Evidence of “continental drift”—. Physical fit of continents Fossil evidence Measurements of movement Rock layer sequences Glacial evidence Key concepts 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
What evidence supports the theory of continental drift?
Shoreline Fit of the Continents
Fossil Evidence The fossils from the exact same animals are found on continents separated by vast oceans.
Matching Rock Layers
Glacier Evidence Glaciers scars are found on continents which are today too warm for glaciers.
How fast are the plates moving?
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.
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. Key concepts
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.
Mid-Atlantic Ridge = Divergent Boundary
Iceland – a continent directly over the Mid-Atlantic Ridge
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
The Himalayas Are Born…
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.
The Aleutian Islands
Forces —tension, compression shearing Key concepts 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
Most volcanoes occur at plate boundaries…
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). Real-world contexts: