* Radiometric dating of lunar samples: Analysis of rocks and dust brought back from the Moon by Apollo missions indicates an age of around 4.51 billion years.
* Compositional similarities and differences: The Moon's composition is similar to Earth's mantle, but with a lower abundance of volatile elements (those that evaporate easily). This suggests a violent collision was involved, likely with a Mars-sized object.
* Giant-impact hypothesis: This is the leading theory for the Moon's formation. It proposes that a Mars-sized object, known as Theia, collided with the early Earth. The impact ejected a massive amount of debris, which eventually coalesced to form the Moon.
* Lunar orbital characteristics: The Moon's orbit is tilted slightly, suggesting a non-symmetrical formation event like a giant impact.
While the giant-impact hypothesis is the most widely accepted explanation, some alternative theories exist. However, the evidence overwhelmingly supports the idea that the Moon was formed by a massive impact in the early Solar System.
