We are all familiar with cycles of water and oxygen through life, the ocean and the atmosphere. The solid Earth also cycles all the elements, from interior to exterior and back again, through volcanism, plate movements, weathering, sedimentation, and exchanges with the ocean and atmosphere. There are big questions, such as why Earth has almost exactly the right amount of water to fill the ocean basins, or how much water and carbon dioxide at the surface have changed over Earth's history.
To approach these questions requires knowledge of all of Earth's solid reservoirs and what controls their chemical compositions. FIeld programs are needed to collect the necessary samples; chemical analysis in our laboratores determine the chemical make-up of the samples; theories and models are then used to understand more quantitatively what processes are occurring and why. The aim of understanding this big process then leads to more specific programs in diverse settings around the globe-- the volcanic products of ocean ridges, convergent margins, and ocean islands, and the sedimentary time series that show changes through time.