Did a large body hit the earth to form the moon?

Answer 1

There is growing evidence and belief among Earth scientists that there was indeed a giant impact with a large body somewhere between the size(s) of Planet Mercury and Planet Mars which struck the Earth some 4.5 billion years ago. This is commonly referred to as the "Giant Impact Hypothesis". Strong support for this theory comes from many angles. One of which is the fact that Moon rock and Earth rock is derived from the same compounds.

The commonly accepted name for the Planetary body believed to have struck and molded with Earth is "Theia". This designation was first proposed by the English geochemist Alex N. Halliday in 2000 and has since become accepted in the scientific community. According to modern theories of planet formation, Theia was part of a population of Mars-sized bodies that existed in the Solar System 4.5 billion years ago. Indeed, one of the attractive features of the giant impact hypothesis is that the formation of the Moon fits into the context of the formation of the Earth itself: during the course of its formation, the Earth is thought to have experienced dozens of collisions with such planet-sized bodies. The Moon-forming collision was only one such "giant impact" and perhaps the last.

Because of gravity, the surface of the moon and Earth have smoothed over millions of years. Theia was engulfed by the Earth, in theory, making Earth much larger than it was prior to the impact, even though large chunks fell off which ultimately formed the moon.