Earth

Earth is the third planet from the Sun and the largest rocky planet in the solar system. It is the only known place where life exists. Most of its surface is covered by water, while the remainder is solid land.

Alternative names include 'The World'. A famous photograph taken from space showing Earth rotating and blue in colour is called 'The Blue Marble'.

Rotation and time

Earth orbits the Sun once per year—known as the orbital period. At the same time, it rotates on its axis approximately once every 24 hours, which creates day and night. The axis has a tilt, which causes the seasons to change throughout the year in regions away from the equator.

Structure

Earth consists of layers: a hard crust, a hot mantle, and a core rich in iron. The movement of the crust—known as plate tectonics—causes earthquakes, volcanoes, and mountains. The core generates a magnetic field that shields part of the upper atmosphere from incoming radiation.

Atmosphere and water

Earth's atmosphere consists mainly of nitrogen and oxygen. Water exists on its surface in liquid form, affected by temperature and pressure. Small amounts of gases in the atmosphere, such as carbon dioxide, trap heat—a process called the greenhouse effect.

The Moon

Earth has one large moon. The gravitational pull of the moon affects ocean tides and also stabilizes the tilt of Earth's axis.