In Leonardo's view, even the consumption and metamorphosis of natural objects resulting from the action of physical and biological forces over the course of time are forms of movement. The changes that occur in man's body over the span of a lifetime and in the Earth's body over the course of the geological eras, as well as the consumption by friction of parts of machines are the various spheres in which Leonardo investigates this universal law. The incessant transfiguration of man and nature is one of the visions most deeply rooted in the mind of Leonardo.