1 Plate Tectonics Notes Geology – the study of the Earth and its processes

2 The Earth’s Layers Scientists study seismic (earthquake) waves and volcanic explosions to learn about the Earth’s interior. Crust Mantle Outer Core Inner Core

3  Crust –outermost layer –thinnest layer –the layer we live on –divided into pieces, called tectonic plates –two types: continental and oceanic crust  Mantle –thickest layer –“flows” and allows the tectonic plates to move on top –primarily magma The Earth’s Layers cont…

4  Outer Core –liquid  Inner Core –solid –dense, high pressure layer at the center of the earth The Earth’s Layers cont… Core is made primarily of iron and some nickel

5 Alfred Wegener proposed that all the continents were once joined as a single landmass –he called this “supercontinent” Pangaea –stated the continents have separated and collided as they have moved over millions of years –called his theory “continental drift”

Continental Drift Slide does not need to be copied 6

Wegener’s 5 major pieces of Evidence: 1. Continents (esp. South America & Africa) seem to fit together like pieces of a puzzle 2. Matching fossils occur on east coast of S. America & west coast of Africa 3. Matching folded mountain belts on coasts of S. America & Africa 7

Evidence cont… 4. Evidence of ancient climates show landmasses were once located elsewhere -Ex: glaciers in Africa ! 5. Data for latitudes & longitudes of locations is changing 8

9 Wegener is debated  Other scientists argued that the continents could not just plow through the oceans  Later evidence revealed Wegener was correct – he just didn’t have the technology to prove how the continents had moved

Modern Theory = Plate Tectonics  The crust is made up of about a dozen major, moving plates and several smaller plates  Plates can contain: –land = continental crust –ocean = oceanic crust –Both ! 10

Modern Evidence from the Oceans Scientists mapping the ocean floor found:  Underwater mountain chains  Ridges where the sea floor was actually spreading at sites called ridges  Some oceans were growing wider from the middle  Fossils and other materials are moving apart on either side of ridges  Newer, younger crust was being created by magma at the ridges 11

12  Magnetic measurements of the crust  Polarity (magnetic north vs. south) changes every so many thousand years  Magnetic rocks on the ocean floor show reversals  Rocks are in equal bands on either side of the mid-ocean ridges Modern Evidence cont…

13 What Moves the Plates?  Convection currents are created as heated rock rises to the surface, cools, and sinks again.  These currents carry the plates as if they are on a conveyor belt in conveyor belt in a process called a process called “slab pull.” “slab pull.”

14 Two different plates meet at a boundary. There are 3 types of plate boundaries: 1.Convergent = where plates collide 2.Divergent = where plates are move apart 3.Transform = where plates move up against one another

15 Convergent Boundaries:  When these 2 pieces of crust collide, they buckle and push upwards, forming mountains = uplift occurs  Ex: Himalayas & Mount Everest Type 1: continental / continental

16 continental crust to draw & label: Uplifted mountains continental crust

17  Oceanic is denser, so it sinks at the trench between the plates = called the subduction zone  The melting of the oceanic crust forms new magma which is less dense than surrounding rock, so it rises, forming volcanoes  Ex: Mt. St. Helens Type 2: continental / oceanic 17

18 continental crust to draw & label: oceanic crust trench melting volcanoes the mantle magma

19  The denser plate is subducted / sinks.  The melting of the crust forms new magma which will rise above the denser rock – as it cools, it may pile up to it may pile up to form land form land  Ex: Hawaiian Islands & Japan Islands & Japan Type 3: oceanic / oceanic

20 to draw & label: oceanic crust trench melting land & volcanoes the mantle magma oceanic crust

21 Hot Spots  In several places on earth, hot magma moves upwards through the crust  As a plate moves over this source of magma, volcanoes form at the hot spot.  As the plate continues to move, continues to move, a chain of volcanoes a chain of volcanoes of differing ages of differing ages forms forms

22 Divergent Boundaries:  The area where 2 plates are moving away from one another is called a rift zone.  Magma will rise up to fill the gap, cool, and harden to form new crust.  When this happens in the ocean, the process is called sea-floor spreading.

23 Ex: Mid-ocean ridge in the Atlantic – note: the youngest crust will be found in these areas Ex: Great Rift Valley in Africa – note: the inland sea that resulted 23

24 to draw & label: oceanic crust the mantle magma oceanic crust mid-ocean ridge sea-floor spreading

25 to draw & label: continental crust subsidence continental crust rift zone step 1 step 2 inland sea

26 Transform Boundaries:  Two plates may grind and jerk as they slide past one another.  The boundary where they meet is called a fault line.  The stressful movement often results in earthquakes.

27 Ex: San Andreas Fault Transform Boundary to draw & label:

28 continent ocean A B C D 1.Feature _____ is an ocean trench. 2.Feature _____ is undergoing subduction. 3.Feature _____ is part of the continental crust. 4.Feature _____ is part of the mantle. 5.Feature _____ is part of the oceanic crust. For discussion:

29 The “Ring of Fire” - A large number of the world’s volcanoes and earthquakes occur around the edges of the Pacific plate For discussion: