Geo 1111 [A] Introduction to Earth Systems PDF

Geo 1111 [A]: Introduction to Earth Systems Lecture One Geology: Science of the planet earth -​ Examens earth as a system -​ Components: Atmosphere, Biosphere, Cryosphere, Lithosphere, Hydrosphere -​ Intellectual and practical activity encompassing the systemic stu...

Geo 1111 [A]: Introduction to Earth Systems Lecture One Geology: Science of the planet earth -​ Examens earth as a system -​ Components: Atmosphere, Biosphere, Cryosphere, Lithosphere, Hydrosphere -​ Intellectual and practical activity encompassing the systemic study of the structure and behaviour of the physical and natural world through observation Places Earth Scientists work: In the field or in the lab Different fields in geology: Engineering geology- Study of the aspects of geology relevant to understanding slope stability or to building tunnels, dams, mines, roads, or foundations Environmental geology- Study of the interactions between the environment and geologic materials and the contamination of the near surface realm of the Earth by pollutants Geochemistry- Study of the chemical composition and behaviour of Earth’s materials and chemical reactions in natural environments Geomorphology- Study of landscape formation and evolution Hydrogeology- Study of the movement of groundwater and it’s reaction w/ rock and soil Mineralogy- Study of physical properties, structure, and chemical behaviour of minerals Paleontology- Study of fossils and the record of life’s evolution in rocks Sedimentology- Study of sediments and their deposition Seismology- Study of earthquakes and Earth’s interior as revealed by earthquake waves Stratigraphy- Succession of sedimentary rock layers and how they display info on Earth’s history Structural geology- Study of rock deformation in response to the force that builds mountains Tectonics- Study of regional-scale geologic features Volcanology- Study of volcanoes Nature of the scientific inquiry: Science assumes the natural world in consistent and predictable -​ Goal: discover patterns in nature and use knowledge to make predictions -​ Collecting facts in important but understanding is very important *It’s not what you know, but HOW you know it* Hypothesis (model): Tentative (or untested) explanation -Should be: testable, powerful, and parasimonious(simple) Theory: Well tested and widely accepted view that the scientific community agrees best explains certain observable facts Law: Statement based on repeated experimental observations that describes some phenomenon of nature with a high degree of confidence -Does not explain why it happens Inductive method (Baconian): -Early stages - Data is collected w/o thinking about theory -Expect that an explanation will result from organizing and building large data sets Deductive method (Darwinian) -Later stages -focused - devised models used to account for observations and to make predictions about nature -repetitive Steps: 1)​ Data collection 2)​ Development of one or more working hypotheses 3)​ Development of observations and experiments to test the hypotheses 4)​ Acceptance, modification, or rejection *See slides for example* How is geology different from other sciences? 1)​ Large spatial scales and complex systems -​ Difficult or impossible to facilitate a controlled experiment -​ Observation and description acquire proportionately more importance 2)​ Immense time scales compared to human life -​ Cannot observe an entire process from start to finish (Only snapshots) -​ Spatial variation can be interpreted as temporal evolution Principle of uniformitarianism: Geological processes and natural laws that operate today have acted throughout geologic time Examples: -​ Oldest rock continent: 4.6 billion years old (age of Earth) -​ Extinction of dinosaurs: 65 million years ago -​ Evolution of Homo sapiens: 500 thousand years ago -​ Last glacial maximumL 15 000 years ag0 Duration of average earthquake: 10 degrees from the Earth’s poles -​ (N pole is moving 50 km/yr and weakening) -​ Magnetic field is composed of the North and South magnetic pole -​ Magnetic field allows use of compasses -​ Magnetic field occasionally ‘flips’ -​ Normal polarity (now) & Reverse polarity (Time of opposite poles) -Rock magnetism and paleomagnetism uses mineral magnetic alignment to detweming the direction and distance to magnetic poles - Steeper dip angles indicate rocks formed closer to the magnetic - Marine magnetic anomalies are bands of normal and reversed magnetic field signatures ​ - parallel magnetic bands preserved in rock under ocean  ​ - Symmetric “bar-code” anomaly pattern reflects plate motion away from ridge coupled magnetic field reversals Earth is layer by competing P and T forces cause complication -​ Increased depth= increased temperature= increased melting -​ Increased depth = increased pressure= increased rock strength Layers are defined by physical properties -​ Change depending on the temperature and depth  -​ Properties include: -​ Brittle solid -​ Deform plastically -​ Become liquid via melting -​ Main layers of the Earth’s interior are based on physical properties and hence mechanical strength Geothermal Gradient: Rate in which there is a gradual increase in the Earth’s temperature as depth increases -​ Varies considerably from place to place -​ Averages between about 10 degrees to 20 degrees celsius/km in the cruse -​ Note: Rate of increase in much less in the mantle and core Heat flow in the crust -​ Process called conduction -​ Reates of heat flow in the crust varies Mantle convection -​ No large change in temperature w/ depth in the mantle -​ Mantle must have an effective method of transmitting heat from the core outward Plate Tectonics -​ 1962 Harry Hess proposed seafloor spreading -​ Seafloor moves away from the mid-oceanic ridge due to mantle convection Convection: Circulation driven by rising hot material and/or sinking cooler material -​ 1965 J. Tuzo Wilson  -​ Earth is composed of lithospheric plates that move on asthenosphere due to convection in mantle -​ 7 major plates: several minor ones -​ When sufficiently cool & dense, the rocks may sink back into the mantle at subduction zones -​ OVerall young age for sea floor rocks (everywhere H2): ice or SiO2: quartz) Atoms- smallest particles of an element that retains all of the element’s chemical properties (distinguishing characteristic) Classifications of minerals Combination of elements to form minerals depends on a few characteristics of atoms of that element: 1)​ Relative abundance of available elements (w/in crust) O: 46%​ ​ Si: 28% Al: 10%​ ​ Fe: 6% Ca: 3000 km long Great Meteor Hotspot 150 Ma to today 2)​ Add Flux (H2O, CO2) -​ Addition of volatiles along plate margins reduced the melting temperature of a sold -​ Wet melting: Volatiles ‘disrupt’ chemical bonds of other compounds (specifically siO2) Location: Igneous activity along plate margins Subduction zones -​ Occur in conjunction w/ deep oceanic trenches (plate convergence margins) -​ Descending plate partially melts + release H2O (wet melting) -​ Rising magma can form either: -​ An island arc if in the ocean -​ A volcanic arc if on a continental margin -​ Associated w/ the Pacific Ocean basin -​ Region around the margin is known as the ‘Ring of Fire’ -​ Most of the world’s explosive volcanoes 3)​ Pressure decrease -​ Hi-P results in higher T to melt solid (Bonds are closer together=stronger) -​ If quickly release Hi-P (at same T), solid will melt -​ Crustal decompression (plate divergent margins) Location: Igneous activity along plate margin Spreading centers  -​ Greatest volume of volcanic rock is produced along the oceanic ridge system (plate divergence) -​ Mechanism of (decompression) melting -​ Lithosphere pulls apart -​ Less pressure on underlying rocks -​ Results in partial melting of mantle -​ Large quantities of basaltic magma produced -​ Polarizing microscopes and thin sections show the different compositions Magma compositions: 1) Ultramafic Igneous rocks.. Silicates dominate Dark (ferromagnesian) silicates -​ Olivine -​ Pyroxene -​ Amphibole -​ Biotite mica -2,6 Ga 2) Mafic Dark (ferromagnesian) silicates -​ Olivine -​ Pyroxene -​ Amphibole -​ Biotite mica -45-55 wt% siO2 -+ MgO, FeO, CaO -Fluid, low volatile concentration Where does rock come from: Volcanic  -​ Erupt, flow, or explode at the Earth’s surface -​ Cooling times range from seconds to years -​ May have no crystal (all glass) or small + large crystals -​ Basalt is the archtype- compose of very fine grainded minerals (chiefly Fe- and Mg-rich minerals, ~50% siO2), forms mostly on the ocean flloor; 70% of all magma erupted 3) Intermediate (andestic) composition Igneous rocks… Silicates dominate -​ Contains 55-55-65 wt% SiO2 -​ Relative to granitic: more FeO & MgO, less Na2O & K2O -​ Less volatile, less viscous -​ Associated w/ explosive volcanic activity 4)​ Felsic Igneous rocks… Silicates dominate -Light (nonferromagnesian) silicates - quartz -muscovite mica -feldspars ->65 wt% SiO2 - + K2O, Al2O3, Na2O -Viscous Where does rock come from: Plutonic -​ Intrude at depths of 0.1’s-10’s of km within the crust -​ Mm-cm scale crystals are generally evident -​ Can form huge masses that likely cool over a million years -​ Granite is the archetype- composed of K-, Na-, Si-rich (~70% siO2) minerals and commonly found on the continents Igneous Texture Texture: Describes the overall appearance of a rock based on the size, shape, and arrangement of interlocking mineral -​ Factors affecting crystal size  1)​ Rate of cooling -​ Slow rate promotes the growth of fewer but larger crystals -​ Fast rate forms many small crystals -​ Very fast rate forms glass 2)​ Amount of silica (siO2) 3)​ Amount of dissolved gases Igneous rock textures… Phaneritic (coarse-grained) -​ Crystals can be seen without a microscope -​ Why?? Aphanitic (fine-grained) -​ Microscopic crystals -​ Why?? -​ May contain vesicles (holes from gas bubbles) Porphyritic -​ Large + small crystal -​ Large crystals, called phenocrysts, are embedded in a matrix od smaller crystals, called the groundmass -​ Why??  Glassy -​ No crystals visible -​ Pumice: felsic rock full of vesicles; its floats -​ Obsidian: Glassy felsic rock, no vesicles -​ Why (glass, foamy)?? Pyroclastic -​ Fragments ejected during a violent volcanic eruption -​ Often appear to be layered or composed of shattered rocks Pegmatitic -Exceptionally coarse grained - Form in the late stages of crystallization of granitic magmas w/ high volatile content Lecture Four : Earth Materials II & III