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Transcript
UNIT 7 Notes: The Forces the Effect Earth Earth’s Interior The Science of Geology Geology is the study of planet Earth. Scientists that study the forces that make and shape Earth are called geologists. Geologists study the chemical and physical characteristics of rock. Studying Surface Changes There are two forces that change Earth’s surface features: 1.Constructive forces: shape the surface by building surface features. (To help remember constructive forces, think about a construction site. At a construction site they are building buildings, so constructive forces build surface features.) Destructive forces: slowly wear away surface features. (To help remember destructive forces, think about the word destroy. Destructive means to destroy features. Indirect Evidence-Seismic Waves Geologists are not able to travel to the center of Earth because the temperature is too hot and the pressure is too great. Geologists must relay on other evidence to study the Earth’s interior. Geologists study how seismic waves travel through the Earth to identify the layers of the Earth. Seismic waves travel faster through solids and slowest through gases. By measuring seismic waves speed, geologists can determine the interior of the Earth. A Journey to the Center of Earth Temperature and pressure both increases from the surface to the center. The Earth has three main parts: 1. The crust is a layer of rock that forms Earth’s outer skin. There are two types of crust basalt (the crust under the ocean) and granite (the crust under the continents), -Basalt is a dark, dense rock making the oceanic crust. -Granite is a light-colored rock with large crystals making continental crust. 2. The mantle is a layer of hot rock between the crust and core. The lithosphere is a rigid layer that includes the upper mantle and the crust. The astenosphere is a soft layer just below the lithosphere in the mantle 3. The core is made of iron and nickel. The core is two parts, the outer core and inner core. - Outer core: a layer of molten metal surrounding the inner core. - Inner core: a dense ball of solid metal Earth’s Magnetic Field The rising and sinking of the hot liquid metal in the outer core creates convection currents. Convection currents in the liquid outer core force the inner core to spin faster than the rest of Earth creating Earth’s magnetic field. Convection Currents and the Mantle Heat transfer is the movement of energy from a warmer object to a cooler object. Three types of heat transfer: – Conduction – Convection – Radiation • Conduction: heat transfer by direct contact • Convection: heat transfer by the movement of a heated fluid. Convection is caused by temperature and density differences. – Density: how much mass there is in a volume of a substance. – Increasing temperature decreases density Convection Currents: Circular motion of fluid caused by the rising and sinking of heated and cooler fluid • Radiation: energy transfer by electromagnetic waves. Convection in Earth’s Mantle Heat from Earth’s core and from the mantle itself causes the convection currents in the mantle. Drifting Continents Continental Drift In 1910, Alfred Wegener hypothesized that all the continents were once adjoined and have since drifted apart. Pangaea: super continent. Continental drift: continents slowly moved over Earth’s surface. Evidence of Continental Drift Landforms Example: South Africa and Argentina mountains align Example: Europe and North America coal fields align Fossils: traces of organisms preserved in rock Similar fossils located on different continents Climate The climate of specific locations has changed because the position of these places on Earth’s surface changed. Geologists in the early 1900s did not accept Wegener’s hypothesis. Wegener could not provide a satisfactory explanation for the force that pushes or pulls the continents. Sea-Floor Spreading Mid-Ocean Ridge Mid-Ocean Ridge: longest mountain chain in the world The top of the mid-ocean ridge is split by a steep-sided valley. Sea-Floor Spreading: the process of adding new material to the ocean floor. Evidence for Sea-Floor Spreading Magnetic stripes Ocean floor rock lies in patterns of magnetized strips. Drilling samples The Glomar Challenger took samples of rock. The farther from the ridge, the older the rocks. Subduction at Deep-Ocean Trenches Deep-ocean trenches: downward bend in the oceanic crust Subduction: the process of the ocean floor sinks beneath a deep-ocean trench and back into the mantle. Gravity pulls the older, less dense oceanic crust beneath the trench. Subduction and Earth’s Oceans Pacific Ocean Shrinking because the many trenches swallows more oceanic crust than produced. Atlantic Ocean Expanding because it only has a few short trenches. The Theory of Plate Tectonics A Theory of Plate Motion Plates: separate broken sections of the lithosphere. Plate tectonics: theory that pieces of Earth’s lithosphere are in constant, slow motion, driven by convection currents in the mantle. – Explains formation, movement, and subduction of Earth’s plates. Plate Boundaries Plate boundaries: lines where pieces of lithosphere meet Faults: breaks in Earth’s crust where rocks have slipped past each other. Transform boundaries: two plates move past other in opposite directions – Earthquakes Divergent Boundaries: Two plates move apart – Ocean Mid-Ocean Ridge – Land Rift valley: a deep valley formed at divergent boundaries on land The Continents’ Slow Dance Convergent boundaries: Two plates move together – Collision results Density determines the top plate Oceanic/oceanic plates –subduction occurs Oceanic/continental–oceanic plate sinks. Continental/continental– mountain ranges form Plates move about 1 to 10 cm per year. Changing Earth’s Surface Forces in the Lithosphere Plate movements produces stress in rock. – Stress adds potential energy to the rock until it changes shape or breaks and moves. – Stress leads to deformation ( a change in the rock’s shape or volume). Forces in the Lithosphere 3 types of deformation – Shearing: rock slips in opposite directions – Tension: pulls rock – Compression: pushes rock together Fault Movements Faults usually occur along plate boundaries (where lithosphere breaks). – Strike-Slip Faults: rock on either side of the fault slip past each other sideways. – Normal Faults: fault is at an angle Hanging wall: half of the fault above Footwall: half of the fault below – Reverse Faults: formed by compression forces and blocks toward each other Mountain building caused by: Folding Plates collide Faulting Fault-block mountains: blocks of crust slid along normal faults to form mountains Land Subsidence Land subsidence occurs when land surface sinks as a result of geologic processes or human activities. – Plate movements can cause the formation of rift valleys and ocean basins. – As uplift raises one part of the crust, land subsidence occurs in an adjoining area. Volcanic Mountains Volcano: a weak spot in the crust where molten, rock-forming magma comes to the surface. Volcanic activity builds mountains made of lava rock and other volcanic materials. Locations of Volcanoes Diverging Plate Boundaries – Rift Valley – Mid-Ocean Ridge Converging Boundaries – Subduction occurs Hot Spot Volcanoes – An area where magma from mantle melts through the crust