Geology Midterm Practice PDF

Unit One - Physical Geology The study of Earth’s materials and the processes that shape and modify the planet. In order to study the Earth, we use the scientific method. 1. Make observations 2. Develop a hypothesis 3. Test the hypothesis 4. Develop a theory When a hypothesis is elevated to a theor...

Unit One - Physical Geology The study of Earth’s materials and the processes that shape and modify the planet. In order to study the Earth, we use the scientific method. 1. Make observations 2. Develop a hypothesis 3. Test the hypothesis 4. Develop a theory When a hypothesis is elevated to a theory which is observed throughout the universe, we call that a law. The Big Bang! The universe that we see expands from a central point. As matter accumulates, stars begin to form. The first generation stars are larger and burn hotter than later generation stars. Stars have a life cycle. The stellar nucleosynthesis theory tells us that heavier elements are formed by fusion reactions during a star’s life cycle. What does our solar system look like? The inner, terrestrial planets are smaller, rocky bodies. The outer, Jovian planets are gas giants. The asteroid belt formed due to Jupiter’s gravity. Earth’s Structure Earth has an inner core (solid), outer core (liquid), mantle, and crust structure. How do we know? Seismic waves. The magnetic field is created due to the friction between that liquid outer core and the spinning, solid inner core. The asthenosphere is the upper mantle material that behaves with a soft, plastic behavior. Earth’s atmosphere was created because the magnetic field allowed for solar wind to be deflected, which allowed gasses emitted from volcanic eruptions to get trapped due to gravity. All internal processes within the Earth are driven by the heat from Earth’s formation and radioactive decay. Unit Two - Plate Tectonics Plate Tectonics Theory Continental Drift Theory proposed by Alfred Wegener. Evidence: Fit of the continents. Fossil Evidence: Fossils that match across separated continents. Geologic units that match across separated continents. This theory was universally panned. Why? We needed to understand seafloor spreading in order to develop the Plate Tectonics Theory. Wegener didn’t have a mechanism for plate movement. How and Why do plates Move? Mantle Convection (caused by density) Ridge push Slab Pull Crust isn’t the same age. Continental Crust, the oldest is 3.8 billion years old Oceanic crust, the oldest is 180 million years old Divergent Boundaries Created by extensional stress Forms mid-ocean ridges and rift valleys. Convergent Boundaries Created by compressional stress. Continental collision Subduction zones - accretionary prisms form here; extrusive igneous rocks form at volcanic arcs, island arcs, and hot spots. Ocean-Continent: Oceanic plate subducts due to density Examples: Cascades, Andes, Mt. Etna, Mt. Vesuvius Ocean-Ocean: The older oceanic plate subducts because it is cooler and denser. Ocean-ocean creates island arcs and back arc basins. Example: Mt. Ontake - island arc at ocean-ocean boundary Transform Boundaries Caused by shear stress Slide against one another Examples: San Andreas Fault, California Hot Spots How do they work? A stationary plume is in the mantle. As lithosphere moves over it, new crust is created Older crust that is no longer volcanically active is pushed away from the plume in the direction of plate movement. Unit 3 - Minerals What is a mineral? Naturally occurring Solid Crystalline structure Definite chemical composition A mineral can have the same chemical composition as another. How do we classify minerals? By the principle negative ion in their chemical composition Example: Calcite and dolomite are both carbonates Calcite is CaCO3 Silicates are a very important class of minerals, as they make up the major rock-forming Physical Properties Luster Is it metallic or non-metallic? How does it reflect light? Streak The color of the powder when scratched on unglazed porcelain. Hardness A fingernail has a hardness of 2.5 A glass plate has a hardness of 5.5 If you can’t scratch the mineral, and it won’t scratch glass, it has a hardness between 2.5-5.5. Fracture When a mineral breaks in an irregular manner, like when glass breaks. Minerals can’t have both fracture and clevage. Cleavage Minerals break along zones of weaker chemical bonds. Example: 1 direction of cleavage (called basal) in a mica mineral - it peels off in sheets. Specific Mineral Info Calcite - reacts with acid - best way to identify it. Pyrite - has metallic luster - ‘fools gold’ How do you tell quartz from calcite? They are both often clear. Hardness - (quartz scratches glass, calcite won’t), Acid test (Calcite will fizz, quartz won’t), Shape (Calcite forms rhombohedrons and quartz hexagonal prisms), and Cleavage (Quartz has none, calcite has 3 directions) Unit 4 Midterm Review Igneous Rocks Form from the solidification of a melt; Can happen inside of the Earth’s surface or if it’s erupted out of a volcano Classified by their silica content Their silica content determines the behavior of lava flow. Texture - tells you about cooling history Phaneritic - Coarse-grained Minerals you can see Later erosion brings it to the surface Slow cool underground Aphanitic Fine-grained You can’t see the minerals Fast cool above ground Vesicular Vesicles - Holes where gas bubbles were Cooling History A phaneritic rock cools slowly within the earth (intrusive). This results in a coarse-grained texture. As the melt formed slow enough for larger crystals to form. Some examples are granite, diorite, and gabbro. An aphanitic rock cools quickly outside the earth (extrusive). This results in a fine-grained texture, as the melt cools so fast that the minerals didn’t grow to a size you can see. Some examples are rhyolite, andesite, and basalt This chart shows how elements come together to form particular minerals at a specific range of temperatures as a melt crystallizes. Which mineral would crystallize first? Olivine Which mineral would you find in granite, a felsic igneous rock? Quartz, Muscovite, Feldspar Specific Igneous Rocks Diorite - Composed mostly of amphibole and plagioclase, intermediate Obsidian - Known for glassy texture Basalt - Mafic in composition Volcanoes! Viscosity = resistance to flow High viscosity = harder to flow - must be forced out of the volcano. Explosive volcanic eruptions do NOT produce extensive lava flows Low Viscosity = flows well - ex. Basaltic lavas Effusive eruptions are characterized by lower viscosity magmas. Dormant is a term given to volcanoes that are not currently erupting, may not have for a long period, but will erupt again. Some Volcano Types Cinder Cones - Erupt only once Supervolcano - Has had a MAJOR eruption - name based on size of eruption, NOT on times it has erupted Some Volcano Settings Mid-ocean Ridges - Cover 70% of Earth’s surface; basalt comp. More Volcano Info Mt. Shasta, in northern California (part of the Cascades) will erupt andesitic in composition. Earth’s largest mass extinction is associated with 2 million year volcanic eruptions which build the Siberian traps (flood basalt) Flood basalts are extrusive - they erupt above ground Unit 5 - Sedimentary Rocks How they form Loose material breaks off from pre-existing rock to make smaller pieces. (Gravel, salt, silt, clay) Minerals precipitate from solution Organisms die and their shells accumulate on the seafloor Heating and cooling are NOT involved in their formation Physical Weathering Produces clasts Classified based on size- decreasing size range Pebble-Sand-Silt-Clay Compaction: Creates a sedimentary rock by removing the spaces between the grains Frost wedging is an example of physical weathering. Chemical Weathering Minerals precipitate from a solution The texture of a chemical sedimentary rock is crystalline Dissolution and hydration are exs of chemical weathering Hydrolysis occurs when water reacts chemically with minerals to break them down. Clues to Environment In clastic rocks, you can determine how close you are to the source rock based on: Grain size - larger grains are closer to the source Angularity/Sphericity - angular grains are closer to source Sorting - more poorly sorted closer to source Clastic rocks - relationship between grain size and depositional environment Conglomerate - pebble-silt; high energy; streams Breccia - pebble-silt high energy; alluvial fan Sandstone - sand; mid-energy; beach or desert Shale - silt-clay; low energy; lake or ocean bottom A river is a depositional environment where you can deposit gravel, sand, silt, and mud due to the changing energy that rivers have. A desert would most likely produce a pure quartz sandstone. Sedimentary Structure Mud cracks form when wet fine-grained sediment dried out (it gets wet, then dried) Ripple marks form as a result of wind or water currents. A Conglomerate is a rock that has a range of grain sizes- from silt to pebble size Coal is an example of an organic sedimentary rock Soils form from the physical and chemical interaction of rock material with: Organic matter Rain Organisms Unit 6 Metamorphic Rocks These rocks are buried, and heat and pressure are applied to pre-existing rock to change them. Rocks experience grades of metamorphism - low, medium, high Rocks that undergo high grade metamorphism would be buried very deeply (example - gneiss) When a rock experiences plastic deformation, this is associated with differential stress The types of stress that act on these rocks are: Compressional, Tensional, Shear Some Metamorphic Terms Neocrystallization - Refers to the growth of new minerals as a result of metamorphism. Recrystallization - Refers to the change in size and shape of mineral grains during metamorphism. Phase Change - The transition of 1 mineral to another with the same composition, but different crystalline structure. Metamorphic Rocks Slate - The finest grained metamorphic rock; low grade Schist - Forms at intermediate grade metamorphism; “Shiny chist” - has a glittery appearance due to the micas; its protolith is shale Gneiss - forms at high grade metamorphism An example of a non-foliated metamorphic rock is quartzite, which is coarse-grained and has a quartz sandstone for its protolith Marble - A non-foliated metamorphic rock that reacts to acid. Migmatites are formed when temperatures get high enough to melt the felsic materials in a rock, but not the mafic ones. Has separated bands of light and dark color A Porphyroblastic texture has large minerals A gneiss will have gneissic banding. Quartzite and marble can be confused. How do you tell them apart? Hardness - quartzite scratches glass Acid Test - Marble fizzes, quartzite will not. Types of Metamorphism Dynamic - high pressure impacts; asteroid crater. Regional - involves a region; large scale mountain building. Contact - Involves proximity to an igneous intrusion.