LET'S EXPLORE The Earth
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Let's explore the Earth
The Earth is a huge, spinning ball of rock with a core of iron. It is one of eight planets that travel round the Sun. It is the only world we know where life exists. Its surface is made up of oceans, which cover more than two thirds of it, and land masses, called continents. A layer of air called the atmosphere, surrounds the Earth.
Orbit
The Earth orbits the Sun in just over 365 days, which we call a year. The Earth spins on its axis (an imaginary line running from north pole to south pole) once every 24 hours, or a day. This makes the Sun appear to rise at dawn, pass across the sky and set at dusk, giving us day and night.
While the Earth orbits the Sun, it is itself orbited by the Moon. It takes a little more than 27 days to go round the Earth.
Shape
The Earth is not quite a perfect ball or sphere, but slightly squashed at top and bottom. This shape is known as an oblate spheroid (as in this illustration, although the Earth is not as squashed as this). The distance around the Equator (the line around its middle) is 40,075 kilometres (24,900 miles), and 40,008 kilometres (24,850 miles) from one pole around to the other and back again.
Inside the Earth
The Earth is made up of a number of different layers. Its outer layer, called the crust, is a thin, rocky shell. Beneath the crust lies the mantle. This is a thick layer made of hot, dense rock, some of it molten, or liquid. At the very centre of the Earth is its core, a ball of metal, liquid on the outside, solid on the inside.
Earth's surface
The Earth's land areas are constantly being shaped by the weather and by moving water and ice. Unlike the other rocky planets, whose surfaces are barren, much of Earth’s is covered by vegetation. This includes forest, scrub, grassland and crops.
Different regions have different climates, long-term patterns of weather. This plays a vital role in deciding which types of plants and animals live where. Large parts of the Earth show the important influence of the human population: for example, farmland, roads and cities.
Water
Earth is the only world where liquid water is known to exist at the surface. Oceans store about 97% of it. The rest is found in rivers, lakes, reservoirs or under the ground. Water is also present as droplets or ice particles that make up the clouds, as water vapour in the atmosphere, and as ice in polar regions or in glaciers.
Atmosphere
The atmosphere is an “ocean of air” that surrounds our planet. It is a mixture of gases, mainly nitrogen and oxygen. It gets thinner the higher you go, and fades away completely about 800 kilometres (500 miles) above the ground.
The atmosphere provides oxygen for us to breathe. It traps enough heat to avoid extremes of hot or cold. It also shields us from the Sun's harmful rays and protects us from bombardment by meteorites or asteroids. Without the atmosphere, life on Earth would be impossible.
Consultant: Ian Fairchild
Ready to find out more?
Here are some pages in other parts of Q-files you might like to explore:
Planet Earth
Planet Earth A-Z
Earth
Earth's interior
Atmosphere