2 Continental Puzzle Do the continents fit together perfectly? What continents fit the best?What other information would you look for to provide evidence that continents may have once been part of one large continent?
3 Alfred Wegener & Continental Drift 1912 proposed supercontinentPangaeaContinents separated and drifted apart
7 FossilsMesosaurus – reptile fossils found only in southern South America and western AfricaGlossopteris – plant fossils found in South America, southern Africa, India, Australia, and Antarctica (Southern Hemisphere)
10 Rock FormationsMountain ranges of eastern South America (Brazilian Highlands) and western Africa (Cape Mountains) are the sameMountain ranges in north eastern North America (Appalachian Mts.), Greenland, Scotland and northern Europe (Caledonian Mts.) are the same
12 ClimatesGlacial evidence in South America, Antarctica, India, Australia and AfricaWhen viewed separately, glacial evidence on these continents suggests that the entire earth was covered with glaciers at one time, but this is contradicted by other evidence from sedimentary rocksWhen continents are placed together, like a puzzle, glacial evidence is not world-wide, which coincides with other evidenceTropical plant fossils in AntarcticaNo plants currently grow in Antarctica, so plant fossils found there indicate warmer temperatures at one time
15 Alfred Wegener and Continental Drift Despite the evidence that seemed to suggest Pangaea, Wegener’s continental drift hypothesis was rejected by the scientific communityIf the continents were moving apart, why wasn’t the Earth expanding?Continents don’t plow through oceanic rock, so how can they move?There was no evidence for the mechanism of tectonic plates or their movement
16 Evidence for the Theory of Plate Tectonics In the mid part of the 20th Century, discoveries were made as a result of Naval technologies that enables the mapping of the sea floorHitler had gotten very close to the U.S. in WWII, via submarines (in the coastal waters of the eastern seaboard)U.S. raced to learn more about the ocean floor in order to develop better submarine capabilities
17 Mid-Ocean Ridges and Rift Valleys 1947 mapping projectsonic technology enabled the mapping of the sea floorRift valleys and mid-ocean ridges were discoveredRift valley – a rip, or rift, in a tectonic plate at which volcanic activity is foundMid-ocean ridge – the mountain ranges found on either side of a rift valley, formed from magma building up on either side of a rift
21 PaleomagnetismMagnetometers developed during WWII to detect submarine hulls also discovered that Earth’s rock record contains magnetic reversalsNormal magnetism and reverse magnetism alternates in rocks during specific periodsMagnetic symmetry – magnetic bands (reverse and normal) are mirror images on either side of mid-ocean ridgesSuggests that magnetism of Earth changesMetals in molten magma align with the magnetism at the time of crystallizationIgneous rocks (basalt) retain the magnetic orientation at time of formation
23 Additional observations of Ocean Floors Ages of ocean floor features increase in age as distance from the ridge increasesSediments are thinner and younger nearer ridgeFossils are younger nearer ridgeRocks are younger nearer ridgeAll this suggests that new oceanic crust is forming at the rift valleys
29 Conservation of Energy According to the law of conservation of energy, energy can’t be created nor destroyed.What is the source of energy that drives volcanoes?What energy source produces earthquakes?
36 Tectonic Plates Interact The tectonic plates of Earth’s lithosphere form the pieces of a very tightly-fitting puzzle.Since plates move over the asthenosphere, they are bound to interact with each otherPlates interact at their boundaries in 3 major ways
50 Convergent plate boundary Boundary between tectonic plates that are convergingThree types of collisionsOceanic-continental collisionOceanic-oceanic collisionsContinental–continental collisions
51 Oceanic-Continental Collisions Continental crust collides with oceanic crustOceanic crust subducts – dives beneath the continental crust
52 Oceanic-Continental Collisions Common featuresSubduction zones – areas where one tectonic plate dives beneath another tectonic plateOceanic trenches – area in the ocean where oceanic plate subductsdeepest points in Earth’s oceansPeru-Chile Trench
53 Oceanic-Continental Collisions, continued Common featuresVolcanic activityMountain building – volcanic mountain ranges such as Rocky MountainsOceanic plate re-melts and rises to the surface inland from the boundary, creating mountainsEarthquakes
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