Source: Amaterasu cave
crop, Wikipedia

At the beginning the universe was immersed in a beaten and shapeless kind of matter (chaos), sunk in silence. Later there were sounds indicating the movement of particles. With this movement, the light and the lightest particles rose but the particles were not as fast as the light and could not go higher. Thus, the light was at the top of the Universe, and below it, the particles formed first the clouds and then Heaven,which was to be called Takamagahara (高天原, “High Plain of Heaven”). The rest of the particles that had not risen formed a huge mass, dense and dark, to be called Earth.