GEOL 105 Test 1 Notes
GEOL 105 Test 1 Notes Geology 105
University of Louisiana at Lafayette
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Date Created: 09/20/16
UNDERSTANDING EARTH • Earth is dynamic constantly changing Characterized by constant change, activity, etc. • Earth subsystems Atmosphere Biosphere Hydrosphere ‣ has to do with earth's water ‣ Majority is salt water Lithosphere Mantle Core • What is geology? comes from Greek words "geo" (earth) and "logos" (study) The study of earth • Divisions Physical geology Historical geology • Geology and the Formulation of Theories scientific theory- explanation of some aspect of the natural world acquired through the scientific method and repeatedly confirmed through observation and experimentation ‣ plate tectonics theory ‣ The rock cycle ‣ Organic evolution ‣ Geologic time and uniformitarianism • Scientific Method (steps) accumulate observations Make one or more hypothesis Test the hypothesis by experiment of additional observations If one hypothesis is confirmed as the probable explanation it is called a scientific theory • Why study earth? understanding our surroundings ‣ "if it can't be grown, it has to be mined" Predicting, controlling, avoiding geological hazards Advancement of civilization ‣ economics, politics Protect our environment • How does Geology affect our everyday lives? natural events Economics and politics Our role as decision makers Consumers and citizens Sustainable development • Global Geological and environmental issues facing mankind overpopulation ‣ 2014 - 7.1billion ‣ 2045 ~ 9 billion Global warming Temperature change Increase in sea level Significance of shorelines • Origin of the universe and solar system, and earth's place in them BIG questions ‣ what's the origin of the universe? ‣ What has been its history? ‣ What is its eventual fate or will it go on forever? ‣ How common are planets around other stars? ‣ Is there life elsewhere? ‣ Is life rare, usual, or even unique? • origin of the universe the Big Bang model ‣ 14 billion years ago ‣ hot, dense state, expansion, cooling and a less dense state ‣ Evidence: • expanding universe • Background radiation = faint afterglow ‣ Universe continued expanding and cooling ‣ Stars and galaxies formed, and chemical makeup was changed by matter given off as stars die • Origin of the solar system Solar Nebula Theory (4.6BYA) ‣ condensation and collapse of gas and dust in an arm of the Milky Way Galaxy ‣ Cloud of material formed a counter-clockwise rotation disk ‣ Material concentrated in center - formed the Sun and surrounding solar nebula ‣ Rotation within the solar nebula formed localized eddies where material concentrated into planetesimals that eventually formed into planets • Why is Earth a dynamic planet? The core ‣ solid inner ‣ Liquid outer ‣ 16%of earth's volume The mantle ‣ surrounds the core ‣ About 83% of earth's volume ‣ 3 distinct zones • Lower mantle ‣ Asthenosphere • surrounds lower mantle • Behaves plastically - flows slowly • Surrounded by solid, upper mantle ‣ Upper mantle Lithosphere = solid upper mantle + crust ‣ broken into plates ‣ Plates float on asthenosphere The crust ‣ Oceanic (thinner) ‣ Continental (thicker) • Plate Tectonic Theory movement of the plates is caused by convection in the mantle ‣ Divergent: move apart • Mid-Atlantic ridge ‣ Convergent: move together • volcanoes and earthquakes • Mountain ranges ‣ Transform: move along Where does the heat come from? ‣ Radioactive decay (e.g., uranium) ‣ Earth loses 5 million kW every hour (or 44.2 trillion kW per year) - enough to keep 50 million lightbulbs burning for an hour • The Rock Cycle a rock is an aggregate of minerals There are 3 main types of rock: ‣ Igneous • form from melted rock material (lava or magma) ‣ Sedimentary • pieces of other rocks (sediments) ‣ Metamorphic • have been exposed to heat/pressure Any rock type can come from any rock type • Organic Evolution All present day organisms have descended from earlier forms ‣ suggests that all present day organisms are related to organisms in the past ‣ Natural selection results in the survival of those best suited to their environment ("survival of the fittest") Fossils ‣ document changes in life forms over time • Geologic Time Earth is about 4.6 billion years old Oldest rocks are about 4 billion years old Oldest fossils are about 3.7 years old Changes took place over long periods of time Geologic Time • Millions and billions of years • Time is measured Relative Absolute (years) Relative ‣ Bottom layer: older ‣ Top layer: younger Absolute ‣ Henri Becquerel discovered radioactivity in 1896 ‣ Ernest Rutherford discovered half-life and age dating of rocks • Absolute Age Dating Radiometric dating ‣ Uses the fact that some elements (like Uranium) are not stable and they decay over time ‣ Decay is constant • Geological Time Scale Originally based on relative age dates and fossil evidence Numerical dates from Radiometric dating Divisions are different lengths Eon, Era, Period, Epoch • Principle of Uniformitarianism • Why Study Geology? Natural resources ‣ if it can't be grown, it has to be mined Protect our environment Predict, control, and avoid geological hazards Understand our surroundings ‣ We're part of it! • Plate tectonics Dominant process affecting the evolution of our planet Lithosphere = rigid plates Plates are created and destroyed at plate boundaries The center of plates tend to be stable • Early Ideas - Plate Tectonics Continental Fit ‣ 1620 - Sir Francis Bacon • Noticed the continents fit together like a puzzle The crust was locating on a fluid interior ‣ 1782 - Benjamin Franklin Edward Suess (1885) Fossil evidence - Glossopteris ‣ India, Australia, South Africa, South America Supercontinent Gondwana = all southern continents ‣ Gondwana: province in India with Glosspteris Suess thought continents were connected by land bridges Frank Taylor (1910) ‣ Continental drift theory ‣ Mountains originate as result of lateral movement of continents ‣ Larger continent broke apart and formed present-day continents ‣ Mechanism: gigantic tidal forces Continental Drift (1915) ‣ Alfred Wegener (1880-1930): Origin of Continents • History of Plate Tectonics Continental drift: Pangea • The Evidence Continental Fit ‣ Not perfect because of erosion and deposition ‣ Bullard (1965): best fit at depth of 2000m Rocks Mountain Ranges Climate ‣ Coal in Artic and Antartic ‣ Glacial Evidence • Striations Rock fragments scrape and polish bedrock: Striations (scratches) Direction of ice movement • Glacial till If continents did not move in the past: ‣ Ice moved from the oceans onto land- unlikely ‣ Ice formed in tropical to subtropical climate- impossible Fossils ‣ Glossopteris flora and other land plants ‣ Seeds too large to be transported across oceans ‣ Today's climate of South America, Africa, India, Antartica, and Australia much too diverse to support the Glossopteris flora Mesosaurus ‣ Freshwater reptile - couldn't have survived in oceans ‣ Found ONLY in Brazil and South Africa ‣ If it could swim the oceans, it would be widely found and not just in those two locations Evidence for Pangea ‣ Continental Fit ‣ Related rocks and mountains ‣ Climate ‣ Animal Habitats ‣ ....but, Wegener had no MECHANISM to move the continents. ‣ Hypothesis rejected.. • Continental Drift Despite overwhelming evidence not accepted until... New evidence from ‣ Magnetic field (1950's) ‣ Ocean basins • Topography by sonar • Ocean drilling • Earth's magnetic field Magnetism - results from the spin of electrons in some solids (especially iron) and moving electricity Earth is dipolar- strength and location of the poles vary Field lines coverage where magnetic force is strongest (poles) ‣ Lines spread out where it is weak (equator) • Paleomagnetism Magnetite, Fe3O4 (found in volcanic rocks) Orientation and strength Measure magnetization of rock and determine at which latitude was formed or where the pole was at the time Paleomagnetism: the study of the magnetic orientation of ancient rocks Curie Point (@700degrees C or 1400degrees F) Paleomagnetism in the 1950s - proof of polar wandering? • Magnetic Reversals Magnetic field weakens, temporarily disappears, and returns with poles reversed ‣ Every 200,000-300,000 years or so ‣ Longer since the last one - more than 700,000 years ago • Mid-Ocean Ridge System • Sea floor Spreading 1962 - Harry Hess; oceans rifting apart at the mid-ocean ridges, new sea floor forms, and continents move apart Mantle convection proposed as driving mechanism • Confirmation of Seafloor Spreading Deep Sea Drilling Interpretation of magnetism stripe pattern confirmed by ocean drilling Oceans are geologically young, younger than 180 million years (oldest continental crust: 4+ billion years) Sediments are hundreds of meters thick near continents and absent at oceanic ridges Fossil evidence/age dating = more proof of the age of oceanic crust • Plate Tectonic Theory Lithosphere is divided into plates - edges are ridges, trenches, and transform faults Lithosphere overlies a much weaker and hotter (plastic) asthenosphere Oceanic crust thinner and more dense Continental crust is thicker and less dense • Supercontinent Cycle All the land assets come together to form a supercontinent Break apart Come together again about every 500 million years • Basic Plate Boundaries Three types ‣ Divergent • The Wilson Cycle Rifting Formation of a linear sea Full ocean basin Subduction begins Closing of an ocean basin Collision of continents = orogeny Erosion ‣ Convergent • Plates move towards each other • Deformation, volcanism, earthquakes, metamorphism, economic minerals • 3 types, depending on crust Oceanic-Oceanic Oceanic-Continental Continental-Continental ‣ Transform • San Andreas, California • Transform fault • Hot Spots and Mantle Plumes Intraplate- within a tectonic plate Stationary hot spot under the plate "Records" plate motion • Tectonic Plate Movement How do we find the speed with which the plates are moving? ‣ Age of sediments ‣ Magnetic anomalies ‣ Direct measurement with Satellite Laser Ranging techniques (SLR) ‣ Hot spots • The driving force Heat • Convection cells • Hot stuff rises • Cold stuff sinks • Other mechanics for plate movement Ridge push - slab pull • Plate Tectonics and Natural Resources Gold, copper, lead, silver, tin, and zinc associated with igneous and hydrothermal processes • Plate Tectonics and Life Climate and geographic Boundaries Biotic provinces- areas with distinct assemblages of plants and animals MINERALS • What are minerals? Solids Inorganic Naturally occurring Crystalline = arranged atoms Specific chemical composition Characteristic physical properties • Why study minerals? Used in: fertilizers, glass, computers, cell phones, paint, make-up, industrial uses, jewelry, etc. • Minerals Economically important Valuable as gemstones • What is a rock? An aggregation of one or more minerals We will discuss rocks starting Chapter 4 and in later chapters • Building Blocks of minerals Atoms ‣ Structures of atoms • Electrons: energy/ electron she'll • Limited number allowed in one shell (2,8) • Completely filled outer shell is stable (ex: noble gasses) Elements Isotopes ‣ Variations of elements ‣ Different atomic mass numbers (P+N) ‣ Most are stable ‣ Some are unstable = radioactive • Atoms and Elements Matter: anything that has mass and takes up space Elements: cannot be split into substances of different composition Atoms: smallest particle of an element that still retains the properties of the element ‣ Protons ‣ Neutrons ‣ Electrons Atomic Number: determined by the number of protons • Bonding and Compounds Compounds: formed by the bonding of atoms of two or more elements - interaction between electrons Two important types of bonds in mineral formation ‣ Ionic • Transfer of electrons ‣ Covalent • Sharing electrons Other types ‣ Metallic bonding: atoms move freely from one atom to another; occurs in metals; accounts for metallic luster, electrical & thermal conductivity, and malleability ‣ Van der Waals bonding: weak attractive once between atoms that have no electrons available for bonding • Graphite- covenant bonds and Van der Waals bonds • Mineraloid Same, but different: no systematic internal arrangement of atoms! Amorphous ‣ Example: Opal • Minerals, cont.. Chemical composition ‣ Shown by a chemical formula such as NaCl (Halite) More than 3,800 (always growing) identified ‣ Less than 25 are common as rock forming minerals ‣ They are composed of the most abundant elements found in the crust *Top 8 elements of the periodic table make up 98.5% of the Earth's crust* Silica Tetrahedra • Mineral Groups Silicates ‣ Combo between silica tetrahedra and other ions • Mineral Identification Physical properties of minerals ‣ All minerals have characteristic properties ‣ Determined by the internal structure and chemical composition ‣ Most properties are constant, but some variation exists, especially in color Color ‣ Impurities ‣ Chemical formula Luster (quality of reflected light) ‣ Metallic ‣ Non-metallic • Glassy • Earthy • Silky • Pearly • Waxy • Dull Crystal Form ‣ Can occur in a variety of shapes which reflect the orderly internal arrangement o atoms ‣ Reflects internal geometry and composition ‣ Perfect crystals are rare, but may be useful in identification Cleavage or Fracture ‣ Cleavage- minerals that break or split alone smooth planes of weakness determined by the strength of their chemical bonds • Quality: perfect, good, poor • Direction • Angles of intersection ‣ Fracture- mineral breakage alone irregular surfaces • Uneven • Conchoidal Hardness ‣ Internal structure and strength of bonds ‣ Based on the Mohs scale from 1 to 10 • Quartz has a harness of 7 and shows conchoidal fracture Streak ‣ The color of the powder form of the mineral can help you identify it Specific Gravity (Density) Smell Taste (Halite) Striations (Plagioclase feldspar) Magnetic (Magnetite) Double refraction (Calcite) Chemical Tests- reaction to HCl • How do we really do it??? Chemical sets X-Ray diffraction Thin sections • How do minerals form? From molten rock material Hot water- hydrothermal From water- evaporation, animals Chemical weathering- clays Metamorphism • How important are minerals? Natural resources ‣ Matallic- copper, tin, iron, ore, etc. ‣ Non-metallic- sand and gravel, stone, salt, etc. ‣ Energy- petroleum, natural gas, coal, uranium, etc. Not all resources are reserves ‣ Accessibility ‣ Cost vs. value
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