The cosmic egg, world egg or mundane egg is a mythological motif found in the cosmogonies of many cultures and civilizations, including in Proto-Indo-European mythology. Typically, there is an egg which, upon "hatching", either gives rise to the universe itself or gives rise to a primordial being who, in turn, creates the universe. The egg is sometimes lain on the primordial waters of the Earth. Typically, the upper half of the egg, or its outer shell, becomes the heaven (firmament) and the lower half, or the inner yolk, becomes the Earth. The motif likely stems from simple elements of an egg, including its ability to offer nourishment and give rise to new life, as is reflected by the Latin proverb omne vivum ex ovo.