18Wegener’s continental drift hypothesis Alfred Wegener formed the Continental Drift Hypothesis in the 1900sContinental drift – hypothesis that the continents used to be one large mass, but have broken up to where they are now.
19support continental drift hypothesis Explain how well the continents fit togetherExplain why the same animal has fossils on opposite sides of oceansSimilar rock and climate conditions in past same on separate continents
20Breakup of pangaeaWegener named the giant land mass Pangaea which means “all earth”This would have existed about 245 million years agoPangaea split into two continents in 180 million years agoThe two land masses have been named Laurasia and GondwanaWhen laurasia and gondwana split, they formed the continents we have today
21Sea floor spreadingWegener’s hypothesis was not supported during his lifetime. People did not believe that something so big as the continents could move.It was not until many years later that scientists learned how the continents would be able to move
22Homework: read 7.2 + 7.3 for Friday! Plan! Continental driftHomework: read for Friday! Plan!
23So… What do we know about continental drift?? Who made the hypothesis?What was his hypothesis?What was his evidence for it? (4 things)
24PangaeaWegener named the giant land mass Pangaea which means “all earth”
25Breakup of PangaeaPangaea would have existed about 245 million years agoAbout 180 million years ago, Pangaea split into two continentsThe two land masses have been named Laurasia and GondwanaWhen Laurasia and Gondwana split, they formed the continents we have today
26So… What do we know about Pangaea? What was it?What does it’s name mean?How long ago was it?What did it split in to?
27OK, so how do the continents move? Wegener never lived to see his hypothesis supported, he never was able to explain why he thought the continents moved.
28Sea-Floor SpreadingThere is a chain of underwater mountains through the center of the Atlantic Ocean.This chain is just one part of a world wide system of underwater ridges.Mid-ocean ridges are underwater mountains where sea-floor spreading happens.
29Sea-floor spreadingWhen new oceanic lithosphere forms as magma rises towards the surface and solidifies.
30How does sea-floor spreading work? As tectonic plates moved apart, magma from the mid-ocean ridges fills the gapsAs the magma cools, it forms the new oceanic lithosphereOnce this new crust forms, it pushes the older crust away from the mid-ocean ridge, forcing the tectonic plates further apartThe process then repeats itself…
31Good ideas about how plates move… but do we have proof? - Magnetic Reversals
32Magnetic ReversalsThroughout Earth’s history, the north and south magnetic poles have changed places many timesWhen those poles change, the north pole has a S magnetic polarity and the south pole has a N magnetic polarityThis change is called Magnetic Reversal
33How does that prove sea-floor spreading? Any guesses?
34Proof!!The molten rock that comes to the surface at the mid-ocean ridge has tiny grains of magnetic minerals in itThe magnetic minerals are made out of iron and act like tiny compassesWhen the magma comes to the surface, the magnetic minerals align themselves with the polarity of the EarthThis means…
35This means…This means that when the magma cools and solidifies, the magnetic minerals are still aligned with the polarity of the EarthWhen the polarity switches the magnetic minerals that are in cooled magma do not change, but all the new magnetic minerals in the new magma align to the new polarityThis leaves evidence of the past polarity of the Earth
37Restless Continents Continental Drift Breakup of Pangaea Sea-Floor SpreadingMagnetic Reversal
38Finishing 7.2 and Starting 7.3 Read 7.2 and 7.3 and take notes for Friday!
39Proof!!The molten rock that comes to the surface at the mid-ocean ridge has tiny grains of magnetic minerals in itThe magnetic minerals are made out of iron and act like tiny compassesWhen the magma comes to the surface, the magnetic minerals align themselves with the polarity of the EarthThis means…
40This means…This means that when the magma cools and solidifies, the magnetic minerals are still aligned with the polarity of the EarthWhen the polarity switches the magnetic minerals that are in cooled magma do not change, but all the new magnetic minerals in the new magma align to the new polarityThis leaves evidence of the past polarity of the Earth
42Restless Continents Continental Drift Breakup of Pangaea Sea-Floor SpreadingMagnetic Reversal
43Theory of Plate Tectonics Section 7.3Theory of Plate Tectonics
44Plate TectonicsWe just learned about how the continents spread apart, but how do those tectonic plates actually move?There must be a lot of force on those plates to make them move… where does that force come from?
45Plate TectonicsThe theory that explains HOW large pieces of the Earth’s outermost crust (tectonic plates) move and change.
46Tectonic Plate Boundaries Before we can learn how the tectonic plates move, we must first learn about how the tectonic plates interact with one another.A boundary is a place where tectonic plates touch – all tectonic plates share boundaries with other tectonic plates.The type of boundary depends on how the tectonic plates move relative to one another.
47There are 3 different boundaries Convergent BoundariesDivergent BoundariesTransform Boundaries
481. Convergent Boundaries The boundary formed when 2 tectonic plates collideThere are 3 different combinations of tectonic plates that can collide1. 2 continental plates – when these collide they buckle and thicken, pushing the crust up2. continental and oceanic plates – then these collide the oceanic crust is pushed under the continental plate and into the asthenosphere, where it melts.3. 2 oceanic plates – one plate sinks under the other plate
492. Divergent BoundariesThe boundary when two tectonic plates separate or move apart from one anotherThe mid-ocean ridges that we learned about yesterday are the most common types of divergent boundariesWhen the plates move apart, sea-floor spreading happens
503. Transform BoundaryThe boundary that is formed when 2 plates move horizontally or past one anotherBecause tectonic plates have rough edges, they rub against one another causing earthquakesThe San Andreas Fault in CA is a good example of a transform boundaryThat is where the Pacific plate and the North American plate meet
51Read 7.2 and 7.3 and take notes for Friday! Finishing 7.3Read 7.2 and 7.3 and take notes for Friday!
52What do we know so far?Plate tectonics is a theory. Lithosphere holds tectonic plates, they move on the asthenospherePlate boundaries – there are 3 different ways tectonic plates can meet1. Convergent boundaries2. Divergent boundaries3. Transform boundaries
53Why do tectonic plates move? One idea: the solid rock of the asthenosphere moves very slowlyThe density of parts of the asthenosphere changes as they get heated from the rock below. The hotter rocks expand, and therefore become less dense. This causes them to move closer to the surface.Once they cool, they shrink and become more dense. This causes them to sink down again.Since tectonic plates rest on the asthenosphere, they move when it moves.
54Why do tectonic plates move? Another idea: the lithosphere near mid-ocean ridges pushes the lithosphereThe mid-ocean ridge is higher than the place where the tectonic plate sinks down into the asthenosphere. Since it is higher, the lithosphere slides down from the ridge to the asthenosphere due to gravity.Since tectonic plates are on the lithosphere, they move.
55Why do tectonic plates move? Another idea: when the lithosphere sinks into the asthenosphere, the lithosphere layer is much more dense than the asthenosphere.Just like the other idea, the denser rock is pulled down to the bottom of the asthenosphere. Therefore, the tectonic plate gets pulled deep into the asthenosphere, and starts to pull the rest of the tectonic plate down too.
56How fast can tectonic plates move? The speed depends on how large the tectonic plate is and how it is interacting with the tectonic plates around it.However, scientists are able to track tectonic plate movements and, on average, they move only centimeters a year.We cannot see this change since it is so slow.
57So how can we measure the speed? Scientists have GPS systems up in spaceThese systems monitor how far away certain ground stations are from the GPS.Scientists are able to see that the ground stations are changing their distance from the GPS. They are able to calculate how fast that is happening over a long period of time, giving us an idea of how fast the plates are moving.
58Plate tectonics?The theory that the lithosphere is divided into tectonic plates that move slowly across the asthenosphere
59How fast do tectonic plates move? A few centimeters per year
60What are the 3 ideas about how tectonic plates move? 1. Mid-ocean ridges pushing the lithosphere down into the asthenosphere because of gravity (ridge push)2. The asthenosphere changing density and moving due to changes in heat (convection)3. Oceanic plate being pulled down into the asthenosphere because it is denser (slab pull)
61How do we use GPS to track tectonic plate movement? It records the distance between the satellite and ground stations. Over time, it calculates the change in the distance.
62Current review of chapter 7 Take out reading notes from 7.2 and 7.3
63Earth PosterUse as many vocab words as possible to make huge review poster of what we have learned so farWe can make it on the board and you can take a picture of it, or you can make it individually
67Deforming the Earth’s crust Take the popsicle sticks. Slowly and carefully bend it. What happens?Now take a popsicle stick, bend it quickly and further. Now was happens?Why do they behave differently?The amount of stress you put on the stick changes. This same thing happens to rocks, the behaviour changes based on how much stress is put on them
68DeformationDeformation is what happens to the shape of the rock because of stressJust like the popsicle sticks, rocks can bend or break depending on how much stress is put on the rock
69CompressionThe stress that occurs when forces act to squeeze the object. When this happens to convergent boundaries, mountains can form.
70TensionThe stress that occurs when forces act to stretch an object. This generally happens at divergent boundaries when plates pull away from one another.
71Folding When stresses act on rocks, they cause the rocks to fold. The bending of rock layers is called folding.Rocks generally start as horizontal layers, like the three examples, so when we see that they are bent, we know deformation happened.
72Do paper experiment Take at least 5 pieces of paper Put water on the paper so it is dampUse your hands to put horizontal stress on the paper
73Direction of stressWhen horizontal stress in put on the rocks, you tend to see upward-arching folds and downward-arching folds. Do you see any of this with your paper?When you have vertical stress on the rocks, the rocks shift, but both sides of the rock are still horizontal. Look at the example on the desk, when you put horizontal stress on the rocks, only the middle section changes.
75Force on Rocks Fold the paper in front of you in half Continue the processCount how many times you can fold it in halfDoes it get more difficult to fold? Why?With every fold, the amount of paper doubles. After 7 folds there are 128 sheets. The Earth’s crust, like the paper, requires a small amount of pressure to fold the lighter, thin layers. Tremendous amounts of pressure are required to fold over large, denser sections of land.
76FaultingSome rocks break when stress is applied to them. The surface the rocks break along is called a fault. The blocks of crust on either side of the fault are called fault blocksWhen the fault is formed, the fault is normally not perfectly vertical, there are 2 different shapes of the fault blocks.Hanging wall and footwall
77FaultA break in a body of rock along which one block slides relative to another
78Fault Blocks Look at the blocks in the front of the room Which one looks like a footwall?You can use your feet to walk up a footwallWhich one looks like a hanging wall?You would rock climb off of the hanging wall
79Types of FaultsThe type of fault that forms is determined by how the two fault blocks relate to one another
80Types of Faults Normal Fault Reverse Fault The hanging wall moves down Normally occurs when the tectonic plates pull rocks apart - tensionReverse FaultThe hanging wall moves upNormally occurs when the tectonic plates push rocks together - compression
81Telling the difference You can draw arrows on the picture of the fault blocks to tell which type of faults were formedYou look at the layers of rocks and see which way the hanging rock has moved
82Strike-Slip Fault This is another type of fault This forms when forces cause the rock to break and move horizontally across each other. You do not have footwalls and hanging wallsThese faults do not cause the rocks to move up and down, they cause the rocks to move left and right
84Types of mountains Folded Mountains Fault-Block Mountains Highest types of mountainsFormed when rocks are squeezed together are pushed upwardsEx. Appalachian mountainsFault-Block MountainsTension causes large normal faults to formProduced sharp, jagged mountainsEx. Tetons mountains
85Types of Mountains Volcanic Mountains Most happen at convergent boundariesForms when magma rises to the Earth’s surface and erupts
86Uplift When parts of the Earth’s crust moves up – to higher elevation Forming mountains is an example of upliftCan happen when a weight is moved from the crust, and previously depressed rock is now uplifted back to the original position
87SubsidenceWhen parts of the Earth’s crust is moved down – to lower elevationWhen rocks cool, they take up less area and subsides to lower elevations.Ex. When the lithosphere coolsThis can also happen when the lithosphere is stretched from being on a rift zone. A rift zone is the area between two tectonic plates, when the plates move away, the rock in between the plates sinks.
88Any questions?This is the last part of the chapter, we are having our test on Thursday, does anyone have any questions right now that they are confused about?
89Do Stretch Lab In groups, take a balloon. Draw 3 touching columns on your deflated balloonColour in the 2 outside columnsInflate the balloon, what happens to the drawing?Deflate the balloon, what happens to the drawing?
90Make an OutlineLet’s make an outline of all that we need to know for this testWhat vocab words do we need to know?What concepts do we need to know?What would be a good way to remember them?
92Review Time – pagesWhat I want you to do this period is either make a poster or a few posters of all of the vocab words and main ideas, OR make flashcards about the vocab words and main ideas!This will help you learn and understand the material better, you will also be able to use what you make for studying.Also, organize your notes, let me look them over.If you come across anything you do not understand, ASK ME!