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Geology – Part II Earth’s Interior, Plate Tectonics, Earthquakes, Volcanoes & Earth’s History Earth’s Interior 1.Earth’s interior is divided into the: a. Crust b. Mantle c. Outer core d. Inner core surface center of earth 2. The lithosphere includes the crust and the rigid upper layer of the mantle. 3. The Asthenosphere lies below the lithosphere and is made up of the soft layer of the mantle. Earth’s Interior Plate Tectonics 1. Plate – lithosphere is broken into separate sections called plates 2. Alfred Wegener developed the idea that the continents were once joined and have since drifted apart. The once giant land mass was known as Pangaea. 3. The Theory of Plate Tectonics explains the plate constant, slow motion, driven by convection currents in the mantle. It combines the theories of continental drift and sea-floor spreading. Plate Tectonics a. Plates move in the following ways: i. Transform Boundaries - slip past one another/No change in elevation (stress = shearing) ii. Divergent Boundaries - move apart/may cause a change in elevation (stress = tension) iii. Convergent Boundaries - come together/may cause a change in elevation (stress = compression) Plate Tectonics/Plate Boundaries Diverging Plate Boundary Converging Plate Boundary Transform Plate Boundary Earthquakes A. Description 1. An earthquake is the shaking and trembling that results from the movement of rock beneath Earth’s surface 2. Earthquakes occur because of stress built up in rock. Stress is a force that acts on a rock to change its shape or volume. These stresses cause faults (a break or crack in Earth’s lithosphere (underground) along which the rocks move). There are three types: a. Shearing – Strike-slip Fault b. Tension – Normal Fault c. Compression – Reverse Fault Plate Tectonics & Faults Tension Normal Fault Compression Earthquakes B. Measuring Earthquakes 1. Seismic Waves – vibrations that travel through Earth carrying the energy released by an earthquake. a. Primary Waves – P waves arrive first move by compression and expansion b. Secondary Waves – S waves arrive second - move side to side and up and down c. Surface Waves – when P and S waves meet the surface – move in different directions 2. Epicenter – center of the earthquake ON Earth’s surface; in order to find the epicenter of an earthquake, you need data from 3 cities Earthquakes C. Earthquake Hazards 1. Soil Conditions/Shaking 2. Liquefaction – violent shakes turn loose, soft soil into mud 3. Aftershock – earthquake that occurs after a big earthquake in the same area 4. Tsunamis – large wave caused by an earthquake on the ocean floor D. Earthquake Safety 1. 2. 3. Location – some places are more prone to earthquakes Construction – earthquake-proof buildings/houses (base-isolated buildings) Drop, cover and hold E. Earthquake Detecting Devices – 4 fault monitoring devices 1. Creep Meters – uses a wire across a fault to measure horizontal movement of the ground 2. Laser-ranging Devices – uses a laser to measure horizontal movement 3. Tiltmeters – measures tilting or raising of the ground 4. Satellite Monitors – uses GPS from outer space to monitor changes in elevation as well as horizontal movement along a fault 5. Seismographs – collects data (seismic waves) from earthquakes Volcanoes A. Description 1. A volcano is an opening in Earth’s Surface where magma escapes from the interior. Magma is the liquid inside a volcano. When magma reaches earth’s surface it is called lava. 2. Most volcanoes occur near the boundaries of Earth’s Plates and along the edges of continents above subduction zones, in island arcs, or along mid-ocean ridges (under water mountain ranges) Earthquakes & Volcanoes Volcanoes B.Volcanic Landforms 1. Shield Volcanoes – Hawaiian Islands; quiet eruptions, lava flows, wide base, not very tall 2. Cinder Cone Volcanoes – Paricutin in Mexico; explosive eruptions of cinders/rock/gases – tall, narrow base 3.Composite (Strato) Volcanoes – alternating quiet/explosive eruptions – alternating layers of lava and ash; Mt. Hood, Mt. St. Helen’s, Mt. Ranier Volcanoes C. Volcano hazards 1.Pyroclastic flows 2.Damage from ash 3.Lava Flows 4.Avalanches of mud 5.Flooding 6.Deadly gases Volcanoes D.Volcano Benefits 1. Fertile Soil 2. Increased Tourism 3. Energy source Historical Geology A. Measuring Time 1. Relative Time (Relative Age) – Measurement of time using comparison. No numbers used; uses words like younger and older. a. Example – Joe is older than Mike 2. Absolute Time (Absolute Age) – Measurement of time using actual numbers a. Example – Mike is 15 years old Historical Geology continued B. Measuring Earth’s Age (Relative Time) 1. Many Paleontologists use rock layers a. Fossils are mainly found in sedimentary rock. b. The layers help tell the relative age of rocks c. The LAW OF SUPERPOSITION states that oldest layers of rock are on the bottom and younger layers are on the top. Historical Geology continued • Unconformity – eroded rock surface pushed up from deeper within earth that is much older than the new rock layers above it. • Glacial Till – large buildup of rock pieces carried away in the bottom of a glacier • Kettle Lake – lake formed when a large block of glacial ice melts leaving a depression in the ground. • Drumlins – long, smooth, canoe shaped hills made of glacial till • Peat – substance made of decayed plant fibers, softest type of coal Historical Geology continued 2. Faults can be used to help determine the relative age of a rock layers and the order in which events happened. a. A rock layer had to occur before a fault can occur. b. Younger features cut across older features – this is called CROSSCUTTING RELATIONSHIPS 3. A fault is a break or crack in part of Earth’s crust. 4. UNCONFORMITY – a break in the rock record that separates series or layers of deposits. a. Layers that are exposed above sea level are often times eroded away with brand new layers being deposited above the erosion mark. Historical Geology continued C. Determining Absolute Age 1. Radioactive Dating a. The breaking down of atoms to form different isotopes of the same element or a completely new element Carbon-14 Carbon-12 b. Energy is given off in the form of - Gamma Rays - Alpha Particles - Beta Particles Historical Geology continued 2. Half-Life a. The amount of time it takes for half of the original atom to decay 1. Uranium-238 = 4.5 billion years 2. Carbon-14 = 5,700 years 3. Oxygen = 19 seconds b. In the amount of time give (half-life time), half of the original substance will be gone. Historical Geology continued c. Example: If we start with 20 grams of carbon14, how long will it take to break down to 5 grams Start of 0 years 5700 years 11, 400 years = = = 20 grams 10 grams 5 grams As you move down the left hand side of these equations, keep ADDING THE HALF-LIFE AMOUNT. As you move down the right hand side of these equations, divide by 2 (take half!) Historical Geology continued Fossils A. Description - Any remains or evidence of a living thing B. Types 1. 2. 3. 4. 5. 6. Shells Bones Pollen/Grains Seeds Imprints Molds & Casts Historical Geology continued C. Formation of Fossils 1. Preservation without change a. Frozen plants or animals/objects stuck in amber (pine tree sap/resin) or tar 2. Replacement by a mineral a. Material decays and is slowly replaced by a silicate (petrified wood) Historical Geology continued 3. Formation of a carbon film a. As material decays a carbon film is left behind 1. Used only with living things 2. Used with half-life 4. Formation of an imprint – mold 5. Filling of an imprint – cast D. Index Fossils – special marker used by geologists to identify layers of rock that are separated far apart. Geologic Time A. Divisions 1. Eras – largest division of geologic time a. Pre-Cambrian *** can be broken down into eons*** b. Paleozoic c. Mesozoic d. Cenozoic Geologic Time 2. Periods – subdivision of an era a. Paleozoic Era – age of the invertebrates 1. Cambrian Period 2. Ordovician Period 3. Silurian Period 4. Devonian Period 5. Carboniferous Period – broken down into Pennsylvanian & Mississippian in North American only 6. Permian Period - ** The trilobite died out at the end of the Permian Period, marking the end of the Paleozoic Era Geologic Time b. Mesozoic Era – age of the reptiles/dinosaurs a. Triassic Period b. Jurassic Period c. Cretaceous Period ** The dinosaurs died out at the end of the Cretaceous Period, marking the end of the Mesozoic Era Geologic Time c. Cenozoic Era – age of the mammals 1. Tertiary Period 2. Quaternary Period ** Epoch – division of geologic time that occurs only in the Cenozoic Era; breaks down periods into smaller chunks of time ***CENOZOIC ERA, QUATERNARY PERIOD ARE STILL GOING ON NOW!!!!