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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 © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole World Ocean • The ocean today – 4 major ocean basins: Pacific, Atlantic, Indian and Arctic – seas and gulfs © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole 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 © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Continental Drift • Moving continents – Alfred Wegener – Pangaea, Laurasia and Gondwanaland © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole 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 © 2006 Thomson-Brooks Cole © 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 © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 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 © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole 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 © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole 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 © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole 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 © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Finding Your Way around the Sea • Maps and charts – Mercator projections – bathymetric charts – physiographic charts © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole Finding Your Way around the Sea • Reference lines – latitude – longitude – divisions of latitude and longitude © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole © 2006 Thomson-Brooks Cole 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 © 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 © 2006 Thomson-Brooks Cole