https://en.wikipedia.org/wiki/Giant-impact_hypothesis Following the suggestion, that the Moon was formed 4.5 bya by a large impact of a heavenly body labeled Theia and one labeled Young Earth, I wondered if maybe that's the reason we have continents? Just like there are visible differences between the Earth's ocean floors and its continents, there are similar differences on the surface of the Moon, dark and light patches, the dark patches usually being called "maria", from 'mare' for ocean in Latin, e.g. Mare Tranquillitatis, where Apollo 11 landed. Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image! Also, the backside of the moon has almost no dark spots. Please Register or Log in to view the hidden image! So, if the Moon was formed after an ancient impact between Young Earth and this Theia, would the dark patches on the Moon and the Earth's ocean floors be the original composition of Young Earth, and the light patches on the Moon and the Earth's continents be the original composition of Theia? (Or maybe vice versa, I don't know.) The side of the Moon with the dark patches always angle that side towards the Earth, so after an ancient impact, material from both bodies mixed together in the new Earth to form continents and ocean floors (with are then subject to plate tectonics), and in the Moon to form the light and dark patches. Anyway, just something to get out of my head after watching a couple of astronomy documentaries. A simple thing could answer this: Do other bodies in the Solar System have similar continent-like structures? Which may or may not be the result of similar ancient impacts and mix of planetary rocky materials, distinct from each other? Using the Lunar samples from the Apollo missions, is there a similar chemical structure between samples from the dark patches and samples from ocean floors, and conversely between samples from light patches and continents? These two types being distinct from each other.