1. Understanding Earth Fourth Edition Chapter 17:
Frank Press, Raymond Siever,
John Grotzinger, and Thomas H. Jordan
Understanding Earth
Fourth Edition
Chapter 17:
Earth Beneath the Oceans
Copyright © 2004 by W. H. Freeman & Company

2. Marine Geology Most of the world is under water -- 71%
Plate Tectonics came about mainly from the study of marine geology

3. Major Differences between the Ocean Floor and the Surface of Continents
Continental surfaces are a source of sediment, that is they are regions where erosion and weathering prevail. Continents are ~4 by old
Ocean floors are regions where net sedimentation and volcanism prevail. Oceans are no more that 200 Myr old

5. About Oceanic Geology
Volcanism dominates near oceanic ridges and hot spots.
Sedimentation dominates elsewhere
Older volcanic crust usually has a thicker pile of overlying sediments

6. How have earth scientists learned about the depths of the world’s oceans?
HMS Challenger, 1872 throughout a 4-year voyage, used rope lines to estimate ocean depths.
Today we use echo sounders, devices that emit a pinging sound and record its return later in time. Knowing the speed of sound and the time of flight of these echoes can be used to calculate water depths.

8. How have earth scientists learned about the geology of the world’s oceans?
Submersibles-- e.g. Johnson SeaLink, Alvin -- biology, petrology
Academic Drilling- DSDP, ODP, IODP
Commercial drilling and seismic exploration for oil and gas
Swath Mapping--Beams of sound (many pings in many directions received at many stations on the underside of a vessel) -- bathymetry
seismometer stations around the world
Today we use echo sounders, devices that emit a pinging sound and record its return later in time. Knowing the speed of sound and the time of flight of these echoes can be used to calculate water depths.

12. How have earth scientists learned about the geology of the world’s oceans?
Satellites data can be used to make bathymetric maps
Satellites can access the most remote parts of the world
Satellites can detect ocean surface elevation.
Ocean height depends on waves,currents, and the underlying topography (bathymetry)

13. A “typical” oceanic bathymetric profile across two plates that are diverging …..
The Atlantic Ocean
is 5000 km across
is shallowest in the center (2500 m deep) and deeper along its flanks in the abyssal plain

15. Key Features across the Atlantic Seafloor
a continental shelf ( < 200 m water depth) that is often cut by submarine canyons
A continental slope ( > 200 m, 4 degrees dip, i.e. 70 m drop per 1 km run)
A continental rise ( m)
An abyssal plain ( m)
Seamounts - extinct underwater volcanoes
Mid-oceanic Ridges - active underwater mountain chain

18. Key Features across the Pacific Seafloor
Trenches
seamounts
guyots - flat-topped extinct marine volcanoes, flat-topped because they were once above sea-level and were eroded

21. A Great Discovery
Life does not only derive from sunlight energy!

23. Sources of Deep-Sea Sediments
Derive from
(1) the dead skeletons of foraminifera (single-cell animals) that live in the
(2) wind-borne or underwater-borne clays

25. Carbonate Compensation Depth (CCD)
Below a certain depth (CCD), the skeletons dissolve back into sea water and do not make it into the sediment!

27. Wave Action Waves in general, are created by wind
Wind velocity, area affected by winds and length of time that the wind blows are all factors that help to increase the height of a wave
Wave particle motion is circular at the surface to elliptical at the bottom
Waves that hit the coast at an angle created a longshore drift of sediments along the coast

29. Wave Action
Waves that hit the coast at an angle created a longshore drift of sediments along the coast

31. Tides
Tides can leave you high and dry, twice a day and can be intensified by local bathymetry
The largest tides occur when the sun and moon are aligned (spring tides) and the smallest are when the sun and moon are aligned at right angles to each other.

34. “The Beginning for a few is the End for Many”