Chapter 3 Earth Structure and Plate Tectonics

◦ The inner core is primarily iron and nickel plus other heavy elements. It is theorized to be solid due to enormous pressure. ◦ The outer core is made up of the same elements. T his layer is liquid and its movement is thought to produce earth’s magnetic field.

◦ The mantle is thought to contain mostly silicon and oxygen, with some iron and magnesium. Solid/liquid mixture that moves in convection circles. ◦ The crust is composed mainly of oxygen, silicon, magnesium, and iron. Two types of crust: continental and oceanic. Solid.

 Oceanic Crust  Denser, thinner and younger than continental crust  Oceanic crust lies lower on the mantle because of increased density.  Continental Crust  Lighter, thicker and older than oceanic crust  Continental crust rises higher above mantle because of lesser density.

 Color  Include all labels  Use the text to describe each of the layers: lithosphere, asthenosphere, lower mantle, core  Use the text to explain how oceanic and continental crust are different. Lithosphere - _____________ Asthenosphere - __________ Lower mantle -____________ Core – ____________________ Oceanic vs Continental crust ___________________________

 Sir Francis Bacon (1600s)and Leonardo DaVinci(1500s)  Noticed that the continents seemed to fit together like a puzzle  Alfred Wegener backed up idea with evidence:  Coal deposits and other geological formations across oceans matched  Fossils of a land reptile across oceans also matched  Fossilized tropical plants in Antarctica

 States that continents were once joined to form Pangaea over 200 million years ago.  Broke up into pieces and continents float on top of a liquid mantle and are constantly drifting.  Volcanic activity was powered by continental movement.  He incorrectly thought the continents moved because of the rotation of the Earth.  Most detractors did not believe that the continents could float on top of a liquid mantle.

 Crust is broken up into lithospheric plates that move on top of the mantle.  The plates move because of convection currents in the mantle.

Plate Tectonics Map by USGS

 Zone along the edge of the Pacific Ocean that has many volcanoes and earthquakes.  This horseshoe-shaped belt stretches about 25,000 miles.

 Place where crust moves over a mantle plume (column of superheated mantle).  Magma seeps out, cools, and hardens: forms an underwater volcano  Magma continues to build up until it breaks the surface of the water forming an island  Significant because hot spots do not move with tectonic plates because they originate in the mantle.  Volcanic island chains, are the result of the plate moving over a hot spot.

◦ 1. Orderly pattern of oceanic ridges and volcanoes suggesting the Earth’s crust is divided into sections. ◦ 2. Sediment samples – the layers were thin or absent at the oceanic ridges, and thicker away from the oceanic ridges. This suggests newer crust at the ridges. ◦ 3. Radiometric dating was used to determine the age of rocks. Scientists have found seafloor rock to be significantly younger than rock in the center of the continents. ◦ 4. Magnetometer data -This instrument measures the polar orientation of magnetism of minerals. A symmetrical pattern exists in the magnetic alignment in seafloor rock. This pattern radiates outward from the point of seafloor spreading.

Age of Oceanic Rocks: Red = NewestBlue = Oldest

 At a spreading or divergent boundary, two plates are moving apart. As this happens, the crust pulls apart and forms valleys. Magma flows up through the rift valleys creating new crust and widening the seafloor.  At a colliding or convergent boundary, two plates push together. ◦ They are also called destructive boundaries because movements along these destroy crust.  At a transform boundary or fault, two plates slide past each other.

Divergent Boundary Mid-ocean ridges and rift valleys mark divergent boundaries.  Cause seafloor spreading  Volcanoes along oceanic ridges  Only one island above water: Iceland

 Because it is on a spreading zone, magma is very near to the surface  This produces hot springs ◦ Pools of warm water at the surface ◦ Temperatures can be 150°F and more (very warm bath water)

 Oceanic-Oceanic  Causes underwater volcanoes and island formation.  Continental- Continental  collide and “push together” forming mountain chains ◦ Example: Himalayas

 Continental- Oceanic  The oceanic plate is subducted underneath the continental plate  As plate moves down into mantle it melts  Increased magma is forced up through surface forming land volcanoes ◦ Example: Mount St. Helens

 Also called transform faults or shear boundaries  Plates move side-by-side, but in opposite directions  No sea floor is created or destroyed  Earthquake activity due to friction ◦ Example: San Andreas Fault in California

 Use the descriptions in table 3.1 pg 75 to draw all the types of plate boundaries.  Divergent Boundaries ◦ Ocean-Ocean ◦ Continent-Continent  Convergent Boundaries  Ocean-Ocean  Continent-Continent  Ocean-Continent  Transform Boundaries  Illustrations must be colorful, fill the entire poster, show direction of plate movement, label type of boundary, and describe events observed there.