Intro to Geology Notes
Intro to Geology Notes GEOL 201- 002 (, Lori D. Snyder)
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This 8 page Class Notes was uploaded by Leah Notetaker on Monday September 26, 2016. The Class Notes belongs to GEOL 201- 002 (, Lori D. Snyder) at University of Wisconsin - Eau Claire taught by `Lori D. Snyder in Fall 2016. Since its upload, it has received 161 views.
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Date Created: 09/26/16
Geology Notes (Introduction of National Parks – Half-Life) Administration of Federal Lands The U.S. was the first country to put the mechanism of preserving public land. This idea was not established until the late 1800’s and done on mostly western land due to the eastern land being mostly settled. History of U.S. National Parks 1807- John Colter, part of the Lewis and Clark Expedition, passes through what is now Yellowstone National Park. 1870- Judge Cornelius Hedges, part of the Henry Washburn Survey Party, put forth idea of preserving land for future generations. (Credited, but may be fable.) 1871- Congress sends expedition with geologist Frank Hayden to investigate. National Park Designation Creation requires an act of Congress. Yellowstone was made a national park on March 1, 1872 under President Ulysses S. Grant. The 1906 Antiquities Act authorized presidents, starting under Theodore Roosevelt, to proclaim “historic landmarks, historic or prehistoric structures, and other objects of historical or scientific interest” as national monuments. (ex. Grand Canyon, Devil’s Canyon) The Early Years (1872-1916) National Parks were created but not protected. Thermal features were damaged, and bison were nearly extinct due to over hunting. A hydroelectric dam was built in Yosemite after the San Francisco earthquake. In 1916, a businessman, Steven Mather, urged U.S. Congress to create the National Park Service. In 1977, the Clean Air Act was passed. The air quality in 156 areas designated Class 1 must be monitored and maintained. Administration The president oversees the Department of Agriculture and Department of Interior Affairs. The Department of Inter. Oversees the U.S. Fish and Wildlife Service, the Bureau of Land Management, the National Park Service, and the Bureau of Indian Affairs. The National Park Service oversees 58 National Parks and 340 other areas. The Department of Agriculture oversees the U.S. Forest Service. BLM, USFWS, and USFS use the multiple use philosophy, where anybody may use the land for recreational purposes. The National Park Service and BIA, however, do not, and permission is often needed ahead of time to visit the land/ use it for recreation. Earth Materials Rocks are made up of minerals. Minerals are the building blocks of rocks. Minerals are naturally occurring, inorganic, crystalline solids, have distinct chemical composition, and a unique set of physical properties (structured order). Earth’s crust is made of 75% silicon and oxygen, mainly making up quartz. Other materials include aluminum, iron, calcium, sodium, potassium, magnesium, and small amounts of others. Common Silicate Minerals Silica- rock which contains silicon and oxygen (ex. quartz, feldspar, olivine) Carbonate Minerals Are the largest reservoir of carbon on the planet, and their formation (in chemical sedimentary chemical rocks) plays a role in global climate; found in oceans, rocks and sediments, biospheres, fossil fuels, etc.) Neutralizes acid Ex. Calcite Three Basic Types of Rocks The Type and Name of a Rock is determined by o Composition (what the rock is made of) o Texture (how the rock is made up) Texture has two types: interlocking and clastic Igneous Rocks Crystalize from molten material; magma when below surface, lava above Magma forms in certain plate tectonics Igneous intrusive rocks form inside of the Earth and cool slowly and form large grains Igneous extrusive rocks form outside of the Earth and cool quickly and form small grains Interlocking texture- minerals in rock are intergrown with one another o Coarse grained- components of rock large enough to be seen with unaided eye (intrusive) o Fine grained- components too small to be seen with unaided eye (extrusive) Sedimentary Rocks Formed when rocks are exposed on Earth’s surface; weathering, erosion, deposition, burial, and lithification Particles of weathered rock are called sediment or detritus Formed from the compaction and cementation of fragments of pre- existing rocks/minerals Clastic texture- components cemented together, usually by quartz Chemical Sedimentary Rocks- form from precipitated minerals out of water Evaporite- mineral precipitated from evaporation of water (ex. Gypsum, Halite) Carbonate minerals are precipitated organically or inorganically from sea water and are common in the rock record Geometry and Features of Sedimentary Rocks Form in layers or beds on Earth’s surface. Different characteristics of beds indicate changes in environmental condition. Features record conditions of time and place. Characteristics of sediment, sedimentary structures, and fossils help geologists determine the environment at the time. Metamorphic Rocks Formed by any changes in any rock type resulting from increased pressure and temperature Show changes in minerology and texture Form from recrystallization of pre-existing rocks due to elevated heat/pressure o Regional metamorphism occurs over large areas over time (ex. mountain ranges) o Contact metamorphism occurs from local heating without deformation Often foliated- minerals are aligned during growth under directed stress (ex. gneiss) Metamorphic rocks are used to study temp., pressure, and chemistry of Earth’s interior 92% of Earth’s crust is igneous or metamorphic, but 75% of the surface is sedimentary. Earth’s Interior Composed of minerals and elements Whole Earth mostly made of iron, silicon, and oxygen. The crust is mostly made of silicon and oxygen. Different levels of silica composition o Ultramafic: <45% SiO2, dark in color, very high density o Magic: 45-52% SiO2, dark in color, high density o Intermediate: 52-66% SiO2, mixture of color, medium density o Felsic: >66% SiO2, light color, low density The lower the levels of SiO2, the more materials that are in there, and heavier the materials. (Ex. iron, very heavy) Layers of the Earth Seismic waves in earthquakes show us that the Earth has layers. Two types of waves. o P-waves- also called compressional or primary; try to change material volume, run parallel o S-waves- also called shear or secondary; try to change material shape, waves run up and down o P-wave are faster than s-waves. o No s-waves in the outer core because outer core is liquid. The Core has a solid iron inner core and a liquid outer core. The Core is mostly composed of Iron and Ni. The Core is important because it deflects a lot of solar radiation. The Mantle is ultramafic, so it is heavy and solid. Mostly Fe, Mg silicates The lower mantle is called the Mesosphere. The Asthenosphere is ductile; somewhat gooey, “soft solid”. Makes the grains slide and makes plate tectonics possible. It is not molten. The Lithosphere, above the asthenosphere, has the crust and the solid part of the mantle, and is what causes volcanoes and earthquakes. Two Types of Crust Continental: 25-60 km thick, felsic rock composition, lower density, crust older Oceanic: 5-8 km thick, mafic rock composition, higher density, younger crust Plate Tectonics Geologic process created due to movement of Earth’s lithospheric plates. Responsible for the distribution and types of volcanoes, mountain ranges, earthquakes Came from Mid-Ocean Ridge, which covers 20& of Earth’s surface Volcanic activity happening; mafic Plate Boundaries Divergent- plates move away Convergent- plates move apart Transform- plates move past each other Divergent Plate Boundary: Continental Rift Rift- linear zone where Earth’s lithosphere is being pulled apart. Valley often formed and the feature is an example of extensional tectonics. Asthenosphere moves up, undergoes decompression melting under low pressure (ex. Basin and Range) Extensional Tectonics A rift and valley are formed Oceanic crust created from mafic volcanism In time, edges of continents become passive margins Passive Margins- transition between oceanic and continental lithosphere which is not tectonic plate boundary (ex. Colorado Plateau) Divergent Plate Boundary: Sea Floor Spreading Very mafic Lithosphere sinks, ocean comes in (ex. Baja) Convergent Plate Boundary: Ocean-Continent Subduction Zone Subduction- where oceanic lithosphere forced below the mantle of the continental plate; causes volcanoes (ex. Ring of Fire) Creates volatiles, which are hot fluids. Released volatiles cause the mantle to melt. Makes magma, an intermediate composition. Some materials will not go into the trench, will create a coastal mountain range, or accretionary wedge (ex. Pacific Northwest, Cordillera Range) Continent-Continent Convergence Ocean closes and continents collide Hot Spots: Oceanic and Continental Hot places in mantle that the process of heat transfer melts materials on top of them Liquid to solid: thermal energy, goes into plumes. Very large, circular in pattern. Creates volcanoes. (ex. Hawaii, Samoa, Yellowstone) Geologic Time Origin of Earth is at the bottom layers, latest years on top. Developed in the 19 century by James Hutton using relative dating techniques Numbers were not added until the early 20 century using absolute dating techniques. Relative dating- older or younger? Absolute dating- exact age Methods of Dating Principle of Uniformitarianism- “the present is the key to the past”; processes operating on Earth today operated the same in the past Principle of Fossil Succession- plant and animal fossils are relative to time Principle of Original Horizontality- rocks are deposited as horizontal layers Principle of Superposition- each layer of rock in an undisturbed sequence is younger than the layer below it Cross-Cutting Relationships- igneous intrusions and faults are younger than the rocks that they intrude or break o Fault- a break in the rocks o Inclusions- if a rock is completely enclosed by a different rock, the piece (inclusion) is older Unconformity A surface between two rock units of different ages that represents a period of erosion, breaks in the rock record Classified and recognized based on rock type and the relationship of geologic units o Nonconformity- rocks below the unconformity are metamorphic or igneous intrusive while rocks above are sedimentary or igneous extrusive o Angular Unconformity- rocks below unconformity are folded or faulted while ones above are not o Disconformity- rocks above and below the unconformity are horizontal and not deformed; often requires fossil evidence to recognize this Constructing a Geologic History A list of geological events, generally listed from oldest to youngest that can be determined for an area. Events include: rock formation, folding/faulting, and unconformities Absolute Ages Numbers were added to the geologic time scale using radioactive decay Radioactive decay- unstable isotopes spontaneously turn into more stable isotopes Atomic number- the number of protons in an element; the number of protons cannot change, but the number of electrons can (make ions) and so can neutrons (change atomic mass) Isotopes are atoms with different atomic mass- a different number of neutrons (ex. Carbon-12, Carbon-13, Carbon-14) Radiometric Dating Parent Material- original unstable isotope Daughter Product- secondary stable isotope Half-Life- amount of time it takes for one-half of the parent material to decay to daughter product Radioactive decay proceeds at a known rate, therefore scientists can measure how long it takes for ½ of a group to do it. Ex. Solar radiation strikes Nitrogen-14 in the atmosphere, neutron captures, creates Carbon-14. Plants and animals take in carbon and are made up of it. When they die, the carbon decays. It eventually changes back into Nitrogen-14. Carbon-14 is NOT used for dating rocks. Measuring Isotopes Decay rate is constant. Closed system. (No material gained or lost) Daughter product is result of radioactive decay of parent materials. Our analytical methods are correct. Mass spectrometer is the tool often used to measure this, where a magnetic field separates particles based on the mass to charge ratio. Half-Life Examples Uranium to Lead = 4.5 billion years Rubidium to Strontium = 47 billion years Potassium to Argon = 1.3 billion years Carbon to Nitrogen = 5730 years
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