Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Where did the idea come from that the continents were once connected? • As long ago as 1620, the English thinker Francis Bacon noticed similarities between the coasts of South America and Africa. What is continental drift? • Continents were once connected into one supercontinent and have since drifted to their current positions • Alfred Wegner developed the idea in 1912 – He called the supercontinent Pangaea all gaea = ________) land PANGAEA (greek: pan = _____, • Stretched from pole to pole • Centered where Africa is today Wegner’s Evidence Supporting Continental Drift • Coastlines • Landforms • Fossils • Climate Continental Drift Evidence Coastlines • Coasts of some continents look like they fit together. Example: east coast of South America and west coast of Africa Continental Drift Evidence Landforms • Mountain ranges on different continents line up • Similar coal and rock formations found on different continents line up; are same age Example: Appalachians line up with the mountain ranges in Europe. They are the same type of rock and age. Continental Drift Evidence Fossils • Fossils of the same organisms are found on different continents Continental Drift Evidence Climate 1. Evidence of past tropical climates in the Antarctic Example: fossils of Glossopteris (tropical plant) found in areas that are now colder Continental Drift Evidence Climate 1. Evidence of past tropical climates in what is now the Antarctic 2. Evidence of glacier marks in what is now the tropics Continental Drift Why was the idea of continental drift rejected for more than 40 years? Wegner could not provide the force that caused the continents to move. How could huge solid chunks of land have plowed through the ocean floor??? What Is the Theory of Plate Tectonics? • Pieces of Earth’s lithosphere are in constant slow motion; driven by convection currents in the asthenosphere • Explains creation, movement, destruction of Earth’s plates What Are Plates and Plate Boundaries? • Plates: broken pieces of the lithosphere • Plate boundaries: the edges of the plates What Happens at Plate Boundaries? • Plates can pull away from each other –Divergent boundaries • Plates can grind past each other –Transform boundaries • Plates can crash into each other –Convergent boundaries Divergent Plate Boundary • A place where two plates move apart or divide • Crust is created from cooled magma What geologic features form at divergent plate boundaries? 1. Mid-ocean ridges – divergent plate boundaries beneath the ocean – world’s longest mountain range! – circle Earth like a seam on a baseball – Example: Mid-Atlantic Ridge Volcanoes http://www.smithsonianmag.com/specialsections/lifelists/Icelands-Volcanoes.html# Eldfell in Heimaey What geologic features form at divergent plate boundaries? 2. Rift valleys – divergent plate boundaries on land – Examples: Rio Grande Rift (North America), Great Rift Valley (East Africa) http://worldwildlife.org/photos/great-rift-valley-kenya http://www.getintravel.com/great-rift-valley-kenya/lanscape-of-the-great-rift-valley-in-kenya-africa/ Transform Plate Boundary • A place where two plates grind past each other, moving in horizontal opposite directions • Crust is neither created nor destroyed http://geology1403.blogspot.com/2011_09_01_archive.html What geologic features form at transform plate boundaries? • Responsible for creating strike-slip faults, which lead to strong earthquakes – Example: San Andreas Fault (Calif.) San Andreas Fault Convergent Plate Boundary • A place where two plates come together • Crust is destroyed due to subduction (edge of plate sinks under another plate into the mantle) • Collisions happen between: 1. Oceanic/Continental 2. Oceanic/Oceanic 3. Continental/Continental What geologic features form at convergent plate boundaries? 1. Collision between oceanic crust and continental crust – basalt (oceanic crust) more dense than granite (continental crust) – forms deep ocean trenches where ocean crust is subducted into mantle – forms volcanoes on continent due to melting crust – Examples: Andes, Cascades, Sierra Nevada DEEP-OCEAN TRENCH Link to Simulation Subduction & Volcanic eruption What geologic features form at convergent plate boundaries? 2. Collision between oceanic crust and oceanic crust – forms deep ocean trenches where one ocean crust is subducted under the other – forms volcanic arc islands – Examples: Aleutian, Tonga, Mariana Islands Link to Simulation What geologic features form at convergent plate boundaries? 3. Collision between continental crust and continental crust – forms high mountain ranges – Examples: Himalayas Link to Simulation Collision of India and Asia