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of Definition a glacier o Large mass of slowly moving ice o Ice sheets are glaciers that cover large areas of continents o Form above the snowline, confined to high altitudes o Higher part of glacier gets thicker with snow each year o Ice flows downhill under its own weight, combination of plastic deformation, some melting at the base o Abalation- balance between accumulation of snow and melting snow, if net accumulation is larger than net abalation the glacier grows and pushes its front downhill. Greenhouse gases o Keep earth's temp warm o Increased CO2 in last 100 years from burning coal, natural gas, and petroleum o Clearing forests helps increase CO2 o Long term effect- greenhouse gases remain in atmosphere for decades Location of deserts and causes of aridity o Deserts are defined by a low amount of precipitation and cover 19% of land surface o Deserts are found in both cold and hot environments o Mechanical weathering is dominant--sparse vegetation o Water is the main weathering agent with wind o Nile, uadi, arroyos Beach erosion o Sloping portion of the coast composed of sediments and moved by waves, tides, and currents o Sediment comes from rivers and wave erosion on cliffs o Human impact--river damming reduces sediment supply- the dam stops water and blocks sediment Types of fossil fuels o Coal is solid o Petroleum is liquid Formed in shallow basins within continents, lagoons, or continental shelves Mainly composed of fossil plankton and organic material Natural gas usually found on top of petroleum reservoirs. Petroleum because of plate tectonics Petroleum forms traps with folds and faults where petroleum and gas are captured and preserved until we get them out through wells. Definition of mineral resources o To have an economic value, a mineral resource must be concentrated and easily extractable o Ore is a naturally occurring material from which an economically valuable mineral can be extracted o Grade of an ore: concentration of material o Low grade is less valuable because of high concentration costs Geologic time scale and main milestones of life evolution o 4.6 billion years old o Oldest rock=3.9 billion years old o First abundant life= 570 million years o Largest mass extinction=250 million years o Extinction of dinosaurs=65 million o First humans= 2 million years o Precambrian- 85% of earth's history o Precambrian Internal heat production was 4-6 times higher than today Plate tectonics more active o Asphalt is a thick petroleum Rate of volcanism, subduction and plate production much higher than today o Phanerozoic- "visible life", started 570 million years ago, covers most of the evolution of life Paleozoic- era of trilobites Mesozoic- era of reptiles Cenozoic- right now, era of mammals Relative geologic time and laws of stratigraphy o Relative time tells me that A is younger/older than B o Principles: Uniformitarianism- physical processes we observe operating today also operated in the past but factors such as climate can change. Superposition- in sequence of sedimentary rocks, each layer must be younger than the one below, a layer of sediment cannot accumulate unless there's already a substrate on which it can collect. Layer at the bottom is the oldest Original horizontality- surfaces on which sediments accumulate are fairly horizontal, if they were steep they would likely slide downslope and not be preserved. Original continuity- sediments generally accumulate in continuous sheets. Cross-cutting relations- if one geological feature cuts across another, the feature that has been cut is older. Example, igneous dike cuts across a sequence of sedimentary beds, the beds must be older than the dike Inclusions- if an igneous intrusion contains fragments of another rock, the fragments must be older than the intrusion. If a layer of sediment deposited on an igneous layer includes pebbles of the igneous rock, then the sedimentary layer must be younger. Baked contacts- igneous intrusion metamorphoses surrounding rocks. The rock that has been baked must be older than the intrusion. Determining the age of a rock (absolute time) o Absolute time- tells me how old is A in years or millions of years, independently fro mother events o rocks or organisms. o Some minerals contain radioactive atoms that decay with time o The amount of these radioactive atoms is locked when the mineral is formed--becomes a solid. o The decay process is not affected by heat, pressure, chemical reactions and it occurs at a constant pace. o When minerals form from a magma (igneous) they incorporate some radioactive elements that start decaying when they become solid. o We call the radioactive element that is locked inside a mineral the parent isotope. o It decays to form a stable daughter isotope o Constant rate. o Decay rate (how fast a parent decays to form a daughter) is called half-life o The half-life can be a few seconds or many years o Decay of radioactive isotopes releases energy o Uranium/lead-good for rocks older than 10 mil years o Potassium/argon- good for rocks older than 100,000 years o Carbon-14 dating- good for only organic material younger than 70,000 years o To date a rock must know amount of parents, amount of daughter, half-life of parent. Characteristics and types of metamorphism o Agents Heat- makes rock more plastic Pressure- allows minerals to get squeezed, form bands Chemically active fluids- help form new minerals stable at this temp and pressure o Caused by solid state transformations of older rocks occurring deep in the crust o Minerals become oriented in bands or layers and can be stretched o New, mainly flat, minerals are formed o The size of the minerals becomes larger and larger as crystals grow up heat and pressure. o Solid-state process o Types Regional- during subduction and plate collision- pressure and heat Contact- near intruding magma- only heat o Regional- becomes banded, shows lineations, has equigranual texture, minerals are same size, layered texture given by sheeted and bladed minerals. o Chemical comp. of the bulk rock doesn't change but the minerals do- adapt to higher temps and pressure o Foilated- characterized by pressure, subduction zones--continentcontinent collisions o Texture of foliated- as metamorphism becomes more intense, bands go from very thin to thicker o Slate- weak metamorphism. Schist- more intense. Gneissstrongest. o Nonfoilated- form under normal burden pressure conditions or contact metamorphism--with heat from magma o These rocks don't have layers because they are formed by heat, not pressure. o Sandstone becomes Quartzite, limestone becomes marble. Common metamorphic and igneous rock names o Foilated- characterized by pressure, subduction zones--continentcontinent collisions o Texture of foliated- as metamorphism becomes more intense, bands go from very thin to thicker o Slate- weak metamorphism. Schist- more intense. Gneissstrongest. o Nonfoilated- form under normal burden pressure conditions or contact metamorphism--with heat from magma o These rocks don't have layers because they are formed by heat, not pressure. Mountain formation o Volcanic mountains- (Andes, Cascades) formed by oceanic crust subducting under continent or ocean and forming volcanic arms o Tectonic mountains (Himalayas, Alps) formed by deformation of the crust (all mountains except volcanoes) o Thickened continental crust and mountain belts- when two continents collide, neither is subducted and the two continents buckle and fold creating a thick crust. o Continental crust is less dense so it floats like an iceberg in the ocean o Isotasy- same way as the root of an iceberg gets closer to the surface as the exposed part melts, so the root of folded mountains belts is pushed up by the mantle as the mountain erodes. o Accretion- when plates collide, pieces of oceanic crust, microcontinents, island arcs can get caught between two continents-- can form mountains. o Accreted terranes- exotic fragments of continental and ocean crust brought to collide with continent from far-Alska, Rockies o Appalachains- formed through series of collisions during Paleozoic era when Africa collided with N. America o Orogeny- forms mountains. India collided with Asia 65 million years ago after the oceanic crust in between the two continents was subducted underneath Asia. o Tectonic mountains can be: Fault block mountains formed by crustal extention= Basin and Range of Nevada. Also folded mountains with crustal compression, convergent plate boundaries, folds, thrust faults, granite, regional metamorphism. basins Passive margins- formed by land-derived detrital sediments Active margins- close to plate boundaries, steep, narrow, tectonically unstable Subdivision of continental crust, composition, and age o Cratons- oldest part of crust, usually in the middle of the continent o Mountain belts- high elevations formed by continental collisions, or volcanic activity o Continental margins- coastal areas that connect to oceanic crust o Cratons- remains of very old continental collisions (made out of metamorphic rocks) and of mountains that are long gone and flattened out. They are the most stable parts- no earthquakes. Shields- exposed metamorphic rocks (Canadian shieldMinnesota) by Formed folding during continental collisions-Himalayas, Appalacians By accretion=Alaska o Continental margins- transition between continents and deep-sea Platform- part of craton covered by flat-lying sedimentary rocks deposited in shallow seas after the old mountain belt was flattended (Iowa metamorphic rocks of the shield are underneath limestone Different types of volcanic eruptions and what causes them o Effusive eruptions: produce mainly lava flows. Most yield lowviscosity basaltic lavas. Lava lakes develop around the vent, or lava sprays up in fountains that produce a cinder cone around the vent o Explosive eruptions: produce clouds and avalanches of pyroclastic debris. These eruptions happen when gas expands in the rising magma but cannot escape. Eventually the pressure becomes so great that it blasts the lava, along with volcanic rock, out of the volcano. Silicates o Granite, basalt, gabbro, peridotite o Independent tetrahedra: do not share oxygen atoms. Held together by attraction between tetrahedral and position ions. Includes olivines. o Single chains; tetrahedral link to form a chain by sharing two oxygen atoms. Most common type are pyroxenes. o Double chains: tetrahedral link to form a double chain by sharing two or three oxygen atoms. Amphiboles most common type. o Sheet silicates: tetrahedral share three oxygen atoms and link to form two-dimensional sheets. Micas, clay minerals. o Framework: each tetrahedron share all four oxygen atoms, forming 3D structure. Includes feldspar, quartz. Hot spots o Hawaii o When a mantle plume rises beneath oceanic lithosphere basaltic magma erupts at the surface of the sea floor and forms a submarine volcano. With time, the volcano grows up above sea surface and becomes an island. When the volcano emerges the basalt lava that erupts no longer freezes so quickly and thus flows as a thin sheet over a great distance. Thousands of thin basalt flows pile up, layer upon layer, to build a broad, dome-shaped shield volcano with gentle slopes. Shield volcanoes develop their shape because of the low-viscosity, hot basaltic lava that constitutes them. Zones of the Earth's interior (eg. Crust, mantle, lithosphere) o Crust Oceanic vs. continental Oceanic: 7-10 km thick Continental: 35-40 km thick Oxygen is the most abundant element in the crust Largest part of earth Upper mantle, transition zone, lower mantle Almost all of the mantle is solid rock Outer shell composed of rock, consists of the crust plus the uppermost part of the mantle Lies on top of the asthenosphere Location of earthquakes and plate boundaries o Three kinds of plate boundaries: Divergent- 2 plates move apart by sea-floor spreading. Marked by a mid-ocean ridge. Asthenospheric mantle rises beneath a mid-ocean ridge and partially melts forming magma. Magma rises to create oceanic crust. Lithosphere mantle thickens away from ridge axis as plate cools. o Mantle o Lithosphere Convergent- 2 plates move together, one plate subducts beneath the other--sinks into the mantel, only oceanic lithosphere can subduct. The boundary between the 2 plates is marked by a deep ocean trench. During subduction, melting above the downgoing plate produces amgma that rises to form a volcanic arc. Transform- one plate slides sideways past another, without the creation of a new plate or subduction of old one. boundary marked by large fault, fracture on which sliding occurs. Link segments of mid-ocean ridges. Mechanical and chemical weathering o Degrade rocks, fall apart o Agents: water, wind, air, organisms o Important: soils, valuable deposits (iron, alum, gold, clay) o Key role in carbon cycle--regulates earth's temp o Mechanical weathering: grinding down, small pieces of out big ones, no chemical change o Chemical weathering: chemical decomposition, falling apart into chemical components, ions in solution o Mechanical: water fill in cracks (frost wedging), mid-high latitudes, dry climates, salt crystallization, rocks that have been under pressure reach the surface, they expand and cause sheeting. Accelerated by plants, humans most effective o Chemical: mechanical prepares the ground for chemical, breaks down rocks to smaller particles, minerals directly dissolved, minerals like feldspars and quartz can break apart in hot, humid climates form clays and residual oxides. Metals can combine with oxygen to form oxides. Ie, rust. o Chemical=hot, humid o Mechanical=cold and hot and arid environments Desertification and the Sahel o Sahel is at the margins of the Sahara o Sahara is expanding in part for natural factors: fluctuating rainfall patterns with monsoons and droughts o Human contribution: destruction of forest and vegetation by grazing cattle, for firewood and because of overplanting (no crop rotation) o Formed by: Subtropical deserts (Sahara) are located in high pressure zones with descending air--no clouds, no rain Rain shadow and mid-latitude deserts are caused by topography (rising air loses moisture on western side of mountain and dry air descends the downwind side) Coastal deserts form close to cold ocean currents (Peru, SW Africa) Waves and wind in oceans o Waves are driven by wind and tides or earthquakes (tsunamis) o Energy from wind is transferred to the surface of the sea b/c of friction and is then moved by moving water o Stronger winds cause higher, choppier waves with high energy o Only the surface of the sea is affected by waves--wave motion decreases with depth and gets to almost zero at one-half a wavelength o Waves tend to erode headlands (steep cliffs) and deposit in bays (sand beaches)--the result in the end should be a flat coastline. Three types of plate boundaries Divergent- 2 plates move apart by sea-floor spreading. Marked by a mid-ocean ridge. Asthenospheric mantle rises beneath a mid-ocean ridge and partially melts forming magma. Magma rises to create oceanic crust. Lithosphere mantle thickens away from ridge axis as plate cools. Convergent- 2 plates move together, one plate subducts beneath the other--sinks into the mantel, only oceanic lithosphere can subduct. The boundary between the 2 plates is marked by a deep ocean trench. During subduction, melting above the downgoing plate produces amgma that rises to form a volcanic arc. Transform- one plate slides sideways past another, without the creation of a new plate or subduction of old one. boundary marked by large fault, fracture on which sliding occurs. Link segments of mid-ocean ridges. Factors controlling rock deformation o Stress- magnitude of force divided by the area o Compressive, tensile (stretching, extension) and shear stress o Strain- change in volume/shape of object resulting from stress o Plastic deformation Response produces folds-permanent deformation Anticline- older rocks in core Syncline-younger rocks in core Symmetrical/assymetrical Can get overturned or pushed to a horizontal position Domes and basins Produces permanent fractures Small cracks are joints-fractures with no evidence of movement Fractures with movement are faults Classified on basis of relative motion along fault plane Many fault planes are inclined so we call the two blocks separated by it hanging wall and footwall. Two main types of folds o Brittle deformation o Hinge: refers to the portion of the fold where curvature is greatest o Limbs: sides of the fold that show less curvature. o Domes: a fold with the shape of an overturned bowl o Basin: fold shaped like a right-side-up bowl. Three types of faults o Hanging wall block- the rock above the fault plane o Footwall block- rock below the fault plane o Normal- hanging wall goes down relative to footwall, due to crustal stretching o Oblique slip- hanging wall slips diagonally o Reverse- hanging wall goes up relative to footwall, due to crustal shortening, slope (dip) of fault is steep o Thrust- hanging wall goes up relative to footwall, due to crustal shortening, slope is not steep o Strike-slip- no vertical motion, one block slides sideways past the other, fault surface is nearly vertical o Vertical displacement- movement along the plane of the fault can be vertical, or horizontal One part goes up or down called normal or reverse Normal faults are result of extension Reverse faults are result of compression--also called thrust faults. o Horizontal displacement- strike-slip Transform faults San Andreas fault Factors affecting flooding o Artificial levees and dikes stop rivers from flooding o Channel of a river is bound by natural levees--ridges of coarser material deposited by river during floods o Flood plain is made of finer sediments in layers o Flat and fertile flood plains used for agriculture o Elimination of prairie and forests for farmlands and cities have caused increased surface runoff Types of igneous rocks and location on Earth's surface o Intrusive- cooled at depth, crystals visible--eg. Granite o Extrusive-cooled at surface, crystals not visible--eg. Basalt o Quartz, Plagioclase and Potassium feldspars, Biotite mica, Pyroxene, Amphibole, Olivine. o Formed by freezing of molten rock. o Form at mid-ocean ridges o Families: Light-colored minerals- quartz, feldspars Dark-colored minerals- biotite, pyroxene, amphibole, olivine ... View Full Document

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