Volcanologists and the geologic past

Were volcanologists to be asked why they study active volcanoes, they would list many reasons: to understand their dynamics, to use them as windows into the earth, to warn of hazards, to provide nearly real-time information on rates of various physical and chemical processes, and many others. Near the bottom of the list would be "to understand the Earth's past." Generally, that task has been left to other corners of the earth sciences, and volcanologists have kept their sights on the present or near present without worrying much about what happened millions of years ago. But much can be gained from applying a volcanologic perspective to the interpretation of old rocks, and this gain enhances our understanding of both the past and the present.