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Chapter 1 An Introduction to Geology and Plate Tectonics PowerPoint Presentation Stan Hatfield . Southwestern Illinois College Ken Pinzke . Southwestern Illinois College Tark Hamilton . Camosun College Copyright © 2009 Pearson Education Canada 1-1 The Science of Geology Geology is the science that pursues an understanding of planet Earth • Physical geology - examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface • Historical geology - seeks an understanding of the origin of Earth and its development through time Copyright © 2009 Pearson Education Canada 1-2 The Science of Geology Geology, people, and the environment • There are many important relationships between people and the natural environment • Some of the problems and issues addressed by geology involve natural hazards, resources, world population growth, and environmental issues Copyright © 2009 Pearson Education Canada 1-3 The Science of Geology A Canadian Profile • Sir William Edmond Logan has been called Canada’s #1 scientist in history • He was the first director of the GSC and was active in the outdoor pursuits of geology Copyright © 2009 Pearson Education Canada 1-4 The Science of Geology Some historical notes about geology • The nature of Earth has been a focus of study for centuries • Catastrophism: shaping of the Earth’s landscape by rare catastrophes • Uniformitarianism: a principle first proposed by James Hutton that represented the Birth of Modern Geology (processes that operate today also operated in the past; Gradualism + Vast Time) Copyright © 2009 Pearson Education Canada 1-5 Geologic Time Relative dating and the geologic time scale • Relative dating means that dates are placed in their proper sequence or order without knowing their age in years (apply Principles of Superposition and Fossil Succession) Geologists are now able to assign fairly accurate dates to events in Earth history • Absolute radiometric dating means that particular isotope clocks determine exact ages Copyright © 2009 Pearson Education Canada 1-6 Geologic Time The magnitude of geologic time • Involves vast times – millions or billions of years (the Earth is 4.6 billion years old!) • An appreciation for the magnitude of geologic time is important because many processes are very gradual (name some? Copyright © 2009 Pearson Education Canada 1-7 Geologic Time The Geologic Time Scale. The numbers are absolute ages in millions of years before present. Note that the Precambrian accounts for 88% of geologic time and yet the Phanerozoic with its wealth of fossils includes many divisions (Eras, Periods, Epochs). Copyright © 2009 Pearson Education Canada 1-8 Early Evolution of Earth Origin of planet Earth • Most researchers believe that, following the Big Bang, The Solar System: Earth and the other planets formed at essentially the same time from the same primordial material as the Sun • Nebular hypothesis Layered structure developed by chemical segregation early in the formation of Earth (Differentiation) Copyright © 2009 Pearson Education Canada 1-9 The Nebular Hypothesis Copyright © 2009 Pearson Education Canada 1-10 Plate Tectonics: a geologic paradigm • Provides modern geologists with the first comprehensive model of Earth’s internal workings (Convection, Heat Loss) • Began in the early part of the twentieth century with a proposal called continental drift – the idea that continents moved about the face of the planet and "drifted" to present positions • Sea Floor Spreading was post WWII from seismology and ocean mapping Copyright © 2009 Pearson Education Canada 1-11 Plate Tectonics Alfred Wegener and continental drift • First proposed his continental drift hypothesis in 1915; an idea before its time • Published The Origin of Continents and Oceans Continental drift hypothesis • Supercontinent called Pangaea began breaking apart about 200 million years ago Copyright © 2009 Pearson Education Canada 1-12 Plate Tectonics Pangaea approximately 200 million years ago. Copyright © 2009 Pearson Education Canada 1-13 Plate Tectonics Evidence used in support of the continental drift hypothesis • Fit of the continents: Africa-S. America • Fossil evidence: Glossopteris, Mesosaurus • Rock type and structural similarities • Paleoclimatic evidence: S. Hemisphere Late Paleozoic glaciation (places now hot) Copyright © 2009 Pearson Education Canada 1-14 Plate Tectonics Wegener’s matching of mountain ranges on different continents. Lithologies, Mountain Belts & Orogenies Match across Atlantic Appalachians = Caledonides = Svecofennides, Devonian Granites Copyright © 2009 Pearson Education Canada 1-15 Plate Tectonics Paleoclimatic evidence for continental drift. Late Paleozoic reconstruction of Pangea puts ice over Antarctica, S.Pole Modern position of icy facies near Equator! Copyright © 2009 Pearson Education Canada 1-16 Mesosaurus teniudens: (Faunal ties Pangea) Early Permian Period (286 to 258 Ma) Irati Formation, Brazil Namibia, Africa Copyright © 2009 Pearson Education Canada 1-17 Glossopteris: (Floral ties Pangea) Early Permian Period (286 to 258 Ma) Gloss. browniana Distribution of Gloss. & Vertebraria Copyright © 2009 Pearson Education Canada 1-18 Planet of Shifting Plates Plate boundaries (3 types) • All major interactions among individual plates occur along their boundaries • Divergent boundary – two plates move apart, resulting in upwelling of material from the mantle to create new seafloor between them • Convergent boundary – two plates move together with subduction of oceanic plates or collision of two continental plates, ocean crust is recycled • Transform boundary – two plates slide laterally past each other (rotation) Copyright © 2009 Pearson Education Canada 1-19 Planet of Shifting Plates Brittle cold rigid Lithosphere plates slide over warm plastic Upper Mantle Thermal convection in Mantle at a few cm/year is the driver Mosaic of rigid lithospheric plates and divergent and convergent boundaries. Copyright © 2009 Pearson Education Canada 1-20 Planet of Shifting Plates Plate boundaries • Transform fault boundaries - located where plates slide past each other without either generating new lithosphere or consuming old lithosphere • These are the fracture zones of Mid Ocean Ridges • Others cut Contintents or are Continent Ocean Boundaries: Anatolian, Queen Charlotte, San Andreas, Alpine Fault NZ Copyright © 2009 Pearson Education Canada 1-21 Planet of Shifting Plates Mosaic of rigid plates and a transform fault boundary. Copyright © 2009 Pearson Education Canada 1-22 Earth’s Internal Structure Earth’s internal layers can be defined by • Chemical composition (Different Rock Types) • Physical properties (Brittle, Plastic, Liquid, Solid) Layers defined by composition • Crust: SIAL - Granodiorite • Mantle: SIMA - Peridotite • Core: Fe-Ni – like Meteorites: Copyright © 2009 Pearson Education Canada 1-23 Earth’s Internal Structure Four main layers of Earth are based on physical properties and hence mechanical strength (heat content, pressure & composition) • Lithosphere: rigid • Asthenosphere: weak, plastic, few% partial melts • Mesosphere (or Lower Mantle) weak plastic entirely solid • Outer Core: 100% molten • Inner Core: 100% solid Copyright © 2009 Pearson Education Canada 1-24 Earth’s Internal Structure Views of the Earth’s layered structure. Copyright © 2009 Pearson Education Canada 1-25 Earth as a System The Earth system is powered by the Sun that drives external processes in/on/above the • Atmosphere • Hydrosphere • Cryosphere • Lithosphere (Earth’s Surface) How long do cycles take to modify each? Copyright © 2009 Pearson Education Canada 1-26 System Science View of Earth & Cycles Earth is a planet that is small and self-contained, all matter is conserved & recycled Earth’s four conceptual spheres & cycles • Hydrosphere: daily-annual evaporation & precipitation • Atmosphere: daily-annual-long term changes • Cryosphere: Ice caps, glaciers, sea ice, permafrost • Biosphere: How far does this extend? • Geosphere: The Solid Earth as in the last slides. Tectonic “Wilson Cycles” last ~500 Ma • Climate isEducation the long Copyright © 2009 Pearson Canada term interplay of all these!1-27 Cryosphere: Ice Crystals with Hydrogen Bonding Red negative ends of the water molecule attract Green positive ends forming hexagonal ice Copyright © 2009 Pearson Education Canada 1-28 Greenhouse Gases Warm the Earth’s Exterior: H2O , CO2 , O3 , CH4 , SOx , NOx Any molecular gas that absorbs thermal (infra-red) radiation is a greenhouse gas. Mainly asymmetric molecules and ones with resonant bonds Predominant N2 and O2 are transparent to heat (short strong multiple bonds) Copyright © 2009 Pearson Education Canada 1-29 Bill Comes Ashore at Peggy’s Cove, NS What “Spheres” does this involve? What Global Cycles does this involve? Copyright © 2009 Pearson Education Canada 1-30 A View of Earth: Observations ~ Scale The breathtaking beauty of Earth as seen by the Apollo astronauts in the 1960s and 1970s. (What can we see here and deduce?) Copyright © 2009 Pearson Education Canada 1-31 The Face of Earth Earth’s surface has two principal divisions • Continents • Ocean basins • Significant difference between the continents and ocean basins is their relative elevations • Why are there 2 different elevations and not just a continuous range of elevations & water depths? Copyright © 2009 Pearson Education Canada 1-32 The Face of Earth Continents • Most prominent features are linear mountain belts: folds & faults or intrusions • Shields, Precambrian crystalline rocks Ocean basins • Oceanic ridge system – the most prominent topographic feature on Earth, ~50 km wide X 2.5 km tall • Deep-ocean trenches up to 13 km deep Copyright © 2009 Pearson Education Canada 1-33 EARTH’s Topography & Bathymetry NGDC/NOAA W. Smith Copyright © 2009 Pearson Education Canada 1-34 Earth as a System Earth’s four conceptual spheres are linked as a system through their interactions Characterized by processes that • Vary on spatial scales from fractions of a millimetre to thousands of kilometres • Have time scales that range from milliseconds to billions of years • How big is ___ & How long did it take to form? Copyright © 2009 Pearson Education Canada 1-35 Earth as a System The Earth system is also powered by the Earth’s interior • Heat remaining from Earth’s formation, and heat that is continuously generated by radioactive decay, power the internal processes that produce volcanoes, earthquakes, and mountains • Volcanoes alone account for 5% of Earth’s heat loss to space • There is less radioactivity than in Precambrian Copyright © 2009 Pearson Education Canada 1-36 Earth as a System: The Rock Cycle The Rock Cycle is the loop involving the processes by which one rock type can change into another taking hours to Ga! Illustrates the various processes and paths as earth materials change both on the surface and inside the Earth Weathering to Sediments; Recrystallization to Metamorphics; Melting & Cooling to Igneous Most of the steps in the Rock Cycle happen at Plate Margins Copyright © 2009 Pearson Education Canada 1-37 Rock Cycle Somewhere rocks constantly form, change, and re-form over longs spans of time. Mountain Belts take 10’s of Ma to form Ocean Basins take ~500Ma to form & be destroyed Copyright © 2009 Pearson Education Canada 1-38 End of Chapter 1: Physical Processes Plate Tectonic Engine Geohazards Resources Scales of Observation & Global Spheres & Cycles Copyright © 2009 Pearson Education Canada 1-39