Geology 101, Week 3 Lecture Notes
Geology 101, Week 3 Lecture Notes GEO 101
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This 17 page Class Notes was uploaded by Jamie Bynum on Thursday September 1, 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 7 views. For similar materials see Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 09/01/16
Lecture: “Plate Tectonics” August 30, 2016 Professor: Dr. Keene - The current view of the Earth is only a small portion of it’s histo- ry; only a tiny part of Earth’s history looked the way it does to- day - The outer crust of the Earth is ALWAYS moving; if it were to stop moving, our planet would become a dead planet - A tectonic plate is a piece of lithosphere; not just crust - The Earth has many small and many large plates; some plates are 100% oceanic, while some are part oceanic, part continen- tal - The movement of plates takes place at a very slow pace; plates move 1 to 15 cm per year • Continental Margins: Active: Plate interactions (earthquakes, volcanoes, etc.) - - Passive: No plate boundaries (quiet) The plate tectonic theory was created by Alfred Wegner Six Major Pieces of Evidence for Plate Tectonics 1. Shape of continents—they ﬁt together 2. Paleozoic glacier deposits—extent; direction of movement Ancient climate belts—glaciated, desert, tropics 3. 4. Distribution of fossils—plants and animals could travel due to Pangaea 5. Distribution of ancient rocks—speciﬁc chemical composition 6. Paleomagnetism—magnetization of rocks throughout history Paleomagnetism: *Different rock layers have different magnetic ﬁelds (different magnetic North) *Must take into account the fact that the continents are moving Plate tectonic proof helps us reconstruct plate movement What Makes Plates Move? 1. Mid-ocean ridge (mountain range of volcanoes 2. Sediment changes thickness (thickens with age) 3. Seamount chain (extinct volcanoes with an active vol- cano) 4. Trench (where plates enter the asthenosphere) 5. Fracture zones (mid-ocean ridges; not continuous) 6. Earthquake distribution (focused on plate boundaries) 7. Magnetic reversal (Earth’s magnetic ﬁeld reverses) - As rock is created at ridges, it takes on Earth’s magnetic polari- ty Sea-Floor Spreading and Continental Drift - New sea ﬂoor is created at a mid-ocean ridge - Lithosphere plate moves with the continent - Sea-ﬂoor spreading is the cause of continental drift (pushes the continents) ***Plates get recycled in trenches*** How do we know where plate boundaries are? Earthquakes 3 Major Types of Boundaries 1. Divergent 2. Convergent 3. Transform Divergent Boundaries - Two plates move apart *Mid-ocean Ridges *Continental Drift Mid-Ocean Ridges - What makes them move? Heat of the asthenosphere causes them to rise - Cooling creates topography - Gravity acts on it Continental Drift - Divergent boundary in continent - Mid-ocean ridge beneath continent - Eventually continent will crack apart; ocean forms between the two pieces Convergent Boundaries - Two plates move toward each other *Subduction *Collision Subduction - Reason for earthquakes at plate boundaries - Trenches One plate sinks - - Continental crust NEVER gets subducted (too buoyant) - Oldest oceanic crust sinks (due to density) Subduction: Oceanic/Continental - Oceanic crust sinks - Water acts as volatile (such as gasoline on a ﬁre); lowers the melting temperature therefore causing lots of melting in the as- thenosphere; creates heat that rises -Always near a line of volcanoes Subduction: Oceanic/Oceanic - Whichever crust is older will sink (older crust = more dense) - Water acts as volatile; lowers melting temperature therefore causing lots of melting in the asthenosphere; creates heat that rises - Always near a volcanic island arc Collision: Continent/Continent - Plates come at one another and hit head on - The plates crash and crumble up, such as two cars hitting head on; this causes the crust to grow higher into mountains Transform Boundaries (Fault Boundaries) Two plates sliding past one another - - Mostly oceanic/oceanic, but can sometimes be continental/con- tinental - Majorly causes earthquakes Fracture zones (when active) = transform boundaries *Triple junctions are the places where three plates intersect *Hot spots are deﬁned by volcanoes that are not on a plate boundary; hot spots never move, the plates move over them What makes plates move? Ridge push (gravity) Slab pull (oceanic crust sinking) Lecture: Minerals September 1, 2016 Professor: Dr. Keene • Element: Simplest chemical substance *Cannot be broken down into other substances *All matter is made of elements Atom: Smallest unit of an element • *Composed of: Protons (Positive Charge) Neutrons (Neutral Charge) Electrons (Negative Charge) Other subatomic particles - You can ﬁnd out what an element is by counting its protons (atomic number) - The number of electrons determines the element’s charge (ion) - Neutrons + protons = isotope (atomic weight) *The type of isotope an element is will change its actions - Two kinds of isotopes: *Stable *Unstable (Radioactive; may spontaneously burst) How do atoms join? - Chemical bonds—attractive force that holds two or more atoms together Types of chemical bonds 1. Covalent Bonds: Atoms share electrons *sharing electrons make it more stable and strong 2. Ionic Bonds: Transfers of electron *one atom is more positive, while the other is more negative 3. Metallic Bond: Sharing a sea of electrons *easily shaped *good conductor 4. Van der Waals Force: Weak charge in a neutral atom or molecule *holds molecules together, such as water molecules -When atoms are bonded together, they make a molecule Five Major Characteristics of Minerals 1. Naturally occurring 2. Solid 3. Inorganic 4. Deﬁnable chemical composition 5. Speciﬁc crystalline structure - A chemical formula is basically a recipe: element + amount of that element - A crystalline structure is when atoms are in a ﬁxed pattern Identifying Minerals - Can’t use the composition alone; must use crystalline structure as well Minerals Form in Five Ways: 1. Solidiﬁcation of a melt (most common) *Freezing *Many minerals created out of one melt 2. Precipitation from a solution *Atoms or molecules in liquid come out of solution 3.Solid state diffusion *Atoms moving in a NON-MELTED SOLID *Caused by pressure and heat *A new mineral forms from an old one 4. Biomineralization *Occurs when an organism creates precipitation from a solution 5.Fumarolic Mineralization *Crystallization from a vapor (like in geysers and volcanoes) 8 Methods to Identifying Minerals 1. Color *Can vary due to impurities *Least accurate method 2. Streak *Color in powdered form (often different from visible color) *Powdering reduces the impurity that causes it to be a different color 3. Luster *Way minerals scatter light *Two main classiﬁcations are metallic and non-metallic 4. Hardness *Determines the strength of chemical bonds 5. Speciﬁc Gravity *Measures density 6. Crystal Form (Habit) *The shape of a mineral if left to grow without any restrictions *NOT THE SAME AS CRYSTAL STRUCTURE* 7. Fracture and Cleavage *Cleavage is tendency to break along weak bonding planes (identiﬁed by a ﬂat, shiny surface) *Fracture—Planes equal strength *The difference between cleavage and a crystal face is that cleavage has a repeating pattern, while a crystal face does not 8. Special Properties *Magnetism *Reaction to hydrochloric acid *Taste *Smell Mineral Groups -Minerals are grouped according to their chemical similarities -Silicates are the most common mineral group Silicates - Base structure of all silicates is the tetrahedron - The ratio of O to Si determines the group - Tetrahedron are linked in various patterns Two main silicate groups 1. Maﬁc * Heavier Elements * Dark Colored * More Dense 2. Felsic * Lighter Elements * Light Colored * Less Dense ****Minerals are important because we use them EVERY DAY**** Rocks - Rocks are made of minerals Three Major Groups 1. Igneous—Forms from magma or lava 2. Sedimentary—Forms from sediment 3. Metamorphic—Forms from being changed by heat or pressure
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