Geology of the Oceans

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Chapter 3

• Geology of the Oceans

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Key Concepts

• The world ocean has four main basins the
  Atlantic, Pacific, Indian, and Arctic.
• Life first evolved in the ocean.
• The earths crust is composed of moving plates.
• New seafloor is produced at ocean ridges and old
  seafloor is removed at ocean trenches.

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Key Concepts

• The ocean floor has topographical features
  similar to those found on continents.
• The seafloor is composed of sediments derived
  from living as well as nonliving sources.
• Latitude and longitude determinations are
  particularly necessary for precisely locating
  positions in the open sea, where there are no
  features at the surface.

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World Ocean

• Primitive earth and formation of the ocean
• early earth thought to be composed of silicon
  compounds, iron, magnesium oxide, and other
  elements
• gradually, the earth heated, causing melting and
  separation of elements
• water vapor locked within minerals released to
  the surface, where it cooled, condensed, and
  formed the ocean

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World Ocean

• Ocean and the origin of life
• atmosphere formed by gases escaping from the
  planet
• no accumulation of oxygen until evolution of
  photosynthesisfree oxygen forms oxides
• Stanley Millers apparatus

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World Ocean

• The ocean today
• 4 major ocean basins Pacific, Atlantic, Indian
  and Arctic
• seas and gulfs

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Continental Drift

• Layers of the earth
• solid inner coreiron- and nickel-rich
• liquid outer core (same composition)
• mantlethickest layer with greatest mass, mainly
  magnesium-iron silicates
• crustthinnest and coolest, outermost

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Continental Drift

• Moving continents
• Alfred Wegener
• Pangaea, Laurasia and Gondwanaland

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Continental Drift

• Forces that drive continental movement
• magma convection currents
• midocean ridges form along cracks where magma
  breaks through the crust
• at subduction zones, old crust sinks into the
  mantle where it is recycled
• seafloor spreading causes continental drift

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Continental Drift

• Evidence for continental drift
• fit of continental boundaries
• earthquakes
• seafloor temperatures highest near ridges
• age of crust, as determined by samples drilled
  from the ocean bottom, increases with distance
  from a ridge

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Continental Drift

• Theory of plate tectonics
• lithosphere is viewed as a series of rigid plates
  separated by earthquake belts
• divergent plate boundariesmidocean ridges where
  plates move apart
• convergent plate boundariestrenches where plates
  move toward each other
• faultsregions where plates move past each other
  (e.g. transform faults)
• rift zoneswhere lithosphere splits

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Continental Drift

• Rift communities
• depend on specialized environments found at
  divergence zones of the ocean floor
• first was discovered by Robert Ballard and J.F.
  Grassle in 1977, in the Galápagos Rift
• primary producers are chemosynthetic bacteria

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Ocean Bottom

• Continental margins
• continental shelf, continental slope, and shelf
  break
• submarine canyons and turbidity currents
• continental rises
• shaping the continental shelves
• glaciers
• sediments

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Ocean Bottom

• Ocean basin
• abyssal plains and hills
• seamounts
• ridges and rises
• trenches and island arcs
• Life on the ocean floor
• continental shelves are highly productive
• life on the abyssal plains is not abundant owing
  to the absence of sunlight

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Composition of the Seafloor

• Sedimentloose particles of inorganic and organic
  material

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Composition of the Seafloor

• Hydrogenous sediments
• formed from seawater through a variety of
  chemical processes
• e.g. carbonates, phosphorites
• Biogenous sediments
• formed from living organisms
• mostly particles of corals, mollusc shells,
  shells of planktonic organisms

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Composition of the Seafloor

• Terrigenous sediments
• produced from continental rocks by the actions of
  wind, water, freezing, thawing
• e.g. mud (clay silt)
• Cosmogenous sediments
• formed from iron-rich particles from outer space
  which land in the ocean and sink to the bottom

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Finding Your Way around the Sea

• Maps and charts
• Mercator projections
• bathymetric charts
• physiographic charts

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Finding Your Way around the Sea

• Reference lines
• latitude
• longitude
• divisions of latitude and longitude

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Finding Your Way around the Sea

• Navigating the ocean
• principles of navigation
• a sextant was used to determine latitude based on
  the angle of the North Star with reference to the
  horizon
• longitude determined using chronometer

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Finding Your Way around the Sea

• Navigating the ocean
• global positioning system (GPS)
• utilizes a system of satellites to determine
  position
• GPS measures the time needed to receive a signal
  from 3 satellites, and calculates position

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