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Transcript
The Sea Floor CH 2 pg 19 Geosphere • Geological processes influenced terrestrial and marine environments • Earth is broken into layers.. – Crust – Mantle – Core (inner/outer) Geological Layers of Earth • Crust - 1% Earth’s mass thinnest layer –Continental »Granite, less dense, floats on top oceanic – Oceanic »Basalt, dense, thinner than continental Lithosphere is part of the upper mantle • Mantle - layers beneath the crust –Lithosphere (broken into plates; tectonic) –Asthenosphere (plates float on top) »“Silly putty” »Heated and becomes less dense so material rises then as it cools material sinks creating circulating currents called convection currents »Causes plates to move Geological Layers of Earth • Core - innermost layer –Outer core »Dense liquid »Moves counter clockwise thought to create magnetic field –Inner core »Solid due to pressure »Iron and Nickel Oceans • 71% of Planet • Regulate climate and atmosphere Geography of the Ocean Basin • 2/3 of the earth’s land area in the Northern Hemisphere • The Southern Hemisphere – 80% of the ocean Five Large Basins • Pacific Ocean • deepest (approx. 14000 ft) and the largest • narrowing • Atlantic Ocean • Slowly getting bigger • Indian Ocean • Arctic Ocean • Southern Ocean • Difference between ocean and sea? The Origin and Structure of the Ocean Basins • (1912) Continental Drift Theory – All the continents had once been joined in a single “supercontinent” called Pangea – Approx 180 m.y.a. • (1950s and 1960s) Plate tectonics – Plates did drift lead to the discovery of the Mid-Ocean Ridge Evidence • • • • Pieces of a puzzle Matching sequences of rock & mountains Distribution of organisms Magnetic fields – Igneous rock – Magnetite and iron • The Mid-Ocean Ridge – System of volcanic mounts that encircles the globe – Largest geological feature on earth – Submarine mountains can break the surface of the water to form islands (ex. Iceland) – Eastern – Pacific Ridge (Subduction) Subduction vs Divergent Creation of the Sea Floor • Pieces of oceanic crust separate mid-ocean ridges by creating cracks called rifts. – Rifts release the pressure on the mantle – Reduced pressure allows hot mantle material to rise up through the rift. • • • • The magma pushes up around the rift It cools as it enters the surrounding water Creating a ridge Atlantic Ocean getting larger (Divergent) Creating New Seafloor • Repeating process makes the seafloor move away from the mid-ocean ridge • Mid-ocean ridge form the edges of continents • As the plates move the continent is carried with it (2.5 ~ 7cm/year) • Seafloor younger closest to the ridge Aleutian Islands pg 28 •Trenches curve due to Earth’s spherical shape •Volcanic islands follow trenches •Island Arcs Hot Spots pg 36 • Hawaiian Islands (plate movement) vs Aleutian Islands (subduction) • Hawaiian Islands are formed as a result of the movement of plate over a “hot spot” – Magma oozes from the thinner oceanic crust – Cools and creates a seamount – Eventually breaks the surface – Southern islands are younger Continental Volcanoes pg23 • Collision between ocean and continental plates result in volcanoes • Continent vs Continent – Himilayas & Great Smokey Mountains Transform Boundaries • Shear boundary – Plates that slide past each other – Friction prevents the plates from sliding smoothly – They lock up and stress builds up until the plates break free – Cause an earthquake – San Andres Fault (pg 29) The Ocean Floor • Sea floor is dominated by plate tectonics • Sea floor is divided into two main regions; – Continental margin – Deep-sea floor Continental Margins • Region between the continental crust and oceanic crust – Continental Shelf – Continental Slope – Continental Rise Continental Shelf • Shallow makes up 8% of the ocean’s surface area • 400-600 ft deep • Rich in life ends at the shelf break • Continental crust covered in sea water Continental Slope • Exact edge of the continent • Starts at the shelf break • Descends to the deep-sea Continental Rise • Sediment forms at the base of the continental slope • Deep-Ocean Basins – 10,000 – 16,500 ft deep – abyssal plain • Mariana Trench – West Pacific – Depth of 36,163ft (7 miles) Hydrothermal Vents • • • • • Fractures in crust water seeps down Heated water pushes its way up Creating a hydrothermal vent Temp ranging from (50 – 550o) The water contains minerals and sulfides • As the water cools the minerals solidify and deposit themselves around the vents creating chimneys, commonly called black smokers. • Tallest chimney so far rises 200 ft above sea floor