Karleskint Karleskint Small Small Turner Turner
Chapter 3
Chapter 3
Geology of the Ocean
Key Concepts
• The world ocean has four main basins: the
Atlantic, Pacific, Indian, and Arctic.
• Life first evolved in the ocean.
• The earth’s crust is composed of moving
plates.
• New seafloor is produced at ocean ridges
and old seafloor is removed at ocean
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.
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 worked its way to the surface, where it cooled,
World Ocean
• Ocean and the origin of life
– atmosphere formed by gases escaping from deep within the planet
– free oxygen formed oxides, oxygen did not accumulate until evolution of modern
photosynthesis
World Ocean
• The ocean today
– 4 major ocean basins:
• Pacific • Atlantic • Indian • Arctic
– Pacific Ocean - largest – Arctic Ocean - smallest
Continental Drift
• Layers of the earth
– Inner core: solid, iron- and nickel-rich – Outer core: liquid (same composition)
– Mantle: thickest layer with greatest mass, mainly magnesium-iron silicates
– Crust: thinnest and coolest, outermost – Lithosphere: crust and upper mantle
Continental Drift
• Moving continents
– Alfred Wegener
– Continents fit together like pieces of jigsaw puzzle
Continental Drift
• Forces that drive continental movement
– magma moves by 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
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
II.
Forces that drive
continental
movement
– at subduction
zones, old crust
sinks into the
Continental Drift
• Theory of plate tectonics
– lithosphere is viewed as a series of rigid plates separated by earthquake belts
– divergent plate boundaries: located at
midocean ridges where plates move apart – convergent plate boundaries: located at
trenches where plates move toward each other
– faults: regions where plates move past each other (e.g. transform faults)
Continental Drift
• Rift (Deep Sea Vent) Communities
– depend on specialized environments found at divergence zones of the ocean floor
– first discovered by Robert Ballard and J.F. Grassle in 1977, in the Galápagos Rift
Ocean Bottom
• Bathygraphic features
– Geological features similar to land: mountain ranges; canyons, valleys; great expanses
• Continental margins
– continental shelf, continental slope, and shelf break
• Submarine canyons
• Continental Rises
Continent Subsurface rock Continental rock Continental rock Continental rock Wave-cut terrace Sediment from beach erosion
River River sediment
Sediments Water-deposited sediment Coral reef, volcano, or island Stepped Art
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
Composition of the Seafloor
Composition of the Seafloor
• Hydrogenous sediments
– formed from seawater through a variety of chemical processes
– e.g. carbonates, phosphorites, manganese nodules
• Biogenous sediments
– formed from remains of living organisms – mostly particles of corals, mollusk shells,
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
Finding Your Way around the Sea
• Maps and charts
Finding Your Way around the Sea
• Reference lines
– latitude – longitude
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
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
