The Dynamic Earth (Geology for non
The Dynamic Earth (Geology for non GEOL 1104
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This 7 page Class Notes was uploaded by Gaylord O'Keefe on Monday October 26, 2015. The Class Notes belongs to GEOL 1104 at University of Oklahoma taught by Michael Engel in Fall. Since its upload, it has received 27 views. For similar materials see /class/229284/geol-1104-university-of-oklahoma in Geology at University of Oklahoma.
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Date Created: 10/26/15
Natalie Schmigle Geology Engel 20 August 2012 1 N V 4 Geology The Science of Geology a Geology the science that pursues an understanding of planet Earth i Physical Geology examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface ii Historical Geology seeks an understanding of the origin of Earth and its development through time b Some historical notes about geology i The nature of Earth has been a focus of study for centuries ii Catastrophism iii Uniformitarianism and the birth of modern geology Geologic time a Geologists are now able to assign fairly accurate dates to events in Earth history b Relative dating and the geologic time scale i Relative dating means that dates are placed in their proper sequence or order without knowing their age in years c Law of Superposition i In an undeformed sequence of sedimentary rocks each layer is older than the one above it and younger than the one beneath it ii Law of Faunal succession Fossil organisms succeed one another in a definite determinable order iii Relative vs Absolute Dating d Magnitude of geologic time i Involved vast times millions or billions ofyears ii An appreciation for the magnitude of geologic time is important because many processes are very gradual Index Fossils a Geographically widespread b Easily recognized c Restricted to a specific interval of geologic time A view of Earth a Earth is a planet that is small and selfcontained b Earth s four spheres i Hydrosphere ii Atmosphere iii Biosphere iv Solid Earth Early evolution of Earth a Origin of planet Earth 6 Ear SJ V U V i Most researchers believe that Earth and the other planets formed at essentially the same time ii Nebular hypotheses 1 Rotating cloud called the solar nebula 2 Composed of hydrogen and helium 3 Nebula began to contract about 5 billion years ago 4 Assumes a at disk shape with the protosun presun at the center 5 Inner planets begin to form from metallic and rocky substances 6 Larger outer planets began forming from fragments ofices HZOCOZ and others Formation of Earth s layered structure i Metals sank to the center ii Molten rock rose to produce a primitive crust iii Chemical segregation established the three basic divisions of Earth s interior iv Primitive atmosphere evolved from gases in Earth s interior th s internal structure Layers defined by composition i Crust ii Mantle iii Core Layers defined by physical properties i Lithosphere ii Asthenosphere iii Mesosphere iv Inner and Outer Core The face of the Earth 8 bl Earth s surface i Continents ii Oceans Continents i Mountain belts 1 Most prominent feature of continents ii The stable interior 1 Also called a craton composed of shields and stable platforms Ocean basins i Continental margins 1 Includes the continental shelf continental slope and the continental rise ii Deepocean basins 1 Abyssal plains 2 Oceanic trenches 3 Seamounts iii Oceanic ridge system 1 Most prominent topographic feature on Earth 2 Composed of igneous rock that has been fractured and uplifted 8 Rocks and the rock cycle a Basic rock types i Igneous rocks 1 Cooling and solidification of magma 2 Examples include granite and basalt ii Sedimentary rocks 1 Accumulate in layers at Earth s surface 2 Sediments are derived from weathering of preexisting rocks 3 Examples include sandstone and limestone iii Metamorphic rocks 1 Formed by quotchangingquot preexisting igneous sedimentary or other metamorphic rocks 2 Driving forces are increased heat and pressure 3 Examples include gneiss and marble b The Rock Cycle One of Earth s subsystems i The loop that involves the processes by which one rock changes to another ii Illustrates the various processes and paths as earth materials change both on the surface and inside the Earth Natalie Schmigle Engel Geology 21 August 2012 Plate Tectonics A Scientific Revolution Unfolds 1 Continental drift a An Idea Before Its Time i Alfred Wegener 1 First proposed his continental drift hypothesis in 1915 2 Published The Origin ofContinents and Oceans ii Continental drift hypothesis 1 Supercontinent called Pangaea began breaking apart about 200 million years ago 2 Continents quotdriftedquot to present positions iii Evidence used to support continental drift hypothesis 1 Fit of the continents 2 Fossil evidence 3 Rock type and structural similarities 4 Paleoclimatic evidence b The Great Debate i Objections to the continental drift hypothesis 1 Lack of a mechanism for moving continents 2 Wegener incorrectly suggested that continents broke through the ocean crust much like ice breakers cut through ice 3 Strong opposition to the hypothesis from all areas of the scientific community ii Continental drift and the scientific method 1 Wegener s hypothesis was correct in principle but contained incorrect details 2 A few scientists considered Wegener s ideas plausible and continued the search Continental drift and paleomagnetism i Renewed interest in continental drift initially came from rock magnetism ii Magnetized minerals in rocks 1 Show the direction to Earth s magnetic poles 2 Provide a means of determining their latitude of origin iii Polar wandering 1 The apparent movement of the magnetic poles illustrated in magnetized rocks indicates that the continents have moved 2 Indicates Europe was much closer to the equator when coal producing swamps existed 3 Curves for North America and Europe have similar paths but are separated by about 24 degrees oflongitude a Differences between the paths can be reconciled if the continents are placed next to one another d A scientific revolution begins 0 V i During the 1950s and 1960s technological strides permitted extensive mapping of the ocean oor ii Sea oor spreading hypotheses was proposed by Harry Hess in the early 1960s iii Geomagnetic reversals 1 Earth s magnetic field periodically reverses polarity the north magnetic pole becomes the south magnetic pole and vice versa 2 Dates when the polarity of Earth s magnetism changed were determined from lava ows 3 Geomagnetic reversals are recorded in the ocean crust 4 In 1963 Vine and Matthews tied the discovery of magnetic stripes in the ocean crust near ridges to Hess s concept of sea oor spreading 5 Paleomagnetism was the most convincing evidence set forth to support the concepts of continental drift and sea oor spreading e Plate tectonics The new paradigm CD i Earth s major plates 1 Associated with Earth s strong rigid outer layer a Known as the lithosphere b Consists of uppermost mantle and overlying crust c Overlies a weaker region in the mantle called the asthenosphere 2 Seven major lithospheric plates 3 Plates are in motion and continually changing in shape and size 4 Largest plate is the Pacific plate 5 Several plates include an entire continent plus a large area of sea oor 6 Plates move relative to each other at a very slow but continuous rate a About 5 centimeters per year b Cooler denser slabs ofoceanic lithosphere descend into the mantle ii Plate boundaries 1 Interactions among individual plates occur along their boundaries a Divergent plate boundaries constructive margins b Convergent plate boundaries destructivemargins c Transform fault boundaries conservative margins 2 Each plate is bounded by a combination of the three types of boundaries 3 New plate boundaries can be created in response to changing forces Divergent plate boundaries i Most are located along the crests of oceanic ridges ii Oceanic ridges and sea oor spreading 1 Along welldeveloped divergent plate boundaries the sea oor is elevated forming oceanic ridges 2 Sea oor spreading occurs along the oceanic ridge system iii Spreading rates and ridge topography 1 Ridge systems eXhibit topographic differences 2 These differences are controlled by spreading rates iv Continental rifting 1 Splits landmasses into two or more smaller segments along a continental rift 2 Examples include the East African rift valleys and the Rhine Valley in northern Europe 3 Produced by extensional forces acting on lithospheric plates g Convergent plate boundaries i Older portions of oceanic plates are returned to the mantle in these destructive plate margins 1 Surface expression of the descending plate is an ocean trench 2 Also called subduction zones 3 Average angle of subduction 45 degrees ii Types of convergent boundaries 1 Oceaniccontinental convergence a Denser oceanic slab sinks into the asthenosphere b Along the descending plate partial melting of mantle rock generates magma c Resulting volcanic mountain chain is called a continental volcanic arc 2 Oceanicoceanic convergence a When two oceanic slabs converge one descends beneath the other b Often forms volcanoes on the ocean oor c If the volcanoes emerge as islands a volcanic island arc is formed 3 Continentalcontinental convergence a Continued subduction can bring two continents together b Less dense buoyant continental lithosphere does not subduct c Resulting collision between two continental blocks produces mountains h Transform fault boundaries i Plates slide past one another and no new lithosphere is created or destroyed ii Transform faults 1 Most join two segments ofa midocean ridge along breaks in the oceanic crust known as fracture zones 2 Afew cut through continental crust Testing the plate tectonics model i Evidence from ocean drilling 1 Some of the most convincing evidence confirming sea oor spreading has come from drilling directly into ocean oor sediment a Age of deepest sediments b Thickness of ocean oor sediments verifies sea oor spreading ii Hot spots and mantle plumes 1 Caused by rising plumes of mantle material 2 Volcanoes can form over them 3 Mantle plumes a Longlived structures h 1 V Q b Some originate at great depth perhaps at the mantlecore boundary Measuring plate motion i Paleomagnetism and plate motions 1 Paleomagnetism stored in rocks on the ocean oor provides a method for determining plate motions 2 Both the direction and rate of sea oor spreading can be established ii Measuring plate velocities from space 1 Accomplished by establishing exact locations on oppoite sides ofa plate boundary and measuring relative motions 2 Two methods are used a Very Long Baseline Interferometry VLBI b Global Positioning System GPS What drives plate motions i Researches agree that convective ow in the mantle is the basic driving force of plate tectonics ii Forces that drive plate motions 1 Slabpull 2 Ridgepush 3 Slab suction iii Models ofplatemantle convection 1 Any model must be consistent with observed physical and chemical properties of the mantle 2 Models a Layering at 660 kilometers b Wholemantle convection c Deeplayer model Importance ofplate tectonics i The theory provides explanations for 1 Earth s major surface processes 2 The geologic distribution of earthquakes volcanoes and mountains 3 The distribution of ancient organisms and mineral deposits
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