The Blue Planet Earth

The picture above shows our Earth, photographed by astronauts on their way back from the Moon. It is a huge, round sphere. Seen from space, Earth appears blue, which is why we also call it the “Blue Planet.” Its surface is largely covered by water, and water reflects mainly the blue parts of light.

We live somewhere on this globe, along with all other people, animals and plants. We can make out Africa, Arabia and Antarctica. The Mediterranean Sea can be seen at the upper left edge. The large blue areas are oceans. Clouds drift above much of the globe.

Our home, Earth, is a unique place in space. It has mountains, streams and lakes, deserts and primeval forests. We humans have built houses and cities and thoroughly changed the Earth's surface. Cars travel on roads, and planes fly high above the ground.

Above all, though, apart from Earth, we have not yet found any other celestial body on which living beings exist. 

Earth is a planet because it is a celestial body that orbits a star. Stars, on the other hand, are extremely hot and give off light and heat. A planet only shines because light from a star falls on it. It reflects that light.

Like the Sun, planets are spherical bodies. Some planets have moons orbiting them. Our Sun has eight major planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All these planets orbit the Sun.

The Earth seems enormous to us. Compared with other celestial bodies, however, it is tiny. Its diameter is just over 12,700 km. Anyone travelling around it at the equator covers 40,075 km.

The Earth spins on its axis. It takes exactly 23 hours, 56 minutes and 4.1 seconds to complete one rotation. It also takes 365 days, 5 hours, 48 minutes and 45 seconds to orbit the Sun once. We call this period a year. The Earth travels 29.780 km every second as it orbits. That is a speed of more than 107,000 km/h. But we don't notice it.

Without the Sun, there would be no Earth. It provides us with light and warmth. Earth is about 150 million kilometres from the Sun. That distance is just right: not too hot and not too cold. And because there is water on Earth, life was able to develop here.

The Earth formed about 4.6 billion years ago. At that time, there was a huge cloud of hydrogen and dust. Most of this “solar nebula” contracted more and more under the force of gravity. The Sun formed at its center. The rest of the solar nebula began to revolve around it.

Collisions and the force of gravity first caused small balls of dust to form. They attracted more and more dust and gas, and many eventually grew into large bodies. But only eight of them managed to become planets, attracting all the matter around them and steadily increasing in mass.

The planets Jupiter, Saturn, Uranus and Neptune are made mostly of gas, which is why they are known as “gas giants.” Like Mercury, Venus and Mars, Earth formed mainly from solid materials such as iron and rock.

The Earth is surrounded by its thin crust. It is only about 30 to 50 kilometres thick and is very uneven. The Earth’s crust consists of several enormous plates. These plates push against one another, forming mountains. Sometimes the plates suddenly shift against each other, causing earthquakes.

The highest mountain on Earth, Mount Everest, rises to 8,848 m. The lower-lying parts of Earth’s crust are covered by the waters of seas and oceans. The deepest point lies in the Mariana Trench in the Pacific Ocean. It is 11,034 meters below the surface of the sea.

The Earth's crust may seem solid to us. But in reality, it “floats” on a thick layer of hot, viscous magma. We call this layer the mantle, which is divided into the outer and inner mantle. In some places, the mantle's magma pushes through the Earth's crust to the surface. This creates volcanoes, which spew out gases, rock, and molten lava.

At a depth of about 2,900 km, the temperature is around 3,000 °C. This is where the Earth’s mantle meets its core. The core has two layers: the inner core and the outer core. These layers consist of molten iron and nickel. Temperatures in the Earth’s core rise to around 4,700 °C.

The Earth is surrounded by a layer of air made up mainly of nitrogen and oxygen. We call this layer the atmosphere. It is essential for human beings and all other living things. Four out of every five particles in the air are nitrogen, and only one is oxygen. However, humans could not live without oxygen. It is mainly the plants on Earth that constantly produce new oxygen.

The atmosphere also ensures that there are only small differences between daytime and nighttime temperatures. The average temperature of the atmosphere can fluctuate greatly. When it is low, ice ages occur and plant growth declines. When it rises, deserts can form, glaciers melt, sea levels rise, and heavy rain and flooding occur.