Layers of Earth - 3 distinct layers

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1 Clicker Question What is the source of the energy that drives most earthquakes and volcanoes? A. Sunlight B. Radioactive decay inside the earth C. Meteorite impacts D. Ocean tides E. None of the above Web Exercise 1 Available - IL Compass 2g Web Site Today, Web Exercise 1 (Population Growth) available under Web Exercises button on IL Compass 2g Web site. It is submitted on-line + due by 1:00 pm Mon., 2/6. Instructions for completing Web Exercises are found on home page of Class Web site. 2-point penalty for every day assignment is late. No Web Ex. 1 is accepted after 2 pm on Friday., 2/10. Questions? Contact the TA For Students Who Recently Added GEOL 118 1) GEOL 118 Class Web Site: Summaries of Lecture notes, announcements, FAQ file, writing assignment. 2) Illinois Compass 2g: Student grades, Web Exercises, old exams #4 Earth Layers and Earth Materials () Layers of Earth - 3 distinct layers < Crust < Mantle < Core Crust - Outer Layer < Two kinds of crust: continental and oceanic. = Continental crust underlies continents. 4Average thickness ~35 km, ranges from km 4Silicic (granite) to intermediate in composition = Oceanic crust underlies ocean basins. 4Average thickness ~7 km 4Mafic (basalt) in composition 4Denser than continental crust Mantle - Middle Layer < Base of crust to 2,900 km < Mostly solid ultramafic rock (peridotite) < Denser than oceanic crust Fig. 1.15a 1

2 < Iron/nickel metal alloy (mostly iron) < 2,900 km depth to center of Earth (6,370 km) < Outer part = liquid, inner part = solid Core - Inner Layer Clicker Question Which part of the earth s interior is liquid? A. The crust B. The mantle C. The outer core D. The inner core E. None of the above Earth Materials - Diamond Why Study? < Rocks = aggregates of minerals < Importance to Society? < Importance to Geology? Quartz Granite with three minerals labeled Azurite Why Study? < are building blocks of the planet. = Understanding Earth requires understanding minerals, especially Earth s geologic history. < are used by society = Industrial minerals raw materials for manufacturing = Ore minerals sources of valuable metals = Gem minerals attract human passions Why Study? < are used by society Fig. 3.1a Fig. 3.1b Earth, 4th ed., Chapter 5 Another View 2

3 These are the largest mineral crystals known. Earth4, Fig. 5.9 < Naturally occurring - formed by nature Synthetic bismuth - Not a mineral Mineral - Rhodocrosite The crystals of gypsum grew by precipitation from the hot water that previously filled the cave. < Inorganic - not organic (C-based) chemical < Solid - not liquid or gas Mussel shell is composed of aragonite, a mineral. Living part of mussel (inside shell) is organic and not a mineral. Liquid water is not a mineral Ice is solid (mineral) < Definable chemical composition - can specify types and proportions of elements (mineral chemical formula) Quartz (SiO 2 ) Calcite (CaCO 3 ) < Crystal structure - Orderly arrangement of atoms < Glass has random atomic arrangement (amorphous) < Crystal structure controls shapes of crystal faces (flat shiny surfaces that form if mineral grows into open space) Crystal structure of halite (NaCl) also known as salt. Halite crystals 3

4 Clicker Question Which of the following does NOT apply to minerals? A. They are always crystalline. B. They have a defined chemical formula. C. They are never liquid. D. They are always transparent. E. They are naturally occurring Mineral Identification < Definitive way = determine chemical composition and crystal structure but NOT usually done that way < Usually distinct set of physical properties allows mineral identification = Hardness Physical Properties of = Specific Gravity - density = Cleavage = Reaction with acid = Many others Hardness < Resistance to scratching; soft mineral is easily scratched, hard mineral is difficult scratch < Talc is softest mineral, diamond is hardest < Quartz is relatively hard, calcite is relatively soft Quartz is harder than glass Quartz is harder than calcite Cleavage < Tendency of mineral to break along flat surfaces due to weak bonding. < Flat surfaces = cleavage faces (reflect how it breaks). < Can be challenging to identify cleavage vs. crystal faces. Hardness < Resistance to scratching; soft mineral is easily scratched, hard mineral is difficult scratch < Talc is softest mineral, diamond is hardest < Quartz is relatively hard, calcite is relatively soft Fig. 3.8g Quartz is harder than glass Calcite is softer than glass (and so quartz scratches calcite) 4

5 Reaction with Acid <Calcite fizzes, calcite dissolves releasing CO 2 gas CaCO 3 + H + à Ca 2+ + H 2 O + CO 2 (gas) Types of < are classified by chemical composition and crystal structure < Silicates - Most common in rocks and Earth (95% of Earth s crust); Contain silicon (Si) and oxygen (O) Fig. 3.7 f Silicate < Fundamental component of silicate minerals = silica tetrahedron (central Si atom surrounded by four O atoms in pyramid shape) = Below silica tetrahedron is portrayed in different ways: Silicate < Silicates are divided into several groups based on how silica tetrahedra link together and are arranged < Five major classes of silicates: isolated tetrahedra, single chain, double chain, sheet (2-d), framework (3-d) Fig. 3.9a Other Mineral Classes - Sulfides < Contain sulfide (S in reduced state), galena = PbS, pyrite "fool's gold" (FeS 2 ) Other Mineral Classes - Carbonates < Contain CO 3 (carbonate molecule), calcite = CaCO 3. Pyrite Calcite 5

6 Reaction with Acid <Calcite fizzes, calcite dissolves releasing CO 2 gas CaCO 3 + H + à Ca 2+ + H 2 O + CO 2 (gas) Fig. 3.7 f 6