© 2006 Thomson-Brooks Cole Chapter 3 Geology of the Oceans
© 2006 Thomson-Brooks Cole 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 trenches.
© 2006 Thomson-Brooks Cole 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.
© 2006 Thomson-Brooks Cole 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
© 2006 Thomson-Brooks Cole World Ocean Ocean and the origin of life –atmosphere formed by gases escaping from the planet –no accumulation of oxygen until evolution of photosynthesis—free oxygen forms oxides –Stanley Miller’s 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 core—iron- and nickel-rich –liquid outer core (same composition) –mantle—thickest layer with greatest mass, mainly magnesium-iron silicates –crust—thinnest 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
© 2006 Thomson-Brooks Cole
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
© 2006 Thomson-Brooks Cole
Continental Drift Theory of plate tectonics –lithosphere is viewed as a series of rigid plates separated by earthquake belts –divergent plate boundaries—midocean ridges where plates move apart –convergent plate boundaries—trenches where plates move toward each other –faults—regions where plates move past each other (e.g. transform faults) –rift zones—where lithosphere splits
© 2006 Thomson-Brooks Cole 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
© 2006 Thomson-Brooks Cole 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 Sediment—loose particles of inorganic and organic material
© 2006 Thomson-Brooks Cole 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
© 2006 Thomson-Brooks Cole
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
© 2006 Thomson-Brooks Cole