1st Edition NR 150 Lecture 4 Outline of Last Lecture I The Age of Discovery II Earth and the Ocean III The Young Earth Outline of Current Lecture IV Continental Drif V Earth s Structure 2 approaches to viewing the structure VI New Technology leads to the explanation of Continental Drif Theory Current Lecture I Continental Drif a Charles Darwin realized that a balance exists between the tectonic forces that uplif the Andes Mountains and the weathering forces that slowly erode the mountains down b Alfred Wegener i Proposed the theory of continental drif in 1912 ii Realized that all of the continents would fit together into one giant landmass which he called Pangea 1 The mountains of Eurasia and North America lined up 2 Fossils of animals and plants found at one part of the world could also be found in other parts of the world iii Explained his theory by attributing movement to centrifugal forces and inertia tidal drag from the Sun and Moon 1 This explanation is incorrect and was later disproved iv He attempted to conduct an expedition to Greenland in 1930 to prove his theory but he died before the trips completion v Support for Continental Drif These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute 1 Puzzle pieces fit together 2 Evidence of similar fossils 3 The lining up of mountain ranges vi Problems with Continental Drif 1 There was no mechanism that Wegener could come with to explain the phenomenon c Theory of Plate Tectonics i Progress was made in understanding that the Earth was density stratified and that the interior of the Earth is hot ii Progress with the Theory of Plate Tectonics came from the study of seismic waves earthquakes 1 Seismographs instruments that measure and record seismic activity and earthquakes 2 Seismic waves proved Earth s interior structure 3 Surface waves a Move along the Earth s surface most destructive to property b Travel slowly along the surface and have long wavelength c The greater the amplitude of the waves the greater the damage 4 Body Waves a P Waves compressional waves that changes the volume of rocks compressed or expanded i Can pass through solids liquids and gasses ii They are the 1st waves recorded by seismographs iii Travel quickly at about 6 km s b S Waves shear waves move perpendicular to the direction of wave travel i Can only pass through solids not liquids and gasses ii Travel slower than P Waves at 3 5 km s and are recorded later by seismographs iii The measurement of seismic waves proved that the Earth was layered 1 If the Earth was homogeneous the seismic waves would radiate from the site of an earthquake through the Earth in straight lines 2 P Waves can penetrate the liquid outer core but are bent as they move resulting in shadow zones where seismic activity from an earthquake isn t detected 3 S Waves cannot travel through the liquid outer core so their shadow zone is much larger than that of P Waves II Earth s Structure 2 approaches to viewing the structure a Chemical Composition i Looks at the chemical composition of the Earth ii Results from the accretion process of the young earth and subsequent density stratification iii Chemical characteristics of Earth each layer is composed of different materials 1 Crust uppermost layer thinnest layer a Oceanic crust comprised of basalt b Continental crust comprised of granite less dense than basalt 2 Mantle the layer beneath the crust a Accounts for 68 of the Earth s mass and 3 of its volume b Consists mainly of silicon and oxygen with some oxygen and magnesium 3 Core inner and outer core a Mainly consists of iron and nickel b Physical composition i Different materials behave differently with depth properties are affected by temperature pressure and depth ii Earth s interior layers are in a state of isostatic equilibrium the balanced support of lighter material in a heavier supporting matrix iii Lithosphere 1 The cool rigid outer layer about 100 200 km thick 2 Comprised of the continental and oceanic crusts and the uppermost cool and rigid portion of the mantle iv Asthenosphere 1 The hot partially melted slowly flowing layer of the upper mantle below the lithosphere 2 Extends to a depth of about 350 650 km v Lower Mantle 1 Extends to the Earth s core 2 Similar in chemical composition to the asthenosphere the upper mantle 3 Hotter than the asthenosphere but not melted due to higher pressure at greater depths a Denser material that flows more slowly vi Core 1 Extremely hot temperatures and high pressure 2 Outer core dense viscous slow flowing liquid 3 Inner core solid densest material on Earth III New Technology leads to the explanation of Continental Drif Theory a Wegener s theory was discarded until new technology came out that was able to prove his hypothesis i Seismographs revealed a pattern of volcanoes and earthquakes ii Radiometric dating of rocks revealed a surprisingly young oceanic crust iii Echo sounders revealed the shape of the Mid Atlantic Ridge b Convection i Movement within a fluid resulting from differential heating and cooling of a liquid hot material rises as cool material falls ii Provided the mechanism used to prove plate tectonics theory c Seafloor spreading i Powered by convection currents in the mantle ii Mid Ocean ridges were the spreading centers iii Source of new ocean floor rising from the asthenosphere iv Hot near the ridges due to the rise of lava to create new crust but as the crust distanced from the ridge the material became denser and the ocean became deeper v The earth isn t constantly expanding because the spreading is counteracted by subduction zones where oceanic crust is circulated back into the mantle d In 1965 the idea of Continental Drif and Seafloor spreading became better known as the concept of Plate Tectonics i The theory was mainly worked on by John Tuzo Wilson at University of Toronto