The Earth, showing its internal layers The Earth is a spinning ball of rock and metal. It is one of eight planets that orbit, or circle, our nearest star, the Sun. Its surface is made up of oceans and land masses called continents. A layer of air called the atmosphere surrounds the whole planet. The Earth’s outer layer, the crust, is a thin, rocky shell. Beneath the crust lies the mantle, a thick layer made of hot, dense rock. At the very centre of the Earth is its core, a ball of metal, liquid on the outside, solid on the inside. Earth’s outer shell, called the lithosphere, made up of the rocky crust and partly molten upper mantle, is broken up into a number of large slabs of varying shapes and sizes, called tectonic plates. They are constantly on the move.
The Earth in space
The Earth orbits the Sun, our local star. It speeds along at about 30 kilometres (19 miles) per second, taking 365.26 days (a year) to complete one orbit. As it goes, it spins on its axis like a top once every 24 hours. This makes the Sun appear to rise at dawn, pass across the sky and set at dusk, giving us day and night. The Earth is itself orbited by the Moon, which takes 27.3 days to go round it. Our closest neighbour in space, the Moon measures 3475 kilometres (2160 miles) across, about a quarter the width of Earth.
The shape of the Earth
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. The Earth measures 12,756 kilometres (7923 miles) across its Equator, its middle, and 12,714 kilometres (7897 miles) from pole to pole. The distance around the Equator is 40,075 kilometres (24,900 miles), and 40,008 kilometres (24,850 miles) from one pole around to the other and back again.
Planet Earth, as seen from space
Earth is the only world where liquid water is known to exist (although there is now strong evidence of it on Mars). Oceans occupy about 71% of its surface. Water is also present as droplets or ice particles that make up the clouds, as vapour in the atmosphere and as ice in polar areas or glaciers.
Liquid water is essential for the existence of life on Earth, unique (as far as we know) for any world in the Solar System. Its distance from the Sun—neither too close nor too far—produces exactly the right temperature range. The atmosphere traps enough of the Sun’s energy to avoid temperature extremes. It also screens the Sun's harmful rays and acts as a shield against bombardment by meteoroids.
The Earth's land areas are continually sculpted by the weather and moving water or ice. In contrast to the barren landscapes of the other rocky planets, much of Earth’s is covered by vegetation, including forest, scrub and grassland. Different climates determine the types of plants and animals that live in different places. Large areas show the important influence of humans: for example, farmland, roads and cities.
Consultant: Ian Fairchild