Name Layers of the Earth The earth is divided into layers based on density and state of matter. Denser, hotter layers are near the center. Crust: solid; rocky; cold; outermost layer that is broken into many pieces called plates. There are two types of crust: 1. Oceanic: dark, dense, basaltic; much thinner (in terms of depth) 2. Continental: light, lower density, granitic; much thicker, Lithosphere: the crust plus the uppermost part of the mantle Mantle: semi-solid; molten rock; warmer than crust; convection currents occur here o Asthenosphere: the upper, convecting part of the mantle Outer core: liquid (heat>pressure so it expands and melts),nickel-iron Inner core: solid (pressure>heat so it cannot expand and remains solid), nickel-iron. Nuclear reactions in the core generate heat Continental Drift The theory that the continents are in motion, first proposed by Alfred Wegener in 1912. His evidence: 1. jigsaw puzzle fit of the continents. He called the supercontinent Pangaea 2. unique fossils match across today s oceans 3. distinctive rock formations match across today s oceans Other evidence (that you will not be tested on) includes the Appalachian Mountains continuing in Northern Europe, ancient climates and paleomagnetism Wegener hypothesized that tidal forces pushed the continents through the ocean crust. But he had no acceptable explanation of HOW or WHY the continents drifted so his theory was rejected Notes: PLATE TECTONICS page 1 Draw and label the layers of the earth Draw or write something to help you remember the 3 pieces of evidence
Plate Tectonics Notes: p.2 Plate Tectonics: the formation and movement of large pieces of the earth s crust. In the 1960, new technologies such as sonar provided new data that supported Wegener s theory of moving plates. There were 5 pieces of evidence that lead to this modern theory of plate tectonics: 1. Volcano and Earthquake Patterns: Are concentrated in limited areas (thin, narrow lines) now considered to be plate boundaries 2. The Mid-Ocean Ridge is Discovered: These underwater chains of volcanoes were revealed by sonar New oceanic crust is made here There are matching bands of rocks of equal age on either side of the MOR, indicating they were made at the MOR then pushed apart 3.Magnetism As rocks cool, magnetic particles are frozen in place pointing to the N pole. So, as the plates move, the magnetic particles no longer point to the N pole. On either side of the MOR, there are alternating, mirror-image stripes of reverse magnetism (where magnetics point to the S pole!) The only way to explain this is if both sides formed at the MOR, were split apart then pusher away from each other as new lava filled in at the rift (the split). The oceanic polarity reversal and wandering N magnetic poles matches those changes on land Connect the dots and darken in the plate boundaries. How many plates do you see?
Plate Tectonics Notes: p.3 4. Heat Flow In order for the developing theory to hold true, the amount of heat in the ocean crust had to be hottest at the mid-ocean ridge where new crust is made and coldest at the trenches where old crust is destroyed (remember, as it gets older it gets colder so it shrinks and it sinks) Data collected showed the heat flow predictions were true 5. Sea Floor Elevation In order for the developing theory to hold true, the elevation of the seafloor must be highest at the hot MOR (hot=less dense)and lowest at the colder (denser) trenches Data collected showed the elevation predictions were true Remember the rhyme, as it gets older it gets colder, then it shrinks and it sinks So what Makes the Plates Move? Scientists theorize that convection currents in the mantle are the force that makes the plates split apart and move Remember that heat causes objects to expand and become less dense, so Heat Rises, Cold sinks Draw a pair of convection current using red for hot and blue for cold. Then draw the landforms associated with the rising and sinking portions Heat generated by radioactive decay in the core works its way outward, so the farther away from the core, the colder it is Plates move apart at the MOR where heat rises; plates come together at the trenches where heat sinks
Plate Tectonics Notes: p. 4 Plate Boundaries: occur where two plates meet Remember, there are two types of crust: oceanic is dark, dense, fine-grained basalt that cools quickly underwater (mafic, intrusive) and continental is light colored, less dense and granitic that cools slowly underground (felsic, intrusive) Types of Plate Boundaries Three types: Diverging, Converging, and Transform Draw the Two Types of Crust Think of words that begin with di-, meaning apart or separated 1. Diverging Plate Boundaries two plates move apart Also known as spreading centers Landforms created: long volcanic mountain chains called the mid-ocean ridges (MORs)if they occur under oceans OR rift valleys if the occur on land new oceanic crust is created here Draw and label a diverging plate boundary 2. Converging boundaries Two plates come together The type of landform depends on which type(s) of crust are on each plate 2A. Subduction Boundaries (Converging) All subduction boundaries have at least one plate with denser oceanic crust. Where the plates meet, the oceanic crust gets pushed down in to the hotter mantle, where it melts, form a deep trench parallel to the coastline. A volcanic mountain chain usually forms a short distance away. Think of words that begin with con-, meaning together or with: T Think of words that begin with sub-, meaning below or beneath
Notes: PLATE TECTONICS p.5 There are two types of subduction boundaries, based on the type of crust involved: Draw and label an oceanic-oceanic boundary i. oceanic-oceanic: two dense oceanic plates collide, forming a trench and a chain of volcanic islands called an island arc Examples: Japan, Carribean Islands ii. Oceanic-Continental: a denser, mafic oceanic plate collides with, and is pushed underneath a less dense, granitic continental plate. Again a deep trench is formed, and a volcanic mountain chain usually forms on the land Example: the Andes (S. America) Draw and label an oceanic-continental boundary
Notes: PLATE TECTONICS p. 6 2B. Collision Boundaries (Converging) Two continental plates collide. Since they are both low-density, they don t subduct. Instead, they bend and fold upwards, creating non-volcanic mountain chains Example: Himalayas, Appalachian Draw and label a Collision boundary 3. Transform Boundaries 2 plates slide past each other fault: break in crust along which movement has occurred transform faults occur at plate boundaries; on either side of the fault is a different tectonic plate (most faults are on the same plate) ex: San Andreas, most transform faults are found under the ocean, on the mid-ocean ridge; the San Andreas is one of the few seen on land Explain why the San Andreas fault occurs where it does