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UO GEOL 102 - Exam 1 Study Guide
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GEOL 102 1st EditionExam # 1 Study Guide Lectures: 1 - 5Lecture 1 (Thursday 1/8)Alfred Wegener introduced the idea of continental drift based on the evidence of: fit of continental coastlines, glacial deposits, geologic evidence of climatic zones, and fossil evidence (distribution along now-far coasts)The compositional Earth consists of the crust, mantle, and core.The continental crust density is 2.6 gm/cm cubed, 30-40 km thick; the oceanic crust density is 3 gm/cm cubed, 25-10 km thickThe mantle density is 3 gm/cm cubedOuter core is very dense and the inner core is even denserThe rheology (material behavior) of the lithosphere is brittle and prone to breaking under stress, while the asthenosphere flowsThe seafloor has fractures along mid-ocean ridges; scattered with oceanic islands, seamounts, guyots, and trenches; has a high heat flow at mid-ocean ridges; there was a breakthrough ofsea-floor understanding with the discovery of magnetic anomaliesMagnetic anomaly properties: molten rock cools and preserves properties of its prevailing field; strength, orientation, and polarity of Earth’s magnetic field varies with timeThe theory of plate tectonics emerged in the 1960s and stated that plates move relative to one another and that geologic activity is focused at plate boundariesDivergent plate boundaries: plates move away from one another (mid-ocean ridges); asthenosphere upwells, forms magma, and creates new crust; the lithosphere cools and thickens away from the ridge axisConvergent plate boundaries: plates move towards each other; the boundary where crust is consumed; occurs with oceanic-continental plates and continental-continental plates; is the boundary where partial melting arc volcanism, accretionary prisms, and earthquakes occurTransform plate boundaries: plates slide along each other; crust is neither created nor consumedLecture 2 (Tuesday 1/13)Over 100 volcanoes on Earth do not occur along plate boundaries, but are hot, rising plumes of magma, plate motion carries these volcanoes away from the fixed plumes (such was the formation of Hawaii, the Aleutians, the Philippines) Principles of relative dating help to determine the geologic time a rock has been in existence, and include uniformitarianism, superposition, original horizontality, original continuity, and cross-cutting relationshipsUniformitarianism: processes in action today were also acting in the past, indicates a slowness of geologic processesSuperposition: rock layers towards the bottom are the oldest, and rock layers at the top are younger, as they were deposited laterOriginal horizontality: rock layers were likely laid down horizontal and parallel to the Earth Original continuity: rock beds are laid down the same across space (think of Grand Canyon, OR’s Painted Hills)Cross-cutting relationships: that which cuts through rock layers is younger than the rock layers it cutsUnconformities are gaps in the geologic time record and include angular unconformities, nonconformities, and disconformitiesAngular unconformities: rock layers are tilted or folded before the surface is eroded and further deposition occursNonconformities: sedimentary rock layer(s) overlie igneous or metamorphic rock layersDisconformities: parallel sedimentary rock layers separate an erosion surface (this looks continuous bed could easily have (a) missing/eroded layer(s))Lecture 3 (Thursday 1/15)Absolute dating is another way of measuring geologic time and includes radiometric techniques,isotopic evidence, magnetostratigraphy (normal and reversed polarity timelines),dendrochronology (tree rings), fission tracks, cosmogenic radionuclides (isotopes from cosmic rays), and rhythmic dating (annual layers of sediments are counted)Naturally occurring isotopes are elements with different atomic weight (protons and neutrons). Because their weight is different from a standard isotope, they are unstable and will decay and break down. They account for a tiny fraction of mass in rocks or organic material.Radioactive decay: Parent isotopes decay into daughter isotopes, decay begins when rock cools to lower than its blocking temperature (isotopes can no longer escape the crystal lattice at this temperature)The half-life is the time needed for half of a group’s isotopes to decay. The key for determining the age in the way is to look at the ratio of parent isotopes to daughter isotopes and comparing this with the half-lifeThe age of the Earth has been calculated in multiple ways:Hutton: measured time through sedimentation calculation, proves Earth is at least 20 millionyears oldLord Kelvin: measured time through cooling calculations, proves Earth is at least 20 million years oldSalt accumulation in Earth proves Earth is at least 90 million years oldOldest rocks on Earth (in Australia) are zircon crystals in sedimentary rock, proves Earth is at least 4.3 billion years oldMoon rocks: 4.4-4.5 billion years old, formed originally as one with Earth, moon rocks are preserved since they are not consumed by plate tectonic activityLandscape evolution: at about 30 km thick, the crust is considered to be continental, not oceanic. Continental crust “floats” on denser mantle rocks based on the principle of isostaticuplift (removing mass by surface erosion makes the crust more buoyant, and the mantle pushes it up more). Crustal thickness is required to maintain mountainous topographyDrainage density is the length of channels divided by the drainage amountRelief is the difference between elevation of ridges and the elevation of valleysSlope is how steep an incline is (rise over run)Lecture 4 (Tuesday 1/20)Landscape Evolution theorists Grove Karl Gilbert and William Morris Davis developed the main theories of landscape evolutionGrove Karl Gilbert: interactions between process and form, hilltops tend to be concave and river profiles tend to be concave, landscapes tend to erode at a ‘steady’ rateWilliam Morris Davis: developed the geographical cycle: a highly influential paradigm, mountains are uplifted and then decline through time, separated landscape evolution into four main stagesStage 1: high mean elevation, low relief; Stage 2: high elevation and high relief as valleys catch up; Stage 3: valleys widen laterally and hill slopes degrade; Stage 4: landscape has become a featureless plain (peneplain)Water and the Hydrologic Cycle: 70% of the Earth’s surface is covered with water, the hydrosphere includes 1.36 billion cubic kilometers and the ocean bottom


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