Earth

From ArticleWorld

The Earth is the fifth largest planet in our Solar System and is the only planet on which life is known to exist. The Earth is the third planet from the Sun. The Earth is estimated to have been formed approximately 4.57 billion years ago and it has one moon that orbits it. The formation of Earth to present has seen a total change in the original conditions. Many geological and biological processes have caused these changes.

Features

The surface of Earth is composed of several tectonic plates while the interior has an active thick layer of molten Earth mantle and iron core which creates a magnetic field. The presence or formation of life could itself have caused the change in the Earth's surface and resulted in the balance we see today. There is about 70% of the surface that is covered with salt water and the remainder made up of freshwater, continents and islands.

The Earth is greatly affected by its moon and this is seen mainly in the ocean's tides that have cause gradual changes in the rotation of the Earth. The presence of water is thought to be through the bombardment of the surface of the Earth by a comet early in Earth's history. Other surface changes are attributed to asteroid impacts. There is also the thought that the ice ages may have occurred due to alterations in the orbit of the planet.

Earth and the Solar System

The rotation of the Earth is completed on average in about 23 hours, 56 minutes and 4.091 seconds. This rotation is about the axis that connects the South Pole to the North Pole. The earth itself orbits the Sun every 365.2564 mean solar days. The Earth only has one natural satellite and this is the moon. This revolves around the Earth approximately every 27.32 days. When the Earth is viewed from the North Pole its motion is determined to be in an anticlockwise direction and the orbital and axial planes are not aligned precisely. The Earth has a tilt of about 23.5 degrees in the Earth-Sun plane and in the Earth-Moon plane the tilt is about 5 degrees to the Earth-Sun plane. The 23.5 degree tilt is responsible for the changes in seasons as we know it.