Lesson 2 theory of plate tectonics

Starter: What type of plate boundaries are these?

Pacific

North American

Task 1: Do you remember the layers…

Using your tables test your partner on the layers!

Take it in turns, 2 mins questioning each.

2:001:591:581:571:561:551:541:531:521:511:501:491:481:471:461:451:441:431:421:411:401:391:381:371:361:351:341:331:321:311:301:291:281:271:261:251:241:231:221:211:201:191:181:171:161:151:141:131:121:111:101:091:081:071:061:051:041:031:021:011:000:590:580:570:560:550:540:530:520:510:500:490:480:470:460:450:440:430:420:410:400:390:380:370:360:350:340:330:320:310:300:290:280:270:260:250:240:230:220:210:200:190:180:170:160:150:140:130:120:110:100:090:080:070:060:050:040:030:020:01End2:00

Lesson 2 title: The Tectonic Theory

Key Enquiry Question 1: Why are some locations more at risk from tectonic hazards?

Objectives1. To investigate the evidence for continental

drift2. To recognise the importance of Earths

magnetism and seismic waves in discovering the plates theory

3. To understand the importance of such research.

What evidence is there of continental drift?

Think. Pair. Share. 5 minutes

Clue: there are 3 main indicators

1. Fossils

2. Mountain ranges

3. Ice presence/ glacial erosion

5 minutes

Timeline of DiscoveryTracing the Development of the

Theory of Plate Tectonics

Timeline of Discovery

• As you progress through the resources, please add events to your timeline.

• Notice that your version of the timeline has the events already labeled on it.

• Your task is to add how each event supports the theory of plate tectonics.

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1915: Fossil, Rock & Mountain evidence is collected by Wegener

Glacier evidence is collected from the rocks on which glaciers carved as they moved through Africa, South America, Australia & India.

WW1: It is found that there are geologic features on the ocean floor!

1919: Seismic waves determine that the mantle is semi-plastic, so the material is solid, but it can flow like a liquid. It is proposed that convection currents exist in the mantle.

1946: The ocean floor is mapped to reveal ridges, mountains, volcanoes, & trenches.

1954: A world map of volcanic eruptions and earthquake epicenters reveals a world-wide pattern.

1960: Hess & Dietz develop the theory of sea-floor spreading.

1963: Magnetic rock reveals a pattern of spreading away from the center away from the Atlantic Ocean.

1965: Wilson proposes the idea that Earth’s crust is made of giant chunks of rock, called plates.

1983: The first GPS is available for public use. Many GPS monitoring devices are placed all around the world.

Timeline of Evidence Supporting Plate Tectonics

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1915: Alfred Wegener publishes his theory of continental drift, which is based on:-Fossils found oceans apart;-Similar rock formations found on different continents, including glacial deposits & mountains;-Climate evidence from fossils & glacial deposits;-The fit of the continents.

Fossil Evidence Didn’t Match

Fossils of the same green plants have been found on almost all continents, suggesting that they all once had similar climates.

Fossil Evidence Didn’t Match

Fossils of tropical plants have been found on Antarctica and on islands in the Arctic Ocean, suggesting that they may have been much warmer in the past.

Glacial Evidence Didn’t MatchAbout 300 million years ago, glaciers covered the southern hemisphere. The pattern they made as they moved across Earth’s surface doesn’t make sense unless the continents are arranged as Wegener proposed (B).

Glacial Evidence Didn’t Match

Glaciers do not form in oceans, which would have to have happened in the past, to be consistent with the patterns of movement found in the rocks (as shown on the map here with arrows). Instead, glaciers originate on land and move toward the ocean.

Glacial Evidence Didn’t Match

When the continents are re-

arranged, according to Wegener’s

theory of continental drift,

the glacial flow fits with our

understanding of how glaciers move.

Notice the Similarities

Look how similar the two landmasses appear to be when the fossil & glacial

evidence are mapped.

Mountains Formed Together

The areas shown in blue show

mountain ranges that contain similar rock and formed at

the same time. When using

Wegner’s map of Pangaea, these

mountains line up into one major

range.

Rock Evidence for Continental

Drift

Wegener’s map also helps to

explain the similar matching rock

formations found oceans apart.

The Problem with Wegener’s Theory

• The main problem with Wegener’s theory of continental drift was that he could not explain what causes the continents to move.

• Alfred Wegener collected substantial evidence to support his work, but since he could not explain the mechanism responsible for the motion of the land masses, his theory was discounted by most scientists.

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1915: Alfred Wegener publishes his theory of continental drift, which is based on:-Fossils found oceans apart;-Similar rock formations found on different continents, including glacial deposits & mountains;;-Climate evidence from fossils & glacial deposits;-The fit of the continents.

What were people saying

about the movement of

the Earth’s Surface?

The Theory of Continental Drift: The continentsmove through the oceans

Wegener’s theory was not supported by the scientific community.

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World War 1, 1914-1918: Sonar technology developed during the war begins to reveal details about the ocean floor in a very basic way… it is not as flat and feature-less as believed!


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1919: Arthur Holmes develops a theory that explains how the large landmasses on Earth move – convection in the mantle.






Convection Currents

• Now that scientists are aware of the crust that exists under the world’s oceans, it becomes an assumption that not just the continents move, but the ocean floor does, too. Although this theory is still not credible in the scientific community, it is gaining support.

• Arthur Holmes came up with a response to the biggest criticism of Alfred Wegener’s theory of continental drift… convection in the mantle.

Convection Currents• Holmes theorized that convection currents move

through the mantle the same way heated air circulates through a room, and radically reshape the Earth’s surface in the process.

• He proposed that upward convection might lift or even rupture the crust, that lateral movement could propel the crust sideways like a conveyor belt, and that where convection turned downwards, the buoyant continents would crumple up and form mountains.

• Holmes also understood the importance of convection as a mechanism for loss of heat from the Earth and of cooling its deep interior.

Taken from http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_holmes.html

Convection Currents

• A circular pattern that forms when matter (in this case located in the mantle) heats and cools, changing the material’s density

• Thought to be the force responsible for moving Earth’s tectonic plates

• Also known as…

- Convection cells

- Convection cycles

Convection Currents• Holmes’ theory has been updated to include the

more current observations that support his work.

• This includes the fact that the Earth’s mantle is not the exact same temperature throughout.

• The pattern of heat flow is circular, creating cycles of hot, less-dense material rising from near the hotter, outer core and cool (comparatively), more-dense material sinking closer to the crust.

• The motion in the mantle move the tectonic plates resting above. The direction of the convection in the mantle determines how the plate interact.

• How do they know about these layers?

Seismic waves

• Your task: read the info sheet and answer the following questions:

Questions Answers

What is the difference between body and surface waves?

What types of body waves are there?

How did body waves help scientists learn about the earths interior?

Which ones are fastest and can be heard by animals?

What types of surface waves are there?

Which waves cause the most damage during earthquakes?

5 minutes

Body and Surface Waves• Seismic waves are the waves of energy caused by the sudden breaking of rock

within the earth or an explosion. • There are two main types of waves, body waves and surface waves. Body waves

can move through the earths inner layers, but surface waves can only move along the surface of the planet like a ripple.

Surface waves are of a much lower frequency than body waves therefore are easily distinguishable on a seismograph. These waves arrive after body waves but are the ones that cause the most damage. Surface waves include ‘Love waves’ named after A.E.H. Love a Britsh mathematician who worked out the model for this type of wave. These waves move from side to side confined to the surface of the crust.The second type of surface wave is the Rayleigh wave (again a mathematician). These waves roll along the surface like a wave of water in a lake or ocean. This rolling moves the Earth up and down as well as side to side. The majority of the shaking felt during an earthquake is this larger Rayleigh wave.

Body waves include Primary (P) and Secondary (S) waves.Primary waves are the fastest wave and can travel through solids and liquids. They therefore arrive first from an earthquake and can sometimes be heard by animals, such as dogs which sometimes start barking before we feel the quake. S waves are slower and can only move through solid rock,this led scientists to believing the outer core is liquid.

Convection Currents

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1946: Scientists make use of the military’s sonar technology to map the ocean floor. They find the mid-oceanic ridge, as well as mountains, volcanoes & deep ocean trenches.






1919: Arthur Holmes develops a theory that explains how the large landmasses on Earth move –convection in the mantle.

Topography of the Earth’s Surface

Notice the high elevation under the oceans, as shown on this map in dark blue. They are underwater mountain ranges, some are volcanic.

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1954: The first world map of volcanic eruptions and earthquake zones is published








Map of Worldwide Earthquakes & Volcanoes

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1960: Harry Hess & Robert Dietz propose the theory of sea-floor spreading: molten rock (magma) oozes up from the Earth's interior along the mid-oceanic ridges, creating new seafloor that spreads away from the active ridge.








Sea-Floor Spreading

Sea-Floor Spreading

The age of the rock forming on the ocean floor supports Harry Hess’ discovery that the sea-floor is spreading apart. New rock forms along the ridges, then is pushed apart when even newer rock forms.

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1960: Harry Hess & Robert Dietz propose the theory of sea-floor spreading molten rock (magma) oozes up from the Earth's interior along the mid-oceanic ridges, creating new seafloor that spreads away from the active ridge.

1963: A pattern of magnetic-striped rock on the ocean floor that provides evidence to support Hess & Dietz’s theory of sea-floor spreading









Magnetic Evidence

• Also supporting the idea of seafloor spreading are clues from the earth’s magnetic poles.• Think of the earth having a giant magnet in its core.• This creates a north and a south poles on earth. We

provide evidence of these poles when we use a compass.

• Scientists theorize that these poles have reversed several times over the lifespan of the earth. This is supported by the discovery of patterns in minerals and rocks which contain iron (remember, iron is magnetic). Magnetic rocks are “attracted” to the north pole, so they are pulled towards it, and away from the south pole.

Magnetic Evidence• Our planet's magnetic field reverses about once

every 200,000 years on average. However, the time between reversals is highly variable. The last time Earth's magnetic field flipped was 780,000 years ago, according to the geologic record of Earth's polarity.

• Rocks that contain magnetic material record these pole reversals. Since the ocean floor contains continuously forming new rock, evidence of the pole reversals as well as more evidence that the sea-floor is spreading apart exists on the ocean floor.

Magnetic Evidence

Rocks are progressively older as they get further from the spreading center at the mid-oceanic ridge.

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1963: A pattern of magnetic-striped rock on the ocean floor that provides evidence to support Hess’s theory of sea-floor spreading




1965: J. TuzoWilson proposed that the entire crust of Earth is made of separate sections called plates, developing the theory of plate tectonics




1960: Harry Hess & Robert Dietz proposed the theory of sea-floor spreading molten rock (magma) oozes up from the Earth's interior along the mid-oceanic ridges, creating new seafloor that spreads away from the active ridge.


20001975195019251900



1960: Harry Hess & Robert Dietz proposed the theory of sea-floor spreading






1965: J. Tuzo Wilson proposed that the entire lithosphere of Earth is made of separate sections called plates, developing the theory of plate tectonics




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1960: Harry Hess & Robert Dietz proposed the theory of sea-floor spreading



The Theory of Plate Tectonics: Allof Earth’s surface is made of tectonic plates that move, causing major geologic events along the boundaries between them.




1965: J. Tuzo Wilson proposed that the entire lithosphere of Earth is made of separate sections called plates, developing the theory of plate tectonics




1983: GPS becomes available for public use & is able to track movement of Earth’s surface

GPS Tracks Earth’s Surface• Prior to 1983, the Global Positioning System (GPS) was only

used by the military. • Over time, technology advanced, satellites were added to

the fleet that aid in collecting GPS data on Earth, and more and more applications for the information emerged.

• To date, measurements on land can be made within centimeters, giving precise information about the changes to Earth’s surface (among other things).

Why are farmers and military struggling to use their old GPS systems? • Too much movement! Every map is centralized on one

known point. Plate movement however means this ‘known point’ has moved! Therefore putting every other location out of sync!

• For more information visit IRIS GPS Site.

http://www.iris.edu/hq/files/programs/education_and_outreach/aotm/14/1.GPS_Background.pdf

Plate Tectonics

• The Theory of Plate Tectonics states: All of Earth’s surface is made of tectonic plates that move, causing major geologic events along the boundaries between them.

• This is the modern accepted theory that explains significant geological changes to the Earth’s surface.

• It is a revision of the theory of continental drift –closely related but includes information collected since Alfred Wegener’s time.

Why is the theory of plate tectonics such a significant idea in science?

• The theory of plate tectonics tied together the following concepts into a single theory that completely changed the science of geology:

– continental drift,

– seafloor spreading,

–magnetic field reversals and

– convection in the mantle

Why is the theory of plate tectonics such a significant idea in science?

• Geologists finally had one theory that could explain all the different evidence they had accumulated to support previous observation, theories and discoveries. Until then, these ideas were scattered and some-what unrelated.

• Geologists now use the theory of plate tectonics to

– show the relationships between geologic events,

– explain the occurrence of earthquakes & volcanic eruptions, and

– explain the formation of mountain ranges & oceans.

What does the future hold?

Discussion point – The continents will come back together at some point in the future.

What evidence do you have to support or disagree with this statement?

5 minutes discussion time – be prepared to share with the group what your pair has discussed.

HWK: Exam question (10 marks)

Outline the evidence to support the theory of

continental drift.Level 1 (1-4 marks) (Midpoint 3)

Simple statements stating evidence for continental drift.

No specific detail or elaboration provided; or two points discussed well.

Level 2: (5-8 marks) (Midpoint 6)

Specific statements of a range of variations. Elaboration that

demonstrates good understanding of the interrelationships between evidence and clear

categorisation of evidence .

Level 3 (9-10 marks) (Midpoint 9)

A fully developed answer, with good elaboration of a range of evidence. A rounded answer with

good use of case studies and clear structure to the work.

Lesson 2LO: To be able to investigate the development and evidence

for tectonic theory.

Key Enquiry Question 1: Why are some locations more at risk from

tectonic hazards?

Key terms:PalaeomagnetismSea Floor SpreadingBasaltAndesiteRhyolite

Concept Checker: 1.2a. The theory of plate tectonics and its key

elements (the earth’s internal structure, mantle convection, palaeomagnetism and sea floor spreading, subduction and slab pull).

1.2b. The operation of these processes at different plate margins (destructive, constructive, collision and transform).

Education

Lesson 2 theory of plate tectonics