Introduction

Knowledge of the Earth and its evolving environment is proving increasingly crucial. Scientific, economic, political, and social decisions all depend at some time or another on this knowledge, and we like to think that we know all there is to know about our planet. One may be justified in doing so today, in the 21st century, by looking back at those maps with white unexplored regions that were still prevalent at the beginning of the 20th century. Yet, in many respects, we know more about the solid surface of other planets than about our own Earth. Rovers driving on Mars for years on end, landers on far-away Titan, and now the international missions to the Moon cannot mask the fact that ocean bottom landscapes only a few kilometers from our shores are still completely unknown.