Chapter2 theseafloor-160119025500

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1. THE SEA FLOOR 2.  about 4.6 billion years old  Geology: the science that deals with the dynamics and physical history of the earth, the rocks of which it is…
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  • 1. THE SEA FLOOR
  • 2.  about 4.6 billion years old  Geology: the science that deals with the dynamics and physical history of the earth, the rocks of which it is composed, and the physical, chemical, and biological changes that the earth has undergone or is undergoing
  • 3.  In most cases we will discuss geology in terms of habitats, the places in which organisms live
  • 4.  Oceans cover 72% of the globe and 80% of that is still considered undiscovered ◦ 2/3 of the earth’s land mass is in the Northern Hemisphere, which is only 61% ocean ◦ 80% of the Southern Hemisphere is ocean
  • 5.  1. Pacific - Largest and deepest ◦ almost as large as the other 3 combined  2. Atlantic - Second largest ◦ similar to Indian in avg. depth  3. Indian - Third largest ◦ similar to Atlantic in avg. depth  4. Arctic - Smallest and shallowest
  • 6.  All four basins are connected  This connection is most obvious when the world is viewed form the south pole ◦ Fig 2.2
  • 7.  Oceanographers often speak of one world ocean  World Ocean: Refers to the continuous body of water that surrounds Antarctica as the Southern Ocean
  • 8.  The Earth and our solar system is thought to have originated about 4.6 billion years ago from clouds or clouds of dust.   Big Bang: A great cosmic explosion that is estimated to have occurred 13.7 billion years ago in which dust particles collided with each other merging into larger particles that again collided with each other eventually building up the earth and other planets
  • 9.  Density: the mass of a given volume of a substance; Mass/Volume  When the Earth was formed it was most likely molten ◦ This allowed the interior of the Earth to form based on density  Fig 2.3
  • 10.  Core: Innermost layer of the Earth that is composed mainly of iron ◦ Pressure at the core is more than a million times the pressure on the Earth’s surface ◦ Made up of a solid inner core and a liquid outer core ◦ It is thought that the swirling motions of the liquid material in the iron-rich outer core produce the earth’s magnetic field
  • 11.  Mantle: The layer outside the earth’s core ◦ most of it is thought to be solid, but very hot - near the point of melting rock ◦ much of the mantle slowly flows almost like liquid
  • 12.  Lithosphere: The fairly rigid layer of the earth’s surface composed of the crust and upper-most part of the mantle. ◦ About 100 km (60 mi) thick ◦ Means “rock sphere” ◦ Broken up into a number of plates called lithospheric plates  Lithospheric Plates: A part of the lithosphere that can contain continental crust, oceanic crust, or both
  • 13.  Asthenosphere: The denser, more plastic layer of the upper mantle on which the lithosphere floats  The distinction between the lithosphere and the asthenosphere is based on how easily the rock flows
  • 14.  Crust: The outermost layer of the earth ◦ extremely thin in comparison to the other layers of the earth ◦ Earth’s skin
  • 15.  The geological distinction between ocean and continents results from physical and chemical differences in the rock that makes up the crust
  • 16.  Oceanic crust: The earth’s crust that makes up the sea floor, generally made up of the mineral basalt ◦ Denser than continental crust ◦ Thinner than continental crust
  • 17.  Continental crust: The earth’s crust that makes up the land portions of the world, most continental rocks are made of granite ◦ Older than the oceanic crust
  • 18. There is constant geological change
  • 19.  Sir Francis Bacon ◦ noted that the coasts of the continents on opposite sides of the Atlantic fit together like pieces of a giant puzzle ◦ Evidence in coal deposits, geological formations, and fossil findings
  • 20.  Alfred Wegener ◦ German geophysicist ◦ proposed the first detailed hypothesis of continental drift in 1912 ◦ suggested that all the continents had once been a single “supercontinent” he named Pangaea  biggest obstacle was his inability to explain how this had occurred
  • 21.  Continental drift: The movement of continental masses on the surface of the earth
  • 22.  Pangaea: The single large landmass, or supercontinent, that broke up to form today’s continents (Fig 2.16a)  One giant sea called Panthalassa which is the ancestor of the modern Pacific
  • 23.  Theory of plate tectonics: The process involved in the movement of large plates on the earth’s crust
  • 24.  Mid-ocean Ridge: A continuous chain of submarine volcanic mountains that encircles the globe like the seams on a baseball ◦ The largest geological feature on earth ◦ Displaced at locations by cracks known as faults ◦ Occasionally these mountains rise so high that they break the surface to form islands such as Iceland and the Azores ◦ Earthquakes tend to cluster near the sites of ridges
  • 25.  Fault: A crack in the earth’s crust usually formed when two pieces of crust are moving past each other
  • 26.  Mid-Atlantic Ridge: a chain of submarine volcanic mountains that runs down the center of the Atlantic Ocean, closely following the curves of the opposing coastlines. ◦ The ridge forms an inverted Y in the Indian Ocean and runs up the eastern side of the Pacific ◦ The main section of ridge in the Eastern Pacific is called the East Pacific Rise.
  • 27.  Surveys of the sea floor also revealed a system of trenches  Trench: A deep depression in the sea floor ◦ especially common in the Pacific ◦ Usually many volcanoes nearby ◦ Lithosphere is destroyed
  • 28.  A trench is formed when two plates collide and one of the plates sips below the other and sinks back down into the mantle  Subduction: The downward movement of the plate into the mantle  Trenches are also known as Subduction Zones
  • 29.  The nature of the sea floor is related to the mid-ocean ridge  Sea floor rock right near the ridge is very young and the rock gets progressively older moving away from the ridge
  • 30.  Sediment: Loose material like sand and mud that settles to the bottom, layers get thicker at greater distance from the ridge
  • 31.  From time to time the earth’s magnetic field reverses direction ◦ Reversals happen every 700,000 years on average ◦ thought to be related to movements of material in the earth’s outer core  Many rocks contain tiny magnetic particles  Magnetic Anomalies: Magnetic bands or “stripes” in the sea floor running parallel to the mid-ocean ridge
  • 32.  Rifts: Cracks in the oceanic crust separating at the mid-ocean ridges  releases some of the pressure form the underlying mantle  allows hot mantle material to melt and rise up through the rift  magma pushes up the oceanic crust around the rift to form the mid-ocean ridge (Fig. 2.9)
  • 33.  Sea-floor Spreading: The entire process by which the sea floor moves away from the mid-ocean ridges to create new sea floor  Also known as spreading centers  explains crust and sediment build up, and magnetic anomalies
  • 34.  Continental margins: are the boundaries between continental crust and oceanic crust  The shallowest part of the continental margin is the continental shelf  consists of the shelf to shelf break, continental slope, continental rise to abyssal plains
  • 35.  Continental shelf  make up about 8% of the ocean’s surface area  biologically richest part of the ocean ◦ most life and best fishing ◦ composed of continental crust  The continental shelf ends at the shelf break where the slope abruptly gets steeper
  • 36.  Two types of margins  Active Margins: zones of intense geological activity, including earthquakes and volcanoes ◦ ex. South America’s western coast  Passive Margins: zones of little geological activity with flat coastal plains, wide shelves and gradual continental slopes ◦ ex. South America’s eastern coast
  • 37.  Ocean sediment holds many clues to the earth’s past  Most marine sediments are of two basic types:  lithogenous sediment: which is derived from weathering and is usually deposited near coasts  biogenous sediment: which consists of the shells and skeletons of marine animals
  • 38.  some biogenous sediment is composed of calcium carbonate (CaCO3)  This is called calcareous ooze
  • 39.  Uses the isotope C14 to age a fossil  Half-life of 5,700 C14 to tell the age of the fossil, the percentage of C12 remains constant  Can date something up to 50,000 - 60,000 years old
  • 40.  Global warming is the increase in the average temperature of the Earth’s near surface air and oceans since the mid-20th century, and its projected continuation
  • 41.  Increasing global temperature is expected to cause sea levels to rise, an increase in the intensity of extreme weather events, and significant changes to the amount and pattern of precipitation
  • 42.  Likely leading to an increase in tropical areas and increased rates of desertification, changes in agricultural yields, modification of trade routes, glacier retreats, mass species extinctions and increases in the ranges of disease vectors
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