the bones. The minerals harden and the skeleton of the dinosaur is preserved. The bones in the rock are called fossils.

There are other ways for fossils to be made. And, fossils exist for many kinds of living things - from bugs to plants to woolly mammoths - not just for dinosaurs.

Metals are found in earth’s rocks. In order to use the metal, the kind of rock that contains the metal must be mined, or dug out of the ground. This rock that contains the metal is called ore.

Many ores are found beneath the ground in layers of rock called veins. Iron ore is mined. After it is mined, the ore is smelted. Smelting removes metal from the ore. The ore is put into a huge furnace and mixed with other rocks. Hot air is blasted into the furnace. When the furnace is hot enough, the liquid iron sinks to the bottom. It then is poured into a container that holds many tonnes of molten, or melted, iron.

Steel is made by heating iron and mixing it with a small amount of a chemical called carbon. Steel is used to make such things as car parts, buildings, screws, and paper clips.

Aluminium is light, strong, and doesn’t rust. It comes from an ore called bauxite. To make aluminium, the compound called alumina must be removed from the bauxite. Aluminium is used for many things, including pots and pans, aeroplane parts, and chewing gum wrappers.

Gold and silver ores are hard to find and sometimes are found as natural metals. Both are heavy, but very soft. Gold and silver are used in coins and jewellery.

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Precious Stones

They shine, they sparkle, and they flash and shimmer. They are only stones, small pieces of minerals, but they are so beautiful and hard to find that they are precious. Precious means “having great value”. Diamonds, rubies, emeralds, sapphires, and opals are examples of precious stones or gems.

Diamonds come from deep inside the earth. They are buried in rock that is in or near volcanoes that are no longer erupting. When first taken from the ground, diamonds are dull and greyish. After they are cut and polished, they sparkle.

A diamond is the hardest of all things. It is so hard that it can even cut rocks. The only thing that can scratch a diamond is another diamond.

Corundum is a common mineral. But when tiny bits of other minerals are added, it becomes a precious stone. With a bit of titanium and iron mixed in, it becomes a clear, blue sapphire. With chromium mixed in, it becomes a dark red ruby. With beryl mixed in, it becomes a deep green emerald.

On the coast of Northern Ireland, 40,000 mysterious columns of stone rise out of the sea like huge stairs. The unusual rocks cover a length of beach about 5 kilometres long! They are called the Giant’s Causeway.

Ancient stories tell about a king who built a causeway of stepping stones between two countries. The stones joined Ireland and Scotland and had to be large enough for giants to walk on them.

It is not surprising that people long ago invented such a story, because the real stones on Northern Ireland’s coast are very strange. Each measures about 46 centimetres across the top. And every one of them has six sides. They look as if they must have been made by human beings, but they were not. They were made by a volcano.

Long ago, magma exploded from deep inside the earth. As it cooled, it shrank into a hard rock called basalt. As it became cold, the rock split into long columns.

In Northern Ireland, the columns have six sides, but basalt columns found elsewhere may have only four or five sides. A whole cliff of basalt columns can be found in central California, U.S.A. It is called the Devil’s Postpile and looks like a giant’s supply of fence posts.

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Minerals Everywhere

It takes a lot of ingredients to make biscuits - flour, milk, eggs, butter, and sugar. Everything is all mixed together. A rock is like that. Rocks are mixtures of materials called minerals. There are about 2,000 kinds of minerals. Some are hard, some are soft, some are shiny, and some are sparkly. Many of them are mixed with other minerals. But some are found in chunks, small lumps, or broad patches between layers of other kinds of rocks.

Most kinds of minerals are made up of tiny shapes called crystals. Crystals have flat sides and sharp corners. The salt we put on food is a mineral called halite. It is made up of crystals shaped like cubes. Quartz crystals have beautiful pointed shapes. Sulphur crystals look like chunks of bright yellow glass. Pure mercury is a mineral that stays melted, even when cool. Mercury is used in some thermometers. Uranium has flat sides and a dull colour. It is never found alone, but always is mixed with other minerals. Uranium is sometimes used as a fuel in making electricity.

The Rock Factory

The earth is a huge rock factory. Scientists believe it has been making rocks for billions of years.

The earth makes three kinds of rocks. One kind is made from hot, syrupy liquid rock, deep inside the earth. The melted rock is called molten rock. Sometimes, some of this liquid rock pushes its way between two layers of solid rock, making a sort of rock sandwich. Then the liquid cools and becomes solid, too. Other times, when volcanoes erupt, some of the liquid rock is pushed up out of the earth. When it reaches the earth’s surface, it cools and becomes solid.

This type of rock that was once a hot liquid is called igneous rock. Igneous means “formed by fire”. Granite, the grey rock used on the outside of many buildings, is an igneous rock. And so is the black, glassy rock called obsidian that some prehistoric people made into arrowheads.

Another kind of rock is made out of “rock powder”. Wind and rain wear away bits of larger rocks. Rivers carry the powdery bits to the ocean. There, with other bits of things, they sink to the ocean floor and form a layer called sediment. Sediment comes from a word that means “to settle”. Over thousands of years, the bottom layers of powder are squeezed together by the weight of new layers. Slowly, the powdery bits on the bottom are turned into a layer of solid rock.

Over millions of years, earthquakes and other forces may lift up the layers of new rock until they become dry land.

Rocks that are made this way are called sedimentary rocks. Limestone and sandstone are sedimentary rocks.

The third kind of rock the earth makes is made deep under the surface. The heat and the weight of other rocks slowly change these rocks into a different kind of rock. Their new form is called metamorphic rock. Metamorphic means “changed”.

Marble is a metamorphic rock that changed from limestone. Slate is a metamorphic rock that was changed from mud. Most metamorphic rocks are very old. They stay underground unless erosion, an earthquake, or a new mountain brings them to the earth’s surface.

All the rocks you see were made long, long ago. The oldest rocks ever found on the earth are more than 3 billion years old. But the earth hasn’t stopped making rocks. It’s making them right now. It’s always wearing away old rocks and building up new ones.

Could you dig a hole to the other side of the earth? No, it’s not possible. The centre of the earth is about 6,400 kilometres beneath your feet. So it’s almost 13,000 kilometres to the other side of the earth. It’s too far to dig. And for most of that distance, the earth is either solid rock or metal so hot that it’s melted! Nobody could dig through that!

But if people could dig a hole through the earth, they would first have to go through a shell of rock. This rock formed long ago, when the outside of the earth cooled down. This rock is called the earth’s crust. The oceans and the continents cover the crust.

Under the crust is another layer of rock. It is called the mantle. The mantle is made of a different kind of rock than the crust. The deeper the mantle goes, the hotter it gets. At its bottom, it is hot enough to melt iron.

Beneath the mantle is a layer of melted metal - metal so hot that it’s thick like syrup! This layer is called the outer core.

In the very centre of the earth is the inner core. It’s a ball of hot, solid, squeezed-together metal.

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The outside of the Earth

Take a walk and touch the outside of the earth with your feet. Dig a small hole and feel the soil. Splash in a stream. Take a deep breath of the air that surrounds you.

You live on the surface of the earth. The surface, or crust, of the earth is made of rock. In some places, it is covered with soil. In many places, it is covered with water. All around it is air.

Most people live on huge pieces of land called continents. A continent is a huge platform of rock that sticks up higher than the rest of the earth’s rocky crust.

Some people live on smaller pieces of land called islands. Some islands are the tops of underwater mountains or volcanoes. Other islands are formed from sand or coral. Still others are pieces of land that have become separated from a continent.

The continents and islands are surrounded by water. Water covers almost three-quarters of the earth’s surface.

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Why isn’t it round and flat like a pancake or square like a block? Why does it spin? And why does it whirl around the sun?

Most scientists think the answers lie in the earth’s beginning. They think it began billions of years ago with a gigantic, spinning cloud of dust and gas in space.

The earth was one of the balls that formed from the dust and gas. As the earth’s gravity pulled in more and more dust and gas, everything squeezed together, tighter and tighter. The ball grew hotter and hotter. It became so hot that bits of dust, mostly rock and metals, melted together. The earth glowed!

The outside of the earth didn’t stay hot. The melted rock cooled. As it cooled, it hardened. It became a ball of hard rock and metal, as it is today. But the inside of the earth never cooled. The centre of the earth is fiery hot. Heat is always flowing from it, and parts of it are still melting.

Bit by bit, we are finding new clues about the earth’s beginning. There are lots of stories and beliefs of how the earth began. But nobody really knows exactly what happened.

Moving Around the Sun

The earth does more than just spin. As it spins, it moves through space.

The earth travels through space around the sun at a speed of about 107,200 kilometres an hour. But it isn’t moving in a straight line. Instead, it whirls around the sun in a large, almost perfect circle. This path the earth takes around the sun is called an orbit.

What keeps the earth moving around the sun? Why doesn’t it move all over space?

Everything in space pulls at everything else. This pull is called gravity. The bigger a thing is, the stronger its pull. The sun is more than a million times bigger than the earth, so it tugs hard at the earth. It is this strong tug that keeps the earth in orbit.

The time it takes the earth to go all the way around the sun is a little more than 365 days. This is what we call a year.

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The Spinning World

Did you ever think you could spin around and around without getting dizzy? Well, that’s what happens to you every day and every night. The earth is spinning around like a huge top, and you’re along for the ride!

Both the earth and a top spin around an axis, like a wheel spins around its axle. See for yourself. Push a stick through a ball of clay. Twirl the stick, and the ball will spin around.

Now imagine a pole going through the centre of the earth. That imaginary pole is called the earth’s axis. One end of the earth’s axis is called the North Pole. The other end is called the South Pole. The earth spins around its axis, like a wheel spins around its axle.

People can’t feel the earth turn because it is so big. But we know it does turn because that’s what gives us our day and night. In the morning, when the sky is bright, we know that our part of the earth is turned towards the sun. At night, when the sky is dark, we know that we’ve turned away from the sun.

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