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Chapter 4 The Restless Earth. The Composition of the Earth The Crust – outermost layer of the Earth –5 to 100 km thick –thinnest layer The Mantle - layer.

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Presentation on theme: "Chapter 4 The Restless Earth. The Composition of the Earth The Crust – outermost layer of the Earth –5 to 100 km thick –thinnest layer The Mantle - layer."— Presentation transcript:

1 Chapter 4 The Restless Earth

2 The Composition of the Earth The Crust – outermost layer of the Earth –5 to 100 km thick –thinnest layer The Mantle - layer of the Earth between the crust and the core - much thicker than the crust -contains most of the Earth’s mass

3 The Composition of the Earth The Core - layer of the Earth that extends from below the mantle to the center of the Earth - made mostly of iron

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5 The Physical Structure of the Earth Five Physical Layers -lithosphere : crust & upper rigid mantle -asthenosphere : plastic layer of mantle on which the tectonic plates move -mesosphere : strong lower part of the mantle (below asthenosphere to the outer core)

6 The Physical Structure of the Earth -outer core : liquid part of the core, below the mantle and surrounds the inner core -inner core : solid dense center of our planet

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9 Tectonic Plates lithosphere = a jigsaw puzzle tectonic plates = the pieces consist of both oceanic crust and continental crust They “float” on the asthenosphere

10 Mapping the Earth’s Interior seismic waves = vibrations produced by an earthquake -travel at different speeds depending on the density & composition of material they pass through seismographs : measure the times at which different seismic waves arrive and record the differences in their speeds * calculate the density and thickness of Earth’s layers

11 Wegener’s Continental Drift Hypothesis Continental drift : the hypothesis that states that the continents once formed a single landmass, broke up, and drifted to their present locations. Evidence fossils of plant & animal species similar rocks same ancient climate ALL found on continents that are far apart

12 Pangaea * a single huge continent * existed about 245 million years ago * split into two large continents— Laurasia and Gondwana about 180 million years ago. * ~65 million years ago split into smaller pieces

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18 Sea-Floor Spreading Mid-ocean ridges : places where sea-floor spreading takes place * magma rises toward the surface and solidifies forming new oceanic lithosphere Evidence for Sea-Floor Spreading Magnetic Reversals: when Earth’s magnetic poles change places * recorded over time in oceanic crust

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20 Mid Ocean Ridges  mid-oceanic ridge system the longest mountain range in the world  40,400 miles long like the seams of a baseball

21 Andes Mountains Run along the coast of South America Longest exposed mountain range 4,300 mi long

22 Mid-Atlantic Ridge splitting Iceland and separating the North American and Eurasian Plates.

23 East African Rift Hot spring in central rift valley, near Bogoria

24 Deepest Part of the Ocean

25 Three Tectonic Plate Boundaries Convergent Boundaries : w hen two tectonic plates collide A. continental-continental : pushes continental crust upward (mountain ranges) Subduction Zones (crust is recycled) B. continental-oceanic : denser oceanic crust gets pushed down into the asthenosphere C.oceanic-oceanic : one of the oceanic plates is subducted

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28 Divergent Boundaries : when two tectonic plates separate * mid-ocean ridges (new crust formed) Transform Boundaries : w hen two tectonic plates slide past each other horizontally *most found on the ocean floor

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30 Mid-Atlantic Ridge splitting Iceland and separating the North American and Eurasian Plates.

31 San Andres Fault The San Andreas fault zone slices through two thirds of the length of California. Along it, the Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr. Land on the west side of the fault zone (on the Pacific Plate) is moving in a northwesterly direction relative to the land on the east side of the fault zone (on the North American Plate).

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34 Possible Causes of Tectonic Plate Motion changes in density within the asthenosphere caused by thermal energy from deep within the Earth 1. Ridge-push: due to gravity the lithosphere is pulled under 2. Slab- Pull: denser oceanic crust sinks and pulls the rest of the plate with it 3. Convection: hot rock rises, then cooler rock near the surface sinks = cycle

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36 Convection Currents Convection currents in the mantle carry the plates of the lithosphere like a conveyor belt.

37 Because ocean floor is continuously created at mid-ocean spreading centers, it is far younger than most continental rock. oldest continental crust ~ 3.8 billion years old oldest oceanic crust ~ 150 million years old Spreading rate of the Atlantic Ocean: ~ 25 mm/yr

38 Tracking Tectonic Plate Motion Tectonic plate movements slow and gradual can’t see or feel them moving measured in centimeters per year (cm/yr) (GPS) global positioning system : a system of satellites used to measure the rate of tectonic plate movement

39 Convergent Boundaries Divergent Boundaries Transform Boundaries  folded mountains  tsunami  major earthquakes  trenches  most volcanic eruptions fault block mountains mid-ocean ridges new sea floor rifts weak earthquakes volcanic eruptions  moderate earthquakes

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41 Compare the mountains in the photographs. Write a description of each mountain, and suggest how it might have formed. Do you know where these various types of mountains are found in the world? Have you ever visited any of them? Would it ever be dangerous to study them? Record your responses in your science journal.

42 transform boundaries, tectonic plates, converge, divergent boundaries, diverge

43 Objectives Describe two types of stress that deform rocks. Describe three major types of folds. Explain the differences between the three major types of faults. Identify the most common types of mountains. Explain the difference between uplift and subsidence.

44 Deformation Deformation : the process by which the shape of a rock changes because of stress types of stress Compression : occurs when an object is squeezed = when two tectonic plates collide Tension : occurs when forces act to stretch an object

45 Folding bending of rock layers because of stress in the Earth’s crust  different types  can be large or small

46 Monocline fold simplest type of fold Complex Fold

47 Syncline fold Anticline fold result of compressional stress

48 Synclinal folds in bedrock, near Saint-Godard-de-Lejeune, Canada

49 Faulting a break in a rock where one rock slides relative to another Normal Faults Reverse Faults Strike-Slip Faults Animations of Faults

50 Plate Tectonics and Mountain Building Folded Mountains - form when rock layers are squeezed together and pushed upward Fault-Block Mountains - form when tension causes large blocks of the Earth’s crust to drop down relative to other blocks Volcanic Mountains – forms when rock is melted in a subduction zone = magma, which rises to the Earth’s surface and erupts

51 Other Types of Mountains Dome Mountains -formed when melted rock pushes its way up under earth Black Hills, South Dakota & Adirondack Mountains, (NY) Residual Mountains are mountains that are really plateaus that have worn down from erosion

52 Folded vs. Fault-Block Mountains

53 Great Rift Valley of Africa Tibetan Plateau

54 Folded mountains Most common type on land Appalachian Mountains (eastern North America)- old Urals (Russia)- old (200 my) Alps mountains (southern-central Europe) Himalayan mountains (southwest Asia)- young Rockies mountains (western N.A.)- young (10-25 my) Form along faults Teton Range (Wyoming) Sierra Nevada mountains = largest in the US Fault- Block mountains

55 Volcanic Mountains Andes mountains (western coast of South America) Cascade Range (runs south from British Columbia, Canada, through the U.S. states of Washington and Oregon before it becomes the Sierra Nevada mountain range in northeastern California)

56 Uplift and Subsidence Uplift: when rocks rise when a weight is removed from the crust Subsidence: when rocks sink because as they cool they become denser or when the lithosphere becomes stretched in rift zones


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