The quantitative processes of eruptive development of planets into comets and other small bodies is studied from the Physical and Orbital evolution of these minor bodies. The escape of comets (and of their products of decay) into interstellar space has been of the order of 1030 to 1031 during the lifetime of the solar system. The mean density of the planets and of their large satellites, and their specific rotational energy, serve as independent checks of the amount of lost material. As far back as 1955 and 1962, the eruption theory has predicted the high volcanic activity on Venus and Mars and on some satellites, that was actually discovered by Mariner 10 and Venus 9-10. Interstellar molecules confirm that ejection of cometary gases is widespread in the Galaxy. Six new bright short-period comets discovered in 1975 provide direct evidence for comet formation in the system of Jupiter in its 1961-1969 period of high activity. Brought together, these facts prove that planetary bodies began their existence at stellar temperatures. They cooled down from the surface, forming crusts of rocky and icy materials, that have initiated a long period of eruptive evolution, characterized by numerous cataclysms with the ejection of tremendous amounts of gas and dust, separated by more quiescent phases, like the present state of the earth. Comets, asteroids, meteoritic and meteoric material bear witness for the explosive processes on planetary bodies.