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Key concepts. Earth Composition. Crust: thinnest layer, least dense Mantle: upper most part is able to flow very slowly (asthenosphere) Core: Lower area is a solid and outer area is a liquid. Makes up 1/3 of Earth’s mass. The hottest layer with the most pressure.
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Key concepts Earth Composition Crust: thinnest layer, least denseMantle: upper most part is able to flow very slowly (asthenosphere) Core: Lower area is a solid and outer area is a liquid. Makes up 1/3 of Earth’s mass. The hottest layer with the most pressure.
Key concepts • Evidence of “continental drift”— • . • Physical fit of continents • Fossil evidence • Measurements of movement • Rock layer sequences • Glacial evidence Alfred Wegener
What is the theory of continental drift? • the idea that the continents were once all joined together in one super-continent called Pangaea and slowly moved to their current positions
Shoreline Fit of the Continents http://www.abdn.ac.uk/zoohons/lecture1/img008.GIF
Fossil Evidence The fossils from the exact same animals are found on continents separated by vast oceans.
Glacier Evidence Glaciers scars are found on continents which are today too warm for glaciers.
You may wonder… Why are the continents moving?
Seafloor Spreading The oceans are widening along the mid-ocean ridges.
Volcanoes located along ocean ridges erupt, creating new ocean floor.
Key concepts Plates—continental crust, oceanic crust Features—faults, trenches, mid-ocean ridges, folded mountains, hot spots, volcanoes Related actions —earthquakes, volcanic activity, seafloor spreading, mountain building, convection in mantle.
The earth’s lithosphere is broken into huge sections called plates that are in constant motion.
What are the plates made of? • Ocean plates are made of basalt. • Continental plates are made of granite.
Divergent Plate Boundaries Two land or ocean plates move apart in opposite directions. Magma flows to the surface between them creating new crust.
http://www.geo.lsa.umich.edu/~crlb/COURSES/270/Lec12/spreexamples.jpeghttp://www.geo.lsa.umich.edu/~crlb/COURSES/270/Lec12/spreexamples.jpeg
Subduction Zones • An ocean plate and a continental plate hit head-on. The ocean plate subducts under the continent forming a trench. The subducting plate melts. Magma rises to the surface creating a string of volcanic mountains parallel to the shoreline.
Andes Mountains Subduction zones form chains of volcanic mountains along the shoreline.
Collision Zones Two continents hit head-on, crinkling up the land into a high mountain chain.
India’s Collision with Asia Himalayas
Island Arcs Two ocean plates hit head-on. One ocean plate is forced to subduct under the other forming an ocean trench. The subducting plate melts. Magma rises to the surface forming a string of volcanic islands parallel to the trench.
Key concepts Forces—tension, compression shearing Ask a Geologist Ask an earth scientist
How does tectonic activity affect the earth’s crust? • Builds mountains • Creates deep ocean trenches • Causes earthquakes • Create volcanoes
Ocean Trenches http://www.nhusd.k12.ca.us/ALVE/wow/Ocean/seafloor.gif
http://www.thirteen.org/savageearth/hellscrust/assets/images/ringoffire.jpghttp://www.thirteen.org/savageearth/hellscrust/assets/images/ringoffire.jpg
Real-world contexts: Recent patterns of earthquake and volcanic activities; maps showing the direction of movement of major plates and associated earthquake and volcanic activity Compressional boundaries: folded mountains, thrust faults, trenches, lines of volcanoes (e.g. Pacific “ring of fire”) Tensional boundaries: mid-ocean ridges, rift valleys Shearing boundaries: lateral movement producing faults (e.g. San Andreas Fault).
