Chapter 17 – Plate Tectonics

http://maps.unomaha.edu/maher/GEOL1010/lecture15/map_plate_tectonics_world.gif

(aka Putting the Pieces Together!)

Chapter 17. 1Drifting Continents

• Describe one piece of early evidence to suggest that Earth’s continents may have once been joined.

• Discuss the evidence of continental drift.

• Explain why continental drift was not accepted when it was first proposed.

Early Mapmakers Many early mapmakers thought Earth’s continents had moved based on matching coastlines.

Some early mapmakers thought that the coastline of South America matched the coastline of Africa.

Alfred Wegener

A meteorologist, by trade.

Wegener’s Evidence The existence of coal beds in

Antarctica indicates that the continent once had a temperate, rainy climate.

Wegener’s Evidence

Glossopteris is a fossil fern that helped support Wegener’s hypothesis of continental drift.

Alfred Wegener

"Doesn't the east coast of South America fit exactly against the west coast of Africa, as if they had once been joined?“ - "This is an

idea I'll have to pursue."

Earth’s continents were once joined as a single landmass called Pangaea.

Pangea

The Argyle Sweater 3/11/11

Science’s Reaction

"Utter, damned rot!" said the president of the prestigious American Philosophical Society. "If we are to believe [this] hypothesis, we must forget everything we have learned in the last 70 years and start all over again," said another American scientist. Anyone who "valued his reputation for scientific sanity" would never dare support such a theory, said a British geologist.

Scientists at the time rejected Wegener’s hypothesis of continental drift because he could not explain how or why Earth’s continents move.

17.1 Quiz

Chapter 17. 2Seafloor Spreading

• Explain the significance of magnetic patterns on the seafloor.

• Explain the process of seafloor spreading.

• Summarize the evidence that led to the discovery of seafloor spreading.

Mapping the Seafloor

Mid-Atlantic Ridge

Isochrons

A map line connecting points that have the same age is an isochron.

Isochrons(continued) Compared to ocean crust near deep-sea

trenches, crusts near ocean ridges are younger .

Paleomagnetism The study of Earth’s magnetic record is known as paleomagnetism.

Paleomagnetism(continued)

The magnetic pattern of ocean-floor rocks on one side of an ocean ridge is a mirror image of that of the other side .

Seafloor Spreading

As new seafloor moves away from an ocean ridge, the seafloor cools and becomes more dense than the material beneath it.

Seafloor Spreading

The seafloor contracts and sinks.

Hot magma which is less dense than surrounding material, is forced toward the crust.

Crust spreads along an ocean ridge and magma fills the gap that is created.

New ocean floor forms as the magma hardens.

New seafloor moves away from the ridge, cools, and becomes more dense than the material beneath it.

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17.2 Quiz

Chapter 17. 3 Theory of Plate Tectonics

• Explain the theory of plate tectonics.

• Compare and contrast the three types of plate boundaries and the features associated with each.

Evidence - Volcanism

Evidence - Earthquakes

The Theory

The theory of plate tectonics states that Earth’s crust and rigid upper mantle are broken into enormous slabs called plates that move slowly over Earth’s surface.

The Theory (Continued)

According to the theory of plate tectonics, plates interact at plate boundaries by coming toward each other, moving away from each other, or moving horizontally past each other.

World Tectonic Map to Label

Earth’s Tectonic Plates

Plate Boundaries

DIVERGENT

CONVERGENT

TRANSFORM

Chapter 17. 3 Illustrations

Chapter 17. 3 Quiz

Plate Motions Through Time

Breakup of Pangaea

Motion at Plate Boundaries

Current Movement &What it will look like?

Chapter 17. 4 Causes of Plate Motion

• Explain the process of convection.• Summarize how convection in the mantle is related to the movements of tectonic plates.

• Compare and contrast the processes of ridge push and slab pull.

Convection

The transfer of thermal energy by the movement of heated matter is convection.

Convection currents transfer thermal energy from warmer regions to cooler regions.

Convection Currents

The driving forces of tectonic plates are related to convection currents in Earth’s mantle.

Convection Currents

Review

Oceanic crust is composed mainly of basalt, and continental crust is composed mainly of granite.

http://www.earth.northwestern.edu/people/seth/107/Gravity/contoceaniso.htm

Slab Pull

The downward part of a convection current causes a sinking force that pulls tectonic plates toward one another .

The weight of a subducting plate helps to pull the lithosphere into a subduction zone in a process called slab pull.

Ridge Push

The rising part of a convection current causes both upward and lateral forces that lift and split the lithosphere at a divergent boundary.

Convection and Tectonics

17.3 Quiz

Chapter 20 – Mountain Building

Before I studied mountains, a mountain was just a mountain.

While I studied mountains, a mountain was so much more than a

mountain.

When I understood mountains, a mountain was just a mountain.

-Zen Saying-

20.1 Crust-MantleRelationships

OBJECTIVES

Describe the elevation distribution of Earth’s surface.

Explain isostasy and how it pertains to Earth’s mountains.

Describe how Earth’s crust responds to the addition and removal of mass.

20.1 Earth’s Topography

Thoughts? What is Earth’s highest elevation?

What is Earth’s lowest elevation?

Majority of Topography

About 70 % of Earth’s surface is below sea level.

Isostasy

Isostasy between Earth’s mantle and crust exists when the mass of crust is balanced as a result of buoyancy and gravity.

Displacement

The seafloor displaces more of the mantle than the same thickness of the continental crust.

http://www.earth.northwestern.edu/people/seth/107/Gravity/contoceaniso.htm

Crust ThicknessContinental crust, because it is thicker than oceanic crust, rises higher above Earth’s surface.

Deepest RootMt. Everest is the tallest mountain on Earth, so it probably has the deepest root.

Isostatic Rebound

When mountains erode, their roots decrease in size.  

In the process of isostatic rebound, mountains are eroded over hundreds of millions of years, while the crust below them rises.

Glacial Isostasy

20.2 Convergent-Boundary Mountains

OBJECTIVES

Compare and contrast the different type of mountains that form along convergent plate boundaries.

Explain how Appalachian Mountains formed.

Orogeny

Orogeny

The process that forms all mountains.

Subduction Zones

Subduction results in the formation of deep-sea trenchs..

Convergent Zones

Oceanic-Oceanic

The volcanoes of an island arc complex form as a result of oceanic-oceanic convergence.

http://www.kabrna.com/cpgs/programme/images05_06/aleutian_arc.jpg

At an oceanic-oceanic convergent boundary, old crust is recycled by subduction.

Convergent Zones

Convergent Zones(continued)

Continental-Continental

plate collisions produce very tall mountain ranges.

The Himalayas formed as the result of continental-continental convergence.

http://www.cartage.org.lb/en/themes/sciences/earthscience/geology/earth/storyplatetectonics/platetectonics/understanding/convergent/Continental/Continental.htm

Convergent Zones(continued)

The tallest orogenic belts are found at continental-continental convergent boundaries.

Convergent Zones(continued)

The Appalachian Mountains are an example of convergent-boundary mountains.

Tectonic Settings and Volcanic Activity

20.2 Quiz

20.3 Other Types of Mountains

OBJECTIVES

Describe the mountain ranges that form along ocean ridges.

Compare and contrast up-lifted and fault-block mountains.

Describe the mountains that form as a result of hot-spots in Earth’s mantle.

Divergent-Boundary Mountains

Features found at divergent boundaries include ocean ridges .

Non-Boundary Mountains – Uplifted

Uplifted mountains form when a large region of Earth’s crust rises up as a unit.

Uplifted (continued)

Uplifted mountains have rocks that are not very deformed.

Uplifted (continued)

Uplifted mountains are the result of erosional forces.

Uplifted (continued)

The Adirondack Mountains, which are made of rocks that show little deformation, are uplifted mountains.

20.3 Non-Boundary Mountains – Fault Block

Fault-block mountains form when a large pieces of crust are dropped between large faults .

Grand Tetons, Wyoming

Non-Boundary Mountains – Volcanic Peaks

Volcanoes that form over hot spots are often solitary and far from tectonic plate boundaries.

The Hawaiian Islands formed as the result of the Pacific Plate’s moving over hot spots in Earth’s mantle.

20.3 Quiz