Space and Time
Size: Diameter 12,756km
Mass: 5.97x10 (exp24) kg
Composition: Iron/nickel
Mean temperature: 22°c
Distance from Sun: 150 million km
Atmosphere/weather: Mainly nitrogen with oxygen and carbon dioxide
Moon/satellites: One
Orbital length: 365.26 days
Length of day: 24 hours
Earth is the planet we call home. It is the third planet from the Sun and the fifth largest in the solar system. Earth's diameter is just a few hundred kilometres larger than that of Venus. The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees.
Earth is the only planet in the solar system known to harbour life. There are millions of different species living in almost every environment on the planet. The human population alone is over six billion. All of the things we need to survive are protected under a thin layer of atmosphere that separates us from the uninhabitable void of space.
Oceans at least 4km deep cover nearly 70 percent of Earth's surface. Fresh water exists in the liquid phase only within a narrow temperature span (0 degrees to 100 degrees Celsius). This temperature span is especially narrow when contrasted with the full range of temperatures found within the solar system. The presence and distribution of water vapour in the atmosphere is responsible for much of Earth's weather.
View of the Great Barrier Reef, off the Australian coast, from space.
Near the surface, an ocean of air that consists of 78 percent nitrogen, 21 percent oxygen and 1 percent other ingredients envelops us. This atmosphere affects Earth's long-term climate and short-term local weather. It shields us from nearly all harmful radiation coming from the Sun and protects us from meteors as well - most of which burn up before they can strike the surface. Satellites have revealed that the upper atmosphere actually swells by day and contracts by night due to solar activity.
You can watch an animation from NASA showing the Earth rotating.
Earth's land surfaces are also in motion. For example, the North American continent continues to move west over the Pacific Ocean basin, roughly at a rate equal to the growth of our fingernails. Earthquakes result when plates grind past one another, ride up over one another, collide to make mountains, or split and separate. These movements are known as plate tectonics.
Earth is the only planet in the solar system whose name does not come from Greek or Roman mythology.
Until the 16th century, most people believed that the Sun revolved around the Earth. The astronomer Copernicus proved it was the other way round in 1514.
Find out more about how the Earth's tilt causes the seasons in our fun online feature Sunbeams and Sundials.
Images, information and videos courtesy of NASA.