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Plate Tectonics

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Plate Tectonics

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    1. Plate Tectonics The Unifying Theory of Geology

    2. The 4 “Big Ideas” in Geology The Rock Cycle (Friday’s lecture) By the mid-1700s Antiquity of Earth - “Deep Time” (Wednesday’s Lecture) By the early 1800s, millions of years Faunal Succession (Fossil Record – Core 6) By mid-1800s Plate Tectonics By late 1960s

    3. The Big Ideas ? Earth is Old and Dynamic Rather than Young and Static

    4. Recall: The Scientific Method Observations Hypothesis (a testable explanation) Includes testing by prediction More observations (testing) If ALL observations fit ---> Theory

    5. The Ancient Greeks Knew that Earth was round (not discovered by Columbus) by 300 B.C. In fact Eratosthenes (ca. 250 B.C.) measured its circumference

    6. Early Observations First European explorers started to gather knowledge on world geography Early 1500s: E.g., Magellan & da Gama

    7. Early Observations Francis Bacon (1561-1626) first noted how coasts of Africa and South America fit.

    9. The 1800s Better maps available Some people proposed that all continents could fit together In 1872, British Challenger began mapping ocean floor by soundings Similarities in rocks of NW Europe and NE America were discovered

    11. Paleontology The study of fossils

    12. Evidence from Paleontology Similar fossils in South America and Africa

    13. Glossopteris, a seed fern whose seeds are too large to be carried far by wind

    14. Mesosaurus, a fresh water reptile that couldn’t swim across the open sea

    15. Paleoclimatology

    16.

    17.

    18. in South America, Africa, India, and Australia... At same time the Northern Hemisphere had lush swamps...

    20. Coal Deposits found in Antarctica brrrrr…. Coal requires a warm, lush climate ===> What’s Antarctica like today? ===>

    21. Paleomagnetism Magnetic minerals in molten rock align with Earth’s magnetic field

    22. Paleomagnetism When igneous rock cools, magnetism is “frozen in”, like little compasses...

    23. Polar Wandering = apparent change in position of poles over time

    24. Polar Wandering Different continents indicate different position of North Pole - very strange... Only logical explanation is that the CONTINENTS have moved since the rocks were formed

    25. WEGENER and CONTINENTAL DRIFT In the 1910s Alfred Wegener put all these pieces of evidence together and made the hypothesis of CONTINENTAL DRIFT... The Origin of Continents and Oceans (1915)

    26. CONTINENTAL DRIFT When Wegener proposed to fit the continental shelves together, rather than the coastlines, we got a better fit for all modern continents...

    27. All continents have moved to their present positions from one “supercontinent” he called PANGAEA

    28. Scientific Consensus is that Earth is about 4.5 billion years old (4.5 Ga)

    29. Breakup of Pangaea

    30. 1912 - 1945 A few geologists looked for more evidence during this period... Seismologists began studying the deeper layers of the earth and discovered a dense mantle and liquid outer core.

    31. WWII and SONAR Sonar, developed to find enemy subs, was used in the decade after WWII to map the deep sea floor...

    32. SONAR Previously, most geologists thought the sea floor was rather flat and featureless They were wrong... A diverse topography was discovered

    33. Topography of the Sea Floor

    34. Topography of the Sea Floor Researchers found an undersea mountain range 40,000 miles long. And a trenches seven times deeper than the Grand Canyon. Even more striking were the geophysical findings...

    35. Some Geophysics Thousands of drilling samples were taken...

    36. Geophysics Paleomagnetism in the deep sea floor rocks indicated that many episodes of magnetic reversals had taken place...

    37. Radiometric dating showed the rocks get older the farther you get from the ridge. These reversals occur in parallel paired bands on opposite sides of a mid-ocean ridge.

    38. Sea-Floor Spreading In 1962, these data were collected into a theory called SEA-FLOOR SPREADING New crust forms at mid-ocean ridges... Oceanic crust pushes outwards from the ridge and (perhaps) takes the continents along

    39. Earthquakes and Volcanoes Seismology is the study of earthquakes

    40. Remember the Tsunami?

    41. Earthquakes and Volcanoes Data indicate that earthquakes and volcanoes do not occur at random locations, rather...

    42. Earthquakes and volcanoes occur mostly along or near trenches and mid-ocean ridges...

    43. E.g., Pacific “Ring of Fire”

    44. Seismology studies located a zone of weakness where seismic waves travel more slowly It was called the asthenosphere. The rigid lithosphere sits on top of this

    45. Finally, a unifying theory... In 1968, seismologists at Columbia put all the evidence together and came up with the theory of PLATE TECTONICS... This combined the sub-theories of CONTINENTAL DRIFT and SEA-FLOOR SPREADING

    46. PLATE TECTONICS The rigid upper 35 miles or so of the earth (lithosphere) is broken up into a dozen or so plates, which can slide around on the zone of weakness.

    64. MECHANISM Current idea: plates move as a result of mantle convection, driven by earth’s internal heat

    65. Consequences of Plate Tectonics Earthquakes Volcanoes Mountain Ranges Why it’s a “Unifying Theory”

    66. FIRST, A FEW DEFINITIONS...

    67. Types of Plate Boundaries

    68. DIVERGENT - pulling apart Mid-Atlantic Ridge Great Rift Valley of Africa

    69. Great Rift Valley of Africa

    70. CONVERGENT - coming together Japan Himalaya mountains

    71. Himalaya mountains formed when India collided with Asia

    72. TRANSFORM - slide past each other San Andreas Fault

    73. San Andreas Fault

    74. Volcanoes Are associated with divergent and convergent plate boundaries ... Why ?

    75. Pacific rim “Ring of Fire” Convergent and Divergent boundaries

    76. Earthquakes Are associated with ALL boundary types ... Why ?

    77. Mountain Building “Tectonics”

    79. Appalachians Started forming 400 million years ago (400 Ma) Cumberland Gap

    80. Rockies Started forming 60 Ma Maroon bells, CO

    81. Himalayas Started forming 30 Ma

    82. Folded Strata Rockies ? Appalachians ?

    83. MOUNTAIN BUILDING and PLATE TECTONICS

    84. CONVERGENT BOUNDARY

    85. http://www.pbs.org/wnet/savageearth/animations/rift-subduction.html http://www.cnn.com/2006/WORLD/asiapcf/11/09/new.island.ap/index.html

    86. Example: The Andes

    87. The Andes

    88. Geocycles Rocks, Water, Air

    89. GEOCYCLES Recycling of matter at or near earth’s surface Rock cycle Lithosphere Water cycle Hydrosphere Weather and Climate Atmosphere

    90. First, the ROCK CYCLE

    91. Inner core (solid) Outer core (liquid) Mantle (gooey in places) Crust (solid) 3-40 miles thick 4 concentric layers

    92. The crust, plus the upper 40 miles of the mantle, form the lithosphere, broken into plates which slowly slide around on the zone of weakness… What is the Lithosphere and what are the “Plates”?

    94. IGNEOUS RXS “Fire-formed” Liquid rock is called magma or lava, depending on amount of dissolved gas INTRUSIVE - cooled under surface Examples: Granite, Gabbro VOLCANIC - cooled at surface Examples: Basalt, Obsidian, Scoria

    95. SEDIMENTARY RX “Settling” Clastic - formed from pieces “clasts”, which come from the weathering and erosion of other rock. Examples: Shale, Sandstone, Conglomerate Bio-chemical and Organic microskeletons, e.g. in coral reefs: Limestone Salts in stagnant pools, e.g., Halite Organic - decayed remains of plants: coal

    96. METAMORPHIC RX “Changed form” Depends on original rock type and amount of heat and pressure Shale ----> Slate or Schist (more heat) Granite or “dirty” sandstone ---> Gneiss Sandstone ----> Quartzite Limestone ----> Marble

    97. IGNEOUS RXS and ABSOLUTE DATING Some igneous rocks can be radiometrically “dated” – i.e., have an ABSOLUTE AGE assigned...

    98. On the other hand… SEDIMENTARY ROCKS Are most likely to contain fossils

    99. But, SEDIMENTARY ROCKS Can only be “relatively dated”…

    100. RELATIVE DATING

    101. RELATIVE DATING

    102. DEEP TIME Oceans vs. Puddles

    103. AIR and WATER

    104. Water Facts... 70 % of Earth’s surface is covered by H2O 70 % of human body’s weight is H2O Water can exist in 3 states earth’s surface exists only as solid and vapor on Mars only vapor on Venus

    105. Mars is too cold...

    106. Venus is too hot...

    107. Earth is just right...

    108. More Water Facts... Water freezes at 0 degrees Celsius and boils at 100 degrees Celsius This is higher than similar substances because of hydrogen bonding Water is most dense at 4 oC. This explains why ice floats, which prevents lakes from freezing solid in Winter

    109. Hydrogen Bonding ........O H ........ / \ / H H ---- O | | \ O O H ......... / \ / \ H H H H ......... | | | |

    110. Water... Its heat capacity is higher than similar substances “A watched pot never boils.” Moderates Earth’s temperatures Compare San Francisco and St. Louis

    111. AIR Main gases in present atmosphere: Nitrogen (78%), Oxygen (21%), and Argon (0.9%), variable amounts of water vapor Average sea level atmospheric pressure is 14.7 pounds per square inch and decreases with altitude

    112. DISTRIBUTION of EARTH’S WATER and AIR

    113. Origin

    114. Origin How: Impact of Icy Comets and Degassing of volatiles ... bottle Earth’s atmosphere was forming 4.4 to 4.0 Ga It then (probably) consisted mainly of water vapor, carbon dioxide, ammonia, methane (Some controversy)

    115. Mt. Erebus, Antarctica

    116. Brief History Icy Comet impacts ---> add H2O to atmosphere and down to about 70km Earth cools ---> Water condenses Lots of rain; Volcanoes add CO2 Most of CO2 dissolved in oceans Photosynthesizing organisms evolve CO2 + H2O ------> C6H12O6 + O2

    117. The Water Cycle How Earth’s water and air interact ... Natural “recycling” process

    118. The Water Cycle

    119. ZONES OF CONCENTRATION Of natural waters

    120. ZONES OF CONCENTRATION Marine (saltwater)- The oceans contain over 97 % of earth’s water -- salt water Brackish (mixture of salt and fresh): Found in estuaries, where fresh and salt water meet Important to aquatic life 3rd most productive ecosystem Example: Chesapeake Bay

    122. Fresh Water Less than 3 % of earth’s water is fresh Glaciers contain over 75 % of Earth’s fresh water, but this source is not usable by biota

    124. Fresh Water Lakes and rivers contain less than 1 % Groundwater (including soil moisture) accounts for the remaining 24 % If all Earth’s water fit in a gallon jug, there would be one tablespoon of available fresh water

    125. Structure of the Atmosphere Layers classified by temperature changes ...

    126. The Atmosphere All weather occurs in the troposphere = “churning sphere”

    127. Convection causes the “churning”

    128. Convection in Humid Air

    129. Thunderhead

    130. Stratosphere The ozone layer is contained in the stratosphere ... No “churning” because of a temperature inversion, i.e., Temperature increases with altitude...

    132. The Ozone Layer Ozone, O3 , is an air pollutant in the troposphere, but in the stratosphere protects from UV radiation : O3 + UV --------> O2 + O Chlorine radicals (like from CFCs) interfere with this process: Cl + O --------> ClO

    134. Coriolis Effect Caused by an unattached atmosphere over a rotating Earth

    135. Coriolis Effect

    136. Coriolis Effect on Winds

    137. Coriolis Effect on Winds

    139. PREVAILING WINDS The direction the winds blow most of the time ... Changes temporarily due to weather systems ... In the middle latitudes (30o- 60o), the prevailing winds are from the west. These affect climate as we shall see in a moment ...

    140. PREVAILING WINDS

    141. OCEAN CURRENTS (Surface) currents caused by prevailing winds and Coriolis Effect ... They play a major role in redistributing earth’s heat ... They are called warm or cold, compared with other water at that latitude ... Example: The Gulf Stream is a warm current.

    143. Effects on Climate Many factors affect climate Prevailing winds and ocean currents are only two of these Example: Why is the weather in Paris more pleasant than in Quebec City ? Gulf Stream + Prevailing westerlies

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