Chapter 8 Plate Tectonics
13-1 Structure of Earth (from inside to out) ______– solid, dense, hot Nickel (Ni) & Iron (Fe) o At these temperatures, Fe & Ni would normally be liquid, but the great pressure forces them to be solid. ______– hot, less dense, liquid Fe & Ni o Completely surrounds the inner core. ______– hot & plastic made of rock: Silicon (Si), Oxygen (O), Magnesium (Mg) & Iron (Fe). o Almost solid, but flows like a liquid when under pressure (like taffy or Silly Putty® ). ______– coolest, thinnest layer of Earth, varies in thickness; slowly & constantly moving & changing. o Oceanic crust more dense, basaltic & thinnest (5 km), o Continental crust less dense, granitic & thickest under mountainous regions (60 km). Science & New Ideas Alfred Wegner (Vag-ner) noticed that some continent outlines seemed to fit together like a puzzle. ______– Wegner’s idea that states continents have moved horizontally along Earth’s surface to their present positions. ______– means “all land” 225 mya, when all of Earth’s continents were joined in one supercontinent.
Evidence of Continental Drift Evidence from Fossils & Climate o Fossils of a pre-Dinosaur reptile, ______, have been found in ______& ______. o Fossils of the fern, ______, have been found in Africa, Australia, India, S. America & ______. o Fossils of warm weather plants have been found on Spitzbergen Island, in the Arctic Circle. o Evidence of Continental Glaciers has been found in S. America, Africa, India & Australia. Rock Clues o Parts of the Appalachian Mts. are similar to areas of Greenland & Europe. o Eastern S. America, Florida & western Africa have similar rock structures (Karst topography). Sea-floor Spreading Widely accepted theory proposed by Harry Hess. States that hot, less dense material in the mantle is forced upward to the surface at ______. Then it turns & flows sideways carrying the seafloor away from the ridge in opposite directions. Age Evidence found by Glomar Challenger . Found that youngest rocks (160 million years old) were at the mid-ocean ridges & got older farther away to the continents, up to 4 billion years old. Magnetic Clues at mid-ocean ridges . Earth’s ______is known to reverse itself. (______banding) . Rocks at the ocean floor showed many
magnetic reversals, proving sea-floor spreading. Theory of Plate Tectonics Plate Tectonics – a theory that states the Earth’s crust & upper mantle are broken into plates that “float” & move around on the mantle below it. o ______– Earth’s crust & upper mantle that make up the plates.
o Asthenosphere – plastic-like layer below the lithosphere, the lower mantle. (like water below a raft) o ______boundaries– areas where plates are moving apart. Sea-floor spreading in the Mid-Atlantic ridge Great Rift valley in eastern Africa.
______boundaries – areas where plates are moving together.
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______zone – area where oceanic plate sinks into the upper mantle below the continental plate. Under continental plates, create . (Alaska & west coast of U.S.) Under another oceanic plates, create deep-sea trenches, volcanoes, & volcanic islands. (Japan) . Mountain building & earthquakes happen when 2 continental plates collide. (Himalayas) o ______fault boundaries – areas where 2 plates are sliding past one another. Many earthquakes, like the San Andreas Fault in CA.
Causes of Plate Tectonics ______is a cycle of heating, rising, cooling & sinking of liquids or gases. It is thought to be the force that makes plate tectonics happen. As the Mantle is heated, it moves up to the Crust &
then moves horizontally carrying the plates with it. ______