The Solar System

Earth

The Earth is the third planet in our solar system and the fifth largest of all the eight planets. It is about 150 million km away from the sun, and the only planet known to have life. The Earth is not a perfect sphere. It is a bit flatter at its poles and wider at the equator. The planet rotates on its axis once every 24 hours. At the equator, it spins at a speed of 1600 km an hour.

Life on Earth exists because there is oxygen in the atmosphere, the temperatures are moderate and about 75 % of the planet is made up of water. The atmosphere is filled with lots of particles - gas, water vapour, dust, dirt etc.. When light from the sun hits these particles it is scattered in all directions. The blue light reaches our eyes from all directions. The other colors go straight to the surface. That is why the sky is blue. To the astronauts in space, the sky is dark black.

The sun is so powerful that it would burn everything on our Earth and make our planet unliveable. We are lucky to have protection - the ozone layer. It is about 20 - 40 km above the Earth's surface and it protects us from the dangerous ultraviolet rays of the sun. Without it many of us would have skin cancer and most plants and animals wouldn't be able to live. In the past years scientists have found out that the ozone layer is becoming thinner and thinner because people are using too many chemicals on our Earth.

The Earth is made up of three parts :

• The core is the inner part. It is probably made up out of liquid iron and nickel. It is the heaviest part of our planet. Temperatures in this part may be as high as 6000° C.
• The mantle is the middle part. It is made up out of rock that has been melted.
• The crust is made up out of cold rock that cooled down millions of years ago.

There is a very powerful magnetic field around our Earth. It is as if there was a great magnet in its core. The magnetic North Pole is not the same as the geographic North Pole. It is the place where a compass needle shows to. Currently, they are about 1200 km away from each other. The magnetic poles of the Earth are moving all the time and never stay in one place.

Our planet is about 4.5 billion years old. At first the Earth was a great ball of gas and dust. Then it lost a lot of its heat and became cooler. The lighter rocks floated to the surface and the heavier ones sank down to the core. Later on, gas and liquid rock from the inner part of the Earth came to the surface in the form of volcanic eruptions.

Water vapour cooled down and turned into water - today's oceans. The gases, mostly nitrogen and carbon dioxide were kept in the atmosphere by the Earth's gravity.