The history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation to the present day during the last 4.6 billion years. Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's past. The Earth is approximately one third of the age of the universe. Immense geological and biological changes have occurred during that time span.
A rare characteristic of our planet is its large natural satellite, the Moon. During the Apollo program, rocks from the Moon's surface were brought back to Earth. Radiometric dating of these rocks has shown the Moon to be 4527 Â± 10 million years old, about 30 to 55 million years younger than other bodies in the solar system. Another special feature is the relatively low density of the Moon, which must mean it does not have a large metallic core, like all other terrestrial bodies in the solar system. In fact, the Moon has a bulk composition closely resembling the Earth's mantle and crust together, without the Earth's core. This has led to the giant impact hypothesis, the idea that the Moon was formed during a giant impact of the proto-Earth with another protoplanet. The Moon formed by accretion of the material blown off the mantles of the proto-Earth and impactor.