Earth’s infinite geological complexity fascinates us, and centuries of detailed observations and modeling can tempt us to believe that we have a full understanding of Earth’s igneous processes. Our world, however, is only one data point in the Solar System. A model that successfully predicts or explains a volcanic process on Earth, for example, may fail completely when applied to another planetary body. Such comparative planetology is therefore critical, and reveals the weaknesses in our understanding that would otherwise remain hidden: just because a model works on Earth does not mean that it truly explains a given process elsewhere using first principles. <...>

The theme of this book is the study of basaltic volcanism as a stage in planetary evolution: to use the eruption of lava from the interior of a planet as evidence of the thermal and chemical processes of the planet. All lavas extruded on a planet’s surface can provide information about events in the interior. From a petrologic point of view, however, it is the more primitive lavas, which rise to the surface of a planet with minimal changes, that can provide the most information about the interior. In general, these more primitive lavas are basalts and so in Chapter 1 our sampling has concentrated on basaltic rocks.