UNIT 10 Plate Tectonics Study Guide
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UNIT 10 Plate Tectonics Study Guide Chapters 1, 2, 9, and most of book (Revised 7/18) UNIT 10 HOMEWORK worth 10 points VIDEO WEB HIT HOMEWORK: Write two paragraphs with minimum of three sentences each (PHYSICAL GEOLOGY 1303) (Revised 7//18) UNIT 10 Video Hits For Unit 10 Video Hit, go to the “DMC HOME” website; in Search box –type “Kramer”, select “Faculty Listing”; click on Walter Vernon Kramer, click on Website“, scroll down and click GEOL 1303; then select “Video Hit Link Number 10”, and click on icon, watch video of life forms that don’t need sunlight!. [IF NONE OF THE WEB SITES COME UP, YOUR COMPUTER PROBABLY NEEDS TO BE REBOOTED (RESTARTED) General -Tectonics: the branch of geology that studies regional and global structural features on Earth -Plate tectonics: the unifying theory of global dynamics. The lithosphere is believed to be broken into individual plates that move in response to convection within the Earth’s upper mantle. -Plate tectonics theory explains the interrelationships of volcanoes, earthquakes, climate, mountains, and even evolution. Historical Studies of the Ocean Floor -Evidence for tall mountains under the Mid-Atlantic Ocean was presented in the 1850s. -The laying of the transatlantic telegraph cable 1860s proved that there was a mountain range in the middle of the Atlantic Ocean. 1850 map 1908 map FYI In 1878, Wyville Thompson compiled ocean depth data from the scientific sailing ship (the HMS Challenger) and collected samples of rock (basalt) from these deep-underwater mountains. Thirty years later in 1908, this data was compiled and the results further implied an extensive mid-Atlantic mountain range (which was largely ignored). By the 1940s several” lines” of sonar mapping across the Atlantic Basin further demonstrated that the (underwater) mid-oceanic mountain range was very extensive. Continental Drift Theory Introduction -Alfred Wegener was a German scientist (geologist) who authored a book in which he carefully and systematically presented evidence for continental drift (1915). -Continental drift: A theory proposed by Alfred Wegener, in which he tried to demonstrate that the Earth’s continents actually “move” in relation to one another. -Pangaea: (in Wegener’s theory of continental drift) The last ancient super-continent that included all of the today’s major continental land masses. 1 Wegener’s Evidence for Pangaea - Similarities in shorelines (or continental edges) of Africa and South America are very noticeable. - There is a puzzle-like fit of the continents of Africa and South America as well as that with other continental land masses. -Distinctive, matching rock formations can be found in America, Europe, Africa and South America. - If realigned, the Appalachians and European Caledonian Mountains would form a single mountain chain of similar aged rocks. - We can readily match rock types that have ages of 2 Billion Years to 0.5 Billion Years along the Africa - South America continents, but cannot match rock types younger than 145 million years. - A massive ancient continental glacier must have covered several of these continents at the same time. This could be demonstrated by studying the ancient glacial striations remaining from that glacier. - Paleo-climatic studies of coral reefs such as El Capitan Mt. in West Texas imply that certain portions of today’s continents are previously located near the Equator. Ancient sand dunes in rock strata on many continents imply single massive continental desert belts in the past. Nothing will ever be attempted if all possible objections must first be overcome – Samuel Jackson 2 -Distinctive, matching species of fossil plants, amphibian fossils and reptile fossils found in Africa, South America, India, Australia and Antarctica imply a single continent because of very low biodiversity of the various species. - Biodiversity Similar plant and animal species within one large ecosystem will become rapidly become dissimilar from previously identical species when their ecosystem becomes isolated ecosystem from the large system. (This is true especially if those ecosystems are separated by land masses or oceans. For example only those monkey species from South America have prehensile tails as compared to those monkey species found in the rest of the world.) - Similarities of plant fossils and reptile fossils suggested a continuous landmass before 145 million years but afterwards there is a noticeable difference between “similar” fossil species. - Coal and reptile fossils in Antarctica imply that this land mass had been warm at one time. Thus Antarctica had been “drifting” from an area of warm climates to its current position. - “Continental drift” theory was rejected because there was no acceptable method to move the continents. If you state that continents move, you must present an acceptable mechanism that can “move” these continents over the globe! FYI: Geophysics in the early 1900s had already established that the Earth’s sphere consisted of a crust, mantle, outer liquid iron core and a solid iron core. In 1929, A. Holmes declared that the Earth’s mantle had convection cells that could move the Earth’s crust (ignored by most scientists). Knowing is not enough, we must apply that knowledge Willing is not enough, we must do. – Wolfgang von Goethe 3 Earth’s Physical Interior (Review from Unit 1): 1) The word lithosphere means a rocky sphere. Earth’s lithosphere is the solid, strong and somewhat rigid outer layer that includes the both the oceanic crustal rocks and the continental crustal rocks with a thin layer of mantle rock material this is “frozen” onto both of the (upper) visible crusts. 2) The asthenosphere represents a plastic-like zone of partially-melted upper mantle rocks. 3) The Mesosphere Lower Mantle is that rocky zone between the asthenosphere and the liquid outer iron core. Earth’s internal heat (largely generated by radioactive decay) is transferred from the core, through the mantle, to the asthenosphere. 4) We have a core that has 2 components: a) Liquid outer iron core: (FYI: 1300 mi) a mass of liquid iron (with minor amounts of other metals and rocks) b) Solid iron core (FYI: 720 mi. thickness) There are lots of theories as to the exact chemical composition of Earth’s solid iron core. Drawing of Earth’s interior Earth’s Magnetic Shield - The rotation rate of Earth’s interior solid iron core spins faster than Earth’s liquid iron core. - The solid iron core has been found to spin at a rate [2/3 second] faster than the rest of the planet while the liquid iron core spins opposite of Earth’s rotation. This spin difference generates a magnetic field or magnetic shield that encompasses the Earth. - Earth’s magnetic field creates a Magnetic North Pole (over Canada) and a Magnetic South Pole that we all can easily detect with a compass. - It is the magnetic shield (and the ozone layer) that protects life on Earth from the effect of deadly radiation and cosmic rays that is generated by our sun and other stars. Without these shields, most life on Earth would disappear within a year. - Visible evidence of Earth’s magnetic shield is with the Northern Lights or the Aurora Borealis. Green light is from oxygen 70 – 100 miles up, lower red light is from oxygen 50 to 70 miles up A wise person makes more opportunities than he finds – Frances Bacon 4 Earth’s Magnetic shield Magnetic Poles - The “exact Magnetic North Pole” location wanders within a small area near the True North Pole. - Averaged over time, the Magnetic North Pole can be considered to be at the same location as the True North Pole (axis of rotation). Magnetism and Magnetite -. Magnetite: an iron oxide mineral that can maintain a magnetic field as it forms. - Most magnetite grains found within cooling basalt magmas can “align” themselves to the north and south magnetic poles that is present at the time of the grain formation. - Magnetite grains in some types of sandstone and in oceanic sediments can also “align” themselves to the north as the grains are settling during deposition. -FYI Most animals that migrate long distances have been shown to have tiny magnetite grains within their brain (missing in most human males – ha ha). Thus most animal migration routes follow Earth’s “magnetic field lines”. Using Magnetic Fields to Study Geology - Paleomagnetism is the study of ancient magnetic fields, as preserved in the magnetic properties of certain rocks that contain magnetite. - A magnetometer is an instrument used to measure magnetic fields. - The paleomagnetic study of basalts on several continents gives supporting evidence that today’s continents have moved over time to different global positions than they now occupy. Paleomagnetic studies 5 Some Magnetic Properties - Magnetic reversal is a complete 180 degree reversal of the polarity of Earth’s magnetic field (North becomes South and visa versa). These are caused by the iron core spinning in opposite directions. - Magnetic reversals may occur at any time. For example, these reversals have occurred more than 171 times on the Earth during the last 76 million years. - Intervals of shorter magnetic reversals are termed polarity events. - Geomagnetic time scale represents a time scale that relates these patterns of magnetic reversals to the various geologic ages of the Earth. - Sunspots are “cool dark spots” on the sun that represent concentrated magnetic fields. - These spots on our Sun show reverse polarity (N-S) (or magnetic reversals) at 11 year cycles. Descriptions of the Seafloor - The seafloor was mapped in detail by many nations during the 1960s because of national security concerns. Most used using sonar (underwater sound waves) and magnetometer instruments to bring out the detail of the Earth’s ocean floors. Mountains on sea floor - These massive seafloor surveys discovered: 1) The sea floor is divided by a large ridge (mountain) system that extends almost 40,000 miles in length and is about 900 miles wide.