Geology 101, Week 2 Reading Notes
Geology 101, Week 2 Reading Notes GEO 101
Popular in Dynamic Earth
Popular in Geology
This 39 page Class Notes was uploaded by Jamie Bynum on Wednesday August 31, 2016. The Class Notes belongs to GEO 101 at University of Alabama - Tuscaloosa taught by Dr. Keene in Fall 2016. Since its upload, it has received 16 views. For similar materials see Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 08/31/16
Chapter 1 • Universe: All of space and all the matter and energy within it • Cosmology: The study of the overall structure and history of the Universe • Geocentric Model: Model of the Universe where the earth is the center and everything orbits it • Heliocentric Model: Model of the Universe where the sun is the center and everything orbits it Geocentric model gained the most followers thanks to the influence of Egyptian mathematician Ptolemy During the Renaissance, thanks to Nicolaus Copernicus and Galileo Galilei, people finally realized the sun was the center • Gravity: The attractive force that one object exerts on another Sir Isaac Newton explained gravity • Matter: Substance of the Universe; it takes up space and you can feel it • Mass: The amount of matter in an object • Density: Amount of mass occupying a given volume of space • Weight: Force that acts on an object due to gravity Object with greater mass has more matter; mass of an object determines its weight depending on where it is (Moon, Earth, etc.) • Energy: The ability to do work • Star: Immense ball of incandescent gas that emits heat and light • Galaxies: Immense groups of stars that are held together by the gravity around it • Solar System: Many objects held together in a group with the sun by gravity • Planet: An object that orbits a star, is roughly spherical, and has “cleared its neighborhood of other objects” • Terrestrial Planets: Planets that consist of a shell of rock surrounding a ball of metallic iron alloy (Mercury, Venus, Earth, Mars) • Giant Planets: Consist largely of gas and ice (Jupiter, Saturn, Uranus, and Neptune) Mass of Neptune and Uranus consists mostly of solid forms of water, ammonia, and methane (Ice Giants) Mass of Jupiter and Saturn consists mostly of hydrogen and helium gas (Gas Giants) • Moon: A sizable body locked in orbit around a planet In the 1920s, unexpected observations about the nature of light from distant galaxies set astronomers on a path of discovery and ultimately led to a model of Universe formation known as the Big Bang Theory • Waves: Disturbances that transmit energy from one point to another in the form of periodic motions As each sound wave passes, air alternatively expands, then compresses • Wavelength: The distance between successive waves • Frequency: The number of waves that pass a point in a given time interval If the wavelength decreases, frequency increases The pitch of a sound depends on the frequency of the sound waves • Doppler Effect: The phenomenon in which the frequency of wave energy appears to change when a moving source of wave energy passes an observer We can represent light waves symbolically by a periodic succession of crests and troughs The color of the light you see depends on the frequency of the light waves; red light has a longer wavelength (lower frequency) than blue light If a light source moves away from you, the light you see becomes redder, as the light shifts to longer wavelengths; if the source moves towards you, the waves become shorter and the light becomes bluer; we call these changes the red shift and the blue shift In the 1920s, Edwin Hubble and other astronomers noted the location and shape of newly discovered galaxies; eventually began to note the wavelength of light produced by these galaxies; found that they display a red shift Around 1929, Hubble concluded the distant galaxies must be moving away from us; realized the whole Universe must be expanding • Expanding Universe Theory: The theory that the whole Universe must be expanding because galaxies in every direction seem to be moving away from us • Big Bang: A cataclysmic explosion that scientists suggest represents the formation of the Universe; before this event, all matter and all energy were packed into one volumeless point • Nebulae: Clouds of gas or dust in space When the Universe reached its 200 millionth birthday, it contained immense, slowly swirling, dark nebulae separated by vast voids of empty space; eventually, gravity began to remold the Universe permanently All matter exerts gravitational pull on its surroundings; a nebula began to pull in surrounding gases; the gas began swirling and formed into a rotation; due to increased rotation, the nebula evolved into a disk shape Gravity collapsed the center of the nebula disk into a dense ball that got hotter and hotter and eventually formed a protostar • Protostar: A dense body of gas that is collapsing inward because of gravitational forces and that may eventually become a star First starlight occurred around 800 million years after the Big Bang; began creation of firstgeneration stars • Supernova: A shortlived, very bright object in space that results from the cataclysmic explosion marking the death of a very large star; the explosion ejects large quantities of matter into space to form new nebulae Nebulae from which the firstgeneration stars came from were made entirely of the lightest atoms Heavier elements formed during the life cycle of stars by the process of stellar nucleosynthesis • Stellar Nucleosynthesis: The production of new, larger atoms by fusion reactions in stars; the process generates more massive elements that were not produced in the Big Bang Atoms escape a star by overcoming its gravitational pull or when the star dies • Stellar Wind: The stream of atoms emitted from a star into space Some of the heaviest atoms require a supernova explosion to ever even form • Nebular Theory: The concept that planets grow out of rings of gas, dust, and ice surrounding a newborn star The disk from which our Solar System formed contained all 92 elements Materials formed divided into two classes: 1. Volatile materials are those that can exist as a gas at the Earth’s surface; in pressure and temperature of space, they remain gases until they pass the “frost line” where some condense to ice 2. Refractory materials are those that melt only at high temperatures, and they condense to form solid sootsized particles of “dust” in space As the protoSun began to form, the middle got hot and evaporated volatile materials; in surrounding rings, refractory materials were near the middle while volatile materials stayed around the outer edges Before the protoSun ignited, the material of the surrounding rings began to clump together • Planetesimals: Tiny, solid pieces of rock and metal that collect in a planetary nebula and eventually accumulate to form a planet • Protoplanet: A body that grows by the accumulation of planetesimals but has not yet become big enough to be called a planet • Differentiation: A process early in a planet’s history during which dense iron alloy melted and sank downward to form the core, leaving lessdense mantle behind • Meteorite: A piece of rock or metal alloy that fell from space and landed on Earth Chapter 1 • Earth System: The global interconnecting web of physical and biological phenomena involving the solid Earth, the hydrosphere, and the atmosphere • Magnetic Field: The region affected by the force emanating from a magnet Earth’s magnetic field is largely a dipole, meaning it has a north pole and a south pole Earth’s magnetic field deflects most—but not all—of the Sun’s solar wind Van Allen Radiation Belt traps solar wind particles as well as cosmic rays • Atmosphere: A layer of gasses that surround a planet Earth’s atmosphere contains mostly nitrogen and oxygen The density of the air and air pressure increases the closer you get to Earth’s surface due to the weight of higher up air pushing down 99% of atmospheric gases lie below 50 km; atmosphere is barely detectable at 120 km Most winds and clouds develop in the lowest atmospheric level, the troposphere The remaining atmospheric layers, in order from lowest to highest, are: the stratosphere, the mesosphere, and the thermosphere The earth is 30% land; some land is solid rock while some is sediment Most surface water is salty Earth’s surface is not flat; topography defines plains, mountains, and valleys Bathymetry (variation in elevation of the ocean floor) defines midocean ridges, abyssal plains, and deepocean trenches Iron, oxygen, silicon, and magnesium makes up 91.2% of the Earth’s mass; the remaining 88 elements make up the other 8.8% of Earth’s mass Basic categories of materials: 1. Organic Chemicals 2. Minerals 3. Glasses 4. Rocks 5. Sediments 6. Metals 7. Melts 8. Volatiles Most common minerals in Earth contain silica mixed with other elements; called silicate minerals Four rock types in Earth’s layers: 1 Granite: A felsic rock with large grains 9. Basalt: A magic rock with small grains 10. Gabbro: A mafic rock with large grains 11. Peridotite: An ultramafic rock with large grains The average density of Earth far exceeds the density of common rocks found on the surface; mass is so great the Earth must contain a large amount of metal Earth’s three layers: 1 Crust—outer layer, composed of rocks 12. Mantle—middle layer 13. Core—inner layer; very dense Geothermal gradient is the change of temperature as you go deeper into the earth Earth’s crust is only 7 km to 70 km thick (depending on where you are) Oceanic crust (crust underlying oceans) is only 7 to 10 km thick; layer of sediment on top is generally less than 1 km thick Most continental crust (crust underlying continents) is about 35 to 40 km thick; oxygen is most abundant element Earth’s mantle is 2885 km thick; made entirely of a stone called peridotite Mantle divided into upper and lower mantles; transition zone is between 400 km and 660 km deep Core is made of iron alloy; divided into outer and inner core Lithosphere contains the Earth’s crust and outermost layer of the mantle Asthenosphere is the portion of the mantle in which rock can flow Chapter 2 • Pangaea: A supercontinent that assembled at the end of the Paleozoic Era • Continental Drift: The idea that continents have moved and are still moving slowly across the Earth’s surface German meteorologist Alfred Wegener proposed the idea of Pangaea and continental drift; was rejected since he couldn’t find a cause In 1960, American geologist Harry Hess proposed seafloor spreading • Seafloor Spreading: The gradual widening of an ocean basin as new oceanic crust forms at a midocean ridge axis and then moves away from the axis • Subduction: The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate By 1968, geologists had developed a fairly complete model encompassing continental drift, seafloor spreading, and subduction; in this model, Earth’s lithosphere consists of about 20 distinct pieces, or plates, that slowly move relative to each other • Plate Tectonics: The theory that the outer layer of the Earth consists of separate plates that move with respect to one another Geologists view plate tectonics as the grand unifying theory of geology because it can successfully explain a great many geologic phenomena Once maps of coastlines were available in 1500, scholars noticed that the continents did fit together As a glacier flows, it collects sediment grains of all sizes; grains protruding from the base of the moving ice carves scratches called stritations, into the substrate; when ice melts, it leaves the sediment in a deposit called till, that buries stritations All southern continents have glacial stritations and tills; proves Pangaea existed If southern of Pangaea was at south pole, northern of Pangaea was at the equator; should see deposits of coal from jungle plant material, reefs from shallow seas of tropical areas, and salt deposits from evaporating seawater; all these thins were found to be true Fossils were found in many places; if land was connected, animals and plants could easily have moved Earth’s dipole intersects the planet at two points, known as the magnetic poles • Magnetic Declination: The angle between the direction a compass needle points at a given location and the direction of true north • Magnetic Inclination: The angle between a magnetic needle free to pivot on a horizontal axis and a horizontal plane parallel to the Earth’s surface • Paleomagnetism: The record of ancient magnetism preserved in rock Paleomagnetism can develop in many different ways Paleomagnetism Example: 1. Lava (has no crystals) starts to cool and solidify 2. Tiny crystals begin to grow 3. Thermal energy causes tiny magnetic dipole in each crystal to wobble; dipoles of magnetic specks are randomly oriented and magnetic forces they produce cancel each other out 4. Rock cools, dipoles slow down and align with Earth’s magnetic field • Paleopole: The supposed position of Earth’s magnetic pole in the past, with respect to a particular continent • Apparent PolarWander Path: A path on the globe along which a magnetic pole appears to have wandered over time; in fact, the continents drift, while the magnetic pole stays the same Echo sounding (sonar) works on the same principle that bats use to navigate; sound pulse is emitted from a ship and travels to the sea floor; bounces off the sea floor and returns to the ship Sonar is used to measure the depth of the sea floor Several Important Features of the Ocean Floor: 1 MidOcean Ridges: Underwater “mountains” 5. Abyssal Plains: Broad, flat regions 6. DeepOcean Trenches: Elongated troughs 7. Seamount Chains: Isolated submarine mountains 8. Fracture Zones: Narrow bands of vertical cracks Discoveries of important characteristics of the seafloor crust led geologists to realize that oceanic crust differs from continental crust Bathymetric features of the ocean floor that provide clues to the origin of the crust: 1 Layer of clay sediment and tiny shells of dead plankton too thin to be there all of Earth’s history 9. Oceanic crust is different from continental crust 10. Heat flow is not the same everywhere in the oceans 11. Earthquakes define distinct belts Henry Hess proposed seafloor spreading • SeaFloor Spreading: The gradual widening of an ocean basin as new oceanic crust forms at a midocean ridge axis and then moves away from the axis Hess also theorized that old oceanic floor sank back down in deepocean trenches Magnetic field is measured in two parts: Earth’s dipole produced by the outer core and magnetism produced by near surface rocks • Magnetic Anomally: The difference between the expected strength of the Earth’s magnetic field at a certain location and the actual measured strength of the field at that location Positive anomalies are places where the field strength is stronger than expected; negative anomalies are places where the field is weaker than expected • Marine Magnetic Anomalies: The difference between the expected strength of the Earth’s magnetic field at a certain location on the ocean floor and the actual measured strength of the magnetic field at that location Marine magnetic anomalies are in distinctive, alternating bands of positive and negative • Magnetic Reversal: The change of the Earth’s magnetic polarity; when a reversal occurs, the field flips from normal to reverse polarity, or vice versa By noting a rock’s magnetic orientation and how old the rock is, geologists can make a time table of magnetic reversals A research drilling team called the “Glomar Challenger” discovered that sediment was progressively thicker the farther away from the axis of the MidAtlantic Ridge In the 1960s and 1970s, new studies defined the meaning of a plate, defined the types of plate boundaries, constrained plate motions to earthquakes and volcanoes, showed how plate interactions can explain mountain belts and seamount chains, and outlined the history of past plate motions • Lithosphere Plates: Many distinct pieces of the lithosphere separated from one another by breaks • Plate Boundaries: The borders between lithosphere plates Because of plate tectonics, the map of Earth’s surface constantly changes By looking at a map of earthquake locations, geologists can find plate boundaries • Active Margin: A continental margin that coincides with a plate boundary • Passive Margin: A continental margin that is not a plate boundary • Divergent Boundary: A boundary at which two lithosphere plates move apart from each other; they are marked by midocean ridges • Convergent Boundary: A boundary at which two plates move toward each other so that one plate sinks (subducts) beneath the other; only oceanic lithosphere can subduct • Transform Boundary: A boundary at which one plate slips past another laterally At a divergent plate, new oceanic lithosphere forms as the plates spread apart As seafloor spreading takes place, hot asthenosphere rises beneath the ridge and begins to melt, and molten rock (magma) begins to form Magma rises to either solidify as walllike sheets called dikes or spills out of underwater volcanoes to form blobs called pillows • Black Smokers: Clouds of suspended materials formed where hot water spews out of a vent along a midocean ridge; the dissolved sulfide components of the hot water instantly precipitate when the water mixes with seawater and cools As soon as it forms, new oceanic crust moves away from the ridge axis, causing more magma to rise • Subduction: The process by which one oceanic plate bends and sinks down into the asthenosphere beneath the other plate Once oceanic lithosphere has aged at least 10 million years, it becomes more dense and thus can sink if given the opportunity The subjecting plate grinds along the remaining plate, causing large earthquakes • WatadiBenioff Zone: A sloping band of seismicity defined by intermediate and deepfocus earthquakes that occur in the downgoing slab of convergent plate boundary • Accretionary Prism: A wedgeshaped mass of sediment and rock scraped off the top of a downing plate and accreted onto the overriding plate at a convergent plate margin • Volcanic Arc: A curving chain of active volcanoes formed adjacent to a convergent plate boundary If the volcanic arc forms where an oceanic plate subducts beneath continental lithosphere, the resulting chain of volcanoes grows on the continent and forms a continental volcanic arc; if the volcanic arc grows where one oceanic plate subducts beneath another oceanic plate, the resulting volcanoes form a chain of islands known as a volcanic island arc Midocean ridges are not long, uninterrupted lines, but rather consist of short segment that appear to be offset laterally from each other by narrow belts • Fracture Zone: A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to midocean ridges, and the actively slipping part of a fracture zone is a transform fault • Triple Junction: A point where three lithosphere plate boundaries intersect • HotSpot Volcano: An isolated volcano not caused by movement at a plate boundary, but rather the melting of a mantle plume • Mantle Plume: A column of very hot rock rising up through the mantle • HotSpot Track: A chain of nowdead volcanoes transported off the hot spot by the movement of a lithosphere plate • Rifting: When a continent splits and separates into two continents • Collision: The process of two buoyant pieces of lithosphere converging and squashing together • Continental Rift: A linear belt along which continental lithosphere stretches and pulls apart Nearer the surface of the continent, stretching causes the rock to break and faults to form As continental lithosphere thins, hot asthenosphere rises beneath the rift and starts to melt; eruption of the molten rock produces volcanoes along the rift If rifting continues for a long enough time, the continent breaks into two, a new midocean ridge forms, and seafloor spreading begins Collision is the process in which two buoyant pieces of lithosphere converge and squeeze together At first, scientists thought plate tectonics was caused by the plates simply floating on the asthenosphere Convection is involved in plate motions because plates where deeper, hotter asthenosphere is rising and places where shallower, colder asthenosphere is sinking causing plates to speed up or slow down • RidgePush Force: A process in which gravity causes the elevated lithosphere at a midocean ridge axis to push on the lithosphere that lies farther from the axis, making it move away • SlabPull Force: The force that downing plates (or slabs) apply to oceanic lithosphere at a convergent margin • Relative Plate Velocity: The movement of one lithosphere plate with respect to another • Absolute Plate Velocity: The movement of a plate relative to a fixed point in the mantle • Global Positioning System (GPS): A satellite system people can use to measure rates of movement of the Earth’s crust relative to one another, or simply to locate their position on Earth’s surface Chapter Summary Alfred Wegner proposed the continents had once been joined together to form a single huge supercontinent (Pangaea) and had subsequently drifted apart; this idea is the continental drift hypothesis Wegner drew from several different sources of data to support his hypothesis: 1 The correlation of the coastlines 12. The distribution of late Paleozoic glaciers 13. The distribution of late Paleozoic climate belts 14. The distribution of fossil species 15. Correlation of distinct rock assemblages now on opposite sides of the ocean Rocks retain a record of the Earth’s magnetic field that existed at the time the rocks formed; this record is called paleomagnetism; by measuring paleomagnetism in successive older rocks, geologists discovered apparent polarwander paths Apparent polarwander paths are different for different continents, because continents move with respect to each other, while the Earth’s magnetic poles remain roughly fixed Around 1960, Harry Hess proposed the hypothesis of seafloor spreading; according to this hypothesis, new sea floor forms at midocean ridges, then spreads symmetrically away from the ridge axis; eventually, the ocean floor sinks back into the mantle at deepocean trenches Geologists documented that the Earth’s magnetic field reverses polarity every now and then; the record of reversals is called the magneticreversal chronology A proof of seafloor spreading came from the interpretation of marine magnetic anomalies and from drilling studies which prove that sea floor gets progressively older away from a mid ocean ridge The lithosphere is broken into discreet plates that move relative to each other; continental drift and seafloor spreading are manifestations of plate movement Most earthquakes and volcanoes occur along plate boundaries; the interiors of plates remain relatively rigid and intact There are three types of plate boundaries: divergent, convergent, and transform; they are distinguished from each other by the movement the plate on one side of the boundary makes relative to the plate on the other side Divergent boundaries are marked by midocean ridges; at divergent boundaries, seafloor spreading produces new oceanic lithosphere Convergent boundaries are marked by deepocean trenches and volcanic arcs; at convergent boundaries, oceanic lithosphere subducts beneath an overriding plate Transform boundaries are marked by large faults at which one plate slides sideways past another; no new plate forms and no old plate is consumed at a transform boundary Triple junctions are points where three plate boundaries intersect Hot spots are places where volcanism occurs at an isolated volcano; as a plate moves over the hot spot, the volcano moves off and dies, and a new volcano forms over the hot spot; hot spot may be caused by mantle plumes A large continent can split into two smaller ones by the process of rifting; during rifting, continental lithosphere stretches and thins; if it finally breaks apart, a new midocean ridge forms and seafloor spreading begins Convergent plate boundaries cease to exist when a buoyant piece of crust (a continent or an island arc) moves into the subduction zone; when that happens, collusion occurs Ridgepush force and slabpull force contribute to driving plate motions; plates move at a rate of about 1 to 15 cm per year; modern satellite measurements can detect these motions
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