Mid-ocean ridges are where the oceanic crust, which covers over 60% of the Earth's surface and is renewed every 200 million years or so, is generated. They are thus features of first-order importance in the Earth system. Mid-ocean ridges were discovered some 150 years ago, and have been studied with increasing intensity and detail since then. We are now beginning to have an outline level of understanding of their structures and processes. Ridges are primarily studied by geophysicists and geologists. But chemists are interested because ridge crest hydrothermal systems exchange chemical elements between the rock of the oceanic crust and the overlying ocean waters; physical oceanographers are concerned with how ridge topography and geothermal heat influence ocean waters and currents, and biologists study the unique ecosystems that inhabit hydrothermal vents, which may hold clues to the origins of life and the nature of the ‘deep biosphere’ of microbes that live deep in crustal rocks.

This book attempts to set out an overview of the current understanding of mid-ocean ridges across most of the scientific disciplines involved. I have tried to make it reasonably comprehensive, while admitting that an encyclopaedic coverage is certainly beyond my ability. I intend the book to be suitable for a wide audience, in terms of both their level of prior knowledge and the nature of their disciplines. Thus I hope it can be used as a general introduction and reference by senior undergraduates and starting postgraduate students taking courses in, for example, geodynamics, Earth systems or oceanography, by doctoral students as a starting point for their researches, and by both academic and other professionals who may need an introduction or reference to areas outside their immediate specialties.