One theory about the origin of the Moon states it was formed from debris thrown out when a Mars-sized object collided with Earth. One fact that strongly supports this theory is that:

Question

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The similarity in composition between Moon rocks and Earth rocks, especially the depletion in elements that melt at low temperatures, supports the theory that the Moon was formed from debris resulting from a massive collision with Earth. This is because the heat of such an impact would have melted those elements, causing them to vaporize and be lost from the debris that formed the Moon.

One Theory About the Origin of the Moon States It