KHOWLEDGE ZONE

They can cut metal. They can cut glass. They are billions of years old and form deep within Earth. Some are so rare and beautiful that people will pay a fortune to get one! They are diamonds.

WHAT ARE DIAMONDS?

Diamonds are made of carbon, a chemical element. That’s the same stuff that’s in the tip of a pencil. But isn’t carbon soft, not hard?

Pencil carbon is so soft that it rubs off on paper. But diamond carbon is so hard it can cut almost anything. In fact, diamonds are the hardest things in nature. What makes the difference? The atoms inside a diamond have a special crystal shape. This makes them very hard.

Some diamonds can sparkle brilliantly. Such diamonds are rare. They are precious and valuable, and people wear them as jewelry. But most diamonds are small and contain flaws. These are worth much less.

HOW DO DIAMONDS FORM?

Big diamonds form deep under the ground. The heat and pressure at great depths melts carbon-rich rocks. Diamonds form out of this molten (melted) rock. The diamonds are later brought to Earth’s surface by currents of molten rock. The entire process can take billions of years!

Smaller diamonds can form closer to Earth’s surface. Movements of the planet’s crust lift these stones up from the depths.

WHAT CAN DIAMONDS DO?

You can scratch or cut just about anything with a diamond—except another diamond. On a scale of hardness from 1 to 10 with 10 as the hardest, diamonds are a 10.

Because they are so hard, diamonds are great for drills, saws, and other cutting tools. That makes them very useful in mining and manufacturing.

SYNTHETIC AND IMITATION DIAMONDS

Are there any shortcuts to making diamonds? Actually, there are. People have learned how to make artificial diamonds and other gems. Diamonds made by people are called synthetic diamonds.

Synthetic diamonds look and act like the real thing. They’re as hard as natural ones. In fact, most diamonds used for industrial purposes are synthetic.

Imitation diamonds aren’t diamonds at all. They’re usually made from inexpensive materials that sparkle brightly, such as quartz or glass. But they aren’t as hard as natural or synthetic diamonds. Imitation diamonds are used mostly in jewelry.

WHY ARE DIAMONDS CUT?

Diamonds found in the ground are rough. They don’t shine like the gems in jewelry stores. They look greasy or dirty. So how do you make diamonds really sparkle? You cut them.

Cutting a diamond gives the stone edges that bring out the shine. Diamond cutters trim away flaws such as cracks or cloudy spots.

It takes careful planning to cut a diamond. The goal is to make the diamond as large and as valuable as possible. Even so, a cutter slices away about half of a diamond’s original size. After polishing, the cut diamond is ready to sell.

WHAT MAKES DIAMONDS WORTH SO MUCH?

Diamonds are judged by the “4 Cs.” These are color, clarity, carat weight, and cut.

Color: When diamonds form, small amounts of minerals get inside them. This changes their color. Colorless stones are very desirable. Yellowish or brownish ones are not.

Clarity: Can you see flaws in the diamond? A diamond with great clarity has no visible flaws. The clearer a stone is, the greater its value.

Carat weight: The heavier a diamond is, the better. Because large, heavy diamonds are less common, they are more valuable. A diamond that weighs 2 carats or more is usually considered large.

Cut: Diamond cutters decide on the shape and proportion of a stone. An attractive cut makes a diamond more desirable.

HOW BIG CAN DIAMONDS GET?

The largest natural diamond ever found is the famous Cullinan diamond. It was discovered in South Africa in 1905. The Cullinan tipped the scales at an amazing 3,106 carats!

What do you do with a diamond that big? The Cullinan was cut into 105 different gems. The largest of these is called the Star of Africa. It is the largest cut diamond in the world. Today, the Star of Africa sits on the end of the British royal scepter.

Take a really deep breath. Feel how your chest gets bigger and bigger. Your chest gets bigger because your lungs are filling up with air. You cannot see air, but air is all around you. You can feel it when the wind blows.

Earth’s atmosphere is made of air. An atmosphere is made up of the gases that surround a planet.

WHAT IS AIR?

Air is a mixture of several different gases. The main gases in air are nitrogen, oxygen, and argon. Air also contains smaller amounts of hydrogen, carbon dioxide, water vapor, helium, and other gases. Oxygen is the most important gas for animals. Animals must breathe oxygen in order to live.

Carbon dioxide is the most important gas for plants. Plants use carbon dioxide and sunlight to make food. Plants give off oxygen. Animals turn the oxygen back into carbon dioxide when they breathe.

TAKING AIR WITH YOU

You can go to places where there is no air. There is no air underwater, but you can dive underwater. You can stay underwater a short time just by holding your breath. Air tanks let you stay underwater for a long time. Scuba divers wear tanks on their backs. The tanks are filled with gases that make up air. The divers breathe the gases through hoses.

There is less and less air the higher up you go. People gasp for breath at the tops of tall mountains. Airplanes must carry air. Once the airplane gets up high, air is pumped into the cabin where passengers sit. Astronauts have to take all the air they need with them—there’s no air in space!

Pretend you are an alien explorer from outer space looking for life on other planets. Your spaceship flies into a group of stars that looks like a gigantic whirlpool. The whirlpool is the Milky Way Galaxy.

You head for a star with nine planets in one arm of the Milky Way. The third planet from the star is a beautiful blue, white, and green ball. This planet looks like it has life. The name of this planet is Earth.

HOW DOES EARTH MOVE IN SPACE?

Earth spins like a top on its axis. Earth’s axis is an imaginary line that goes through Earth from the North Pole to the South Pole. Earth’s axis is slightly tipped, like a spinning top leaning to one side.

Earth travels around the Sun at about 67,000 miles per hour (about 107,000 kilometers per hour). One year is one trip around the Sun. Earth’s path around the Sun is slightly oval-shaped. This oval shape causes Earth’s distance from the Sun to change during the year.

WHAT MAKES DAY AND NIGHT?

The Sun seems to rise in the morning, cross the sky during the day, and set at night. However, the Sun does not actually move around Earth. Earth’s turning on its axis makes it look as if the Sun is moving.

Earth makes a complete turn on its axis every 24 hours. As Earth turns, half of the planet faces the Sun, and the other half faces away. It is daytime on the half facing the Sun. It is night on the half facing away from the Sun.

WHY ARE THERE SEASONS?

Earth has seasons because of the tilt of its axis. For part of the year, the top half of Earth is tipped toward the Sun. The top half of Earth is called the Northern Hemisphere. During another part of the year, the bottom half of Earth is tipped toward the Sun. The bottom half is called the Southern Hemisphere. It is summer in the half that is tipped toward the Sun. It is winter in the half tipped away. When it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere. During spring and fall the hemispheres are tipped neither toward nor away from the Sun.

The equator is an imaginary line around Earth’s middle. The farther you are from the equator, the greater the difference in temperature between seasons. The equator never tips far from the Sun. Near the equator it is warm enough to go swimming all year long. The average temperature barely changes from month to month. In Alaska, far from the equator, the average temperature in January can be more than 60 degrees colder than it is in July.

WHY IS THERE LIFE ON EARTH?

Earth has just the right conditions for life. It is not too hot or too cold. Earth has lots of liquid water and an atmosphere (gases) that can support life.

The first kinds of life may have appeared on Earth 3.8 billion (3,800,000,000) years ago. Several times during Earth’s history, almost all life went extinct, or disappeared. Each time, some life forms survived. The survivors spread all over the planet. Dinosaurs appeared about 230 million years ago. Dinosaurs went extinct about 65 million years ago. Scientists believe that modern humans appeared about 130,000 years ago.

WHAT IS THE INSIDE OF EARTH LIKE?

Earth is made of layers. The top layer is called the crust. It is made of hard rock and soil.

More than 70 percent of Earth’s crust is covered with water. Most of the water is salt water in the ocean. Pieces of dry land called continents rise above the ocean. The part of Earth’s crust under the ocean is called the seafloor.

Under the crust is a layer of partly melted rock called the mantle. Under the mantle is Earth’s core. The core is mostly iron. The outer part of the core is liquid metal. The inside of the core is solid metal. Scientists believe that the liquid metal makes Earth a giant magnet and creates Earth’s magnetic field.

Earth’s crust is made of gigantic slabs of rock called plates that move over the mantle. Plates crash together to make mountains. They pull apart and let red-hot rock ooze up from inside Earth to make new crust.

HOW DID EARTH FORM?

Scientists think that Earth and the rest of the solar system formed from a spinning cloud of gas and dust. Gravity pulled most of the gas and dust together to form the Sun. Some leftover gas and dust formed Earth and the other planets. Scientists think that Earth and the Moon formed about 4.6 billion years ago.