Plate Tectonics

Earth’s Interior A. The Composition and Structure of the Earth Most information scientist have gathered about the interior of the Earth come from instruments, rock samples and earthquake data. The Earth is divided into three layers: crust, mantle and core.

Earth’s Interior cont. The Crust a. The outermost layer of the Earth./ Lithosphere [land layer or rock sphere] divided into tectonic plates. b. Ranging from 5 to 100km thick (actually the thinnest layer of the Earth). c. Layer we live on.

Earth’s Interior cont. d. Two types of crust 1. Continental crust (composition similar to granite) *Oxygen, sodium, Potassium, aluminum, & silicon *Average thickness of 30km (5 to 100km) 2. Oceanic Crust – (composition similar to basalt) * iron, magnesium, and calcium * Average thickness of between 5 to 8km * Denser than continental crust

                                                                                                                                                                                  

Earth’s Interior cont. 2. The Mantle a. The layer of the Earth between the crust and the core. b. Contains most of the Earth’s mass. c. Composition: iron & magnesium d. Moho is the boundary between the crust and the mantle. *Plasticity – when a solid has the ability to flow. (the higher temperatures in the mantle allow the solid rock to flow and change shape.

Earth’s Interior cont. 3. The Core a. Inner most layer of the Earth.                                                              3. The Core a. Inner most layer of the Earth. b. Mostly made of iron, (may explain the magnetic field that surrounds the Earth.) nickel and possibly sulfur and oxygen. c. Made of two parts 1. Inner Core – solid, inner most layer. *temperature reaches 5000C

Earth’s Interior cont. 2. Outer Core- surrounds the inner core. * molten/ liquid * temperature range 2000 C to 5000 C The speed of seismic waves (earthquake waves) help to determine the density and thickness of the Earth’s layers. The third layer of the earth is underneath the mantle, known as the liquid outer core. At about 1,300 miles thick, it is almost entirely made of iron, nickel, and oxygen. The heat is so intense that the metals are molten, and the layer flows very slowly, generating energy that produces the magnetic field of the earth.

Earth’s Interior cont. B. Tectonic Plates Tectonic Plates are pieces of the lithosphere that move on top of the mantle. (Pieces of a puzzle) 10 Major Tectonic Plates Pacific Plate North American Plate Cocos Plate Nazca Plate South American Plate African Plate Eurasian Plate Indian Plate Australian Plate Antarctic Plate

Restless Continents Earth’s Changing Surface: Evidence of Crust Movement 1. Distorted Layers 2. Sedimentary rocks in high places. 3. Fossils 4. Thick rock layers 5. Geosynclines: shallow basin where the Earth’s crust sinks as sediments build up.

Restless Continents cont. B. Earth’s Drifting Continents 1. Pangaea – “all Earth” the Earth believed to be one giant land mass that broke up into large pieces, which have drifted apart. 2. Theory of Continental Drift – theory of Pangaea * proposed by Alfred Wegener (early 1900’s)

Restless Continents cont. 3. Evidence a. Fossils – fossils of the same plant and animal species found on both sides of the Atlantic Ocean b. Rocks – glacial deposits c. Continental Boundaries form somewhat of a puzzle. C. Sea- Floor Spreading * New evidence for drift 1. Sea-floor spreading is the process where new oceanic lithosphere is created as older material is pulled away.

Sea-Floor Spreading

Restless Continents cont. 2. As tectonic plates move away from each other the sea floor spreads, and magma fills the gap. 3. Mid-ocean ridge – places where sea-floor spreading takes place. (underwater mountain chains that run through the Earth’s ocean basins, ex. Mid-Atlantic Ridge) 4. Older crust is farthest from mid-ocean ridge closest to continents. A vast chain of mountains that runs along the centers of Earth's oceans

Restless Continents cont. 5. Evidence of sea-floor spreading is Magnetic Reversals a. when the Earth’s magnetic poles change place. b. reversals recorded in the ocean floor – molten rock at the mid-ocean ridged contain tiny grains of magnetic minerals, these minerals act like compasses. They align with the magnetic field of the Earth, creating a band of stone recording the ocean. When the Earth’s magnetic field reverses, a new band of stone is started. This time the magnetic mineral grains point in the opposite direction. Magnetic Reversals: Magnetic reversals usually occur a few times every million years, but when superplumes activity occurs magnetic reversals stop for the millions of years they are active. Notice the below left chart: During the Cretaceous no magnetic reversals occured. This is some of the evidence that superplumes are active. The image to the right shows a scientist's view of how magnetic reversals look when in the process of switching.

Above: Supercomputer models of Earth's magnetic field  Above: Supercomputer models of Earth's magnetic field. On the left is a normal dipolar magnetic field, typical of the long years between polarity reversals. On the right is the sort of complicated magnetic field Earth has during the upheaval of a reversal                                                                                                                                                          

The Theory of Plate Tectonics The theory that the Earth’s lithosphere is divided into tectonic plates that move. A theory devised to explain both continental drift and sea-floor spreading. A. Tectonic Plate Boundaries – the Earth’s plates move at different speeds and directions. 1. Convergent Boundary- when two tectonic plates push together, where they meet is the boundary A boundary where crustal plates collide with each other Continental-continental

The Theory of Plate Tectonics cont. a. continental/ continental b. continental/ oceanic c. oceanic/ oceanic Oceanic - continental Oceanic-oceanic

The Theory of Plate Tectonics cont. 2. Divergent Boundary – when two tectonic plates move away from each other a. mid-ocean ridges b. can occur on continents too c. earthquakes occur

The Theory of Plate Tectonics cont. 3. Transform Boundary – when tectonic plates slide past each other example: San Andreas Fault (Pacific plate and the North American plate slide past each other)

San Andreas Fault

San Andreas Fault

The Theory of Plate Tectonics cont. B. Three Possible Causes of Plate Motion 1. Ridge Push- an oceanic plate slides under continental lithosphere 2. Convection – hot material from deep inside the Earth rises while cooler material near the surface sinks. 3. Slab Pull – the denser oceanic lithosphere plate sinks and pulls the rest of the tectonic plate with it.

The Theory of Plate Tectonics cont. C. Tracking Plate Motion 1. Plate move at different rates depending on type of plate, shape of plate, and interactions with the plates around it. 2. Measurement can be done at surface level, example: San Andreas Fault 3. The Global Positioning System (GPS): measures the rate of plate movements by continuously sending radio signals via satellites GPS receiver

Deforming the Earth’s Crust Earth’s crust changes due to stress is called deformation. A. Three Types of Stress (or forces) that change the Earth’s Crust 1. Compression- force push together, or squeeze. * occurs at convergent boundaries ex. Rocky Mountains & The Cascade Range formed this way.

Deforming the Earth’s Crust cont. 2. Tension – push or pull away from each other along a single line of motion * occurs at divergent boundaries * example: ground splits in an Earthquake 3. Shear – pull in opposite directions

Deforming the Earth’s Crust cont. Anticline fold B. Folding – occurs when rock layers for due to bends in the Earth’s crust. 1. anticline- upward fold 2. syncline – downward fold 3. monocline – both ends of the fold are still horizontal Syncline fold Monocline fold

Deforming the Earth’s Crust cont. C. Faulting- a fracture or break in the surface 1. There are two sides to a fault (fracture or break) a. hanging wall – part that is above the fault b. footwall – part below the fault 2. Three Types of Faults a. Normal Fault – *hanging wall moves down relative to footwall *when rocks pulled apart due to tension normal fault

Deforming the Earth’s Crust cont. b. Reverse Fault – *hanging wall move up in relation to footwall *when rocks are pushed together by compression c. Lateral Fault / Strike Slip– * Movement horizontal to the right or left

Deforming the Earth’s Crust cont. D. Land forms and Mountain Building 1. Folded Mountains – form when rock layers squeeze together and are pushed upward. ex/. Appalachian Mountains 2. Fault-block Mountains – form when normal faults cause large blocks of the Earth’s crust to drop relative to other blocks. ex. Tetons (in Wyoming) 3. Volcanic Mountains – formed when molten rock erupts. Ex. Mt. Hood

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