All About Earth
Why do we have earthquakes?
Earth is the third planet from the Sun and is the largest of the rocky planets in the Solar System, in both diameter and mass. It is located about 150 million km from the Sun between Venus and Mars.Home to the human species, it is also referred to as "The Earth", "Planet Earth", "Terra", "The World", and "The Blue Planet". It is the only planet not named after a Roman or Greek God. The name derives from old English and Germanic.It was not until the time of Copernicus in the 16th Century that it was understood that the Earth is just another planet.The Earth is the first planet known to have liquid water on the surface and is the only place in the universe that is known to harbour life.....up to now.The Earth was formed around 4.5 billion years ago and its only known natural satellite, the Moon, began orbiting it around 4 million years later. The Earth travels around the Sun at nearly 30km per second or 67,000mph. It makes one complete orbit for every 365.25 times it rotates about its axis. It is this quarter day that produces a leap year or extra day every four years.The Earth's axis of rotation is tilted 23° away from the perpendicular to its orbital plane, producing seasonal variations on the planet's surface.Ice caps of frozen water at the North and South poles are gradually receding because of the build up of carbon emissions in the atmosphere causing the overall temperature to rise in a greenhouse effect.Earth has a magnetic field that, together with a primarily nitrogen-oxygen atmosphere, protects the surface from radiation that is harmful to life. The atmosphere also serves as a shield that causes smaller meteors to burn up before they strike the surface.The Earth's atmosphere is composed of 77% nitrogen, 21% oxygen with traces of argon, carbon dioxide and water. But the atmosphere is very thin. There is no definite line between atmosphere and space, it just gradually thins out the higher you go. Although humans cannot exist over about 10,000m without oxygen. At 80km you are considered to be an astronaut.The atmosphere is coloured blue because of the light scattering abilities of water molecules and other gases. Blue light is scattered more than the other colours.At Sunrise and Sunset the sky appears red because the longer red wavelengths are more prevalent.Magnetic radiation streams from the Sun and congregates at the poles in the upper atmosphere and cause the Aurora, coloured lights that dance across the sky at extreme latitudes.Clouds in the atmosphere are caused by a build up of water molecules. Clouds can be created at ground level (fog) and can extend to a height of over 8000m in the case of cirrus clouds. The presence of life on Earth has greatly affected the composition of the atmosphere. Plant life inhales carbon dioxide from the atmosphere and emits oxygen as a by-product. Mammals on the planet inhale oxygen and emit carbon dioxide, a wonderful arrangement!It is estimated that there are 6.6 billion humans, this figure is expected to rise to 7 billion by 2013.The 29% of land mass consists of deserts, mountains, plains and plateaus. The tallest mountain is Mount Everest on the border of Nepal and China it is nearly 9,000m or 29,000ft.The surface of the Earth is made from a crust of rock 0 to 60km thick, known as the Lithosphere. Below this surface is a superheated and viscous liquid inner core. The Lithosphere essentially floats on the surface of this liquid inner core, in what are known as tectonic plates.Tectonic plates are rigid sections of the Earth's surface that move in relation to each other. It is when two or more of these plates grind together that we get Earthquakes. Collisions between the plates give rise to high mountain ranges as the surfaces are pushed up. 71% of the surface is covered by salt water oceans. The abundance of water on the Earth's surface is what