When we pose the question “What do we want to know about the Earth?”, the answer is “Everything!” We are demanding, we must be demanding. Our life, and the very survival of our species, depends on our understanding of the Earth. As long as we do not know when earthquakes will happen, when volcanoes will erupt, and how water circulates or energy is stored or minerals are concentrated, our life is a matter of chance. Fortunately, we are curious creatures, and our curiousity leads us to observe, measure, and interpret our surroundings.