Earth is the third planet in the planetary system in terms of distance from the Sun, and the fifth largest. It is also the major of its planetary system's terrestrial planets, making it the biggest solid body in the solar system, and it is the only place in the world known to humans to support life. It is also the densest planet in the solar system. The extensively accepted scientific theory states that the Earth was formed around 4.57 billion years ago and its natural satellite, the Moon, was orbiting it shortly subsequently, around 4.53 billion years ago.
Since it shaped, the Earth has altered through geological and biological processes that have secreted traces of the original conditions. The outer surface is divided into several tectonic plates that steadily migrate across the surface over geologic time spans. The interior of the earth remains active, with a thick layer of convecting up till now solid Earth covering and an iron core that generates a fascinating field. Its atmospheric conditions have been significantly altered by the presence of life forms, which create an ecological balance that modifies the surface circumstances. About 71% of the surface is covered in salt-water oceans, and the remainder consists of continents and islands.