Our neighbour in the space, the Moon orbits round Earth from about 4.5 billion years.
A theory asserts that it formed when an object, the same size of Mars, crashed into the still young Earth, spreading a huge cloud of detritus in the space.
Later they would joined together giving rise to the Moon.
Since it is smaller than Earth, the Moon has got less gravity and it cannot hold air or water in any way. Without an atmosphere that shelters its surface, any falling object leaves a deep mark.
The dark areas in the Moon, the so-called seas, actually are expanses of lava overflowed in consequence of the violent impact of meteorites that later solidified.
