Marine geology or geological oceanography involves geophysical, geochemical, sedimentological and paleontological investigations of the ocean floor and coastal margins. Marine geology has strong ties to physical oceanography.
Marine geological studies were of extreme importance in providing the critical evidence for sea floor spreading and plate tectonics in the years following World War II. The deep ocean floor is the last essentially unexplored frontier and detailed mapping in support of both military (submarine) objectives and economic (petroleum and metal mining) objectives drives the research.
The Ring of Fire around the Pacific Ocean with its attendant intense volcanism and seismic activity poses a major threat for disastrous earthquakes, tsunamis and volcanic eruptions. Any early warning systems for these disastrous events will require a more detailed understanding of marine geology of coastal and island arc environments.
The discovery and continued study of mid-ocean rift zone volcanism and hydrothermal vents, first in the Red Sea and later along the East Pacific Rise and the Mid-Atlantic Ridge systems were and continue to be important areas of marine geological research. The extremophile organisms discovered living within and adjacent to those hydrothermal systems have had a pronounced impact on our understanding of life on Earth and potentially the origin of life within such an environment.
Oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They also are the deepest parts of the ocean floor.
The Mariana Trench (or Marianas Trench) is the deepest known submarine trench, and the deepest location in the Earth's crust itself. A subduction zone where the Pacific Plate is being subducted under the Philippine Sea Plate. The bottom of the trench is further below sea level than Mount Everest is above sea level.
See also 
- Bathymetric chart
- Hawaiian-Emperor seamount chain
- List of geologists
- List of Russian geologists
- Pelagic sediments
- Erickson, John, 1996, Marine Geology: Undersea Landforms and Life Forms, Facts on File ISBN 0-8160-3354-4
- Seibold, E. and W.H. Berger, 1994, The Sea Floor: An Introduction to Marine Geology, Springer-Verlag ISBN 0-387-56884-0
- Soundwaves Coastal Science & Research News from Across the USGS
- Marine Geology and Geophysics - NOAA
- Pacific Seafloor Mapping Project - USGS
- Marine Geology and Geophysics at MIT
- Ocean Drilling Program