Name _______________________ Date - Marden Senior …geoscience.msc.sa.edu.au/library/Plate Tectonics Studen… · Web viewThe word “ tectonic ” means ... which stir this semi-fluid

Name _______________________ Date ___________

The Plate Tectonics TheoryThe words “plate” and “tectonic” have special meanings in Geology:

A plate is one of the several rigid pieces of the earth's crust that together make up the Earth's surface. In other words the Earth’s crust — the outer surface that we live on — is made up of large, rigid pieces called plates.

The word “tectonic” means: relating to the structure of the earth's crust and the large-scale processes, such as earthquakes and volcanic eruptions, that occur within it.

The plate tectonics theory was developed in the 1960s and 1970s. It provides a comprehensive explanation of “how the Earth works.”

The Earth’s crust consists of several rigid plates that are all moving in different directions and at different speeds (from 2 cm to 10 cm per year — about the speed at which your fingernails grow).

The plates are moving around like cars in a demolition derby, which means they sometimes crash together, pull apart, or sideswipe each other. Places where two plates meet are called plate boundaries. Boundaries have different names depending on how the two plates are moving in relationship to each other

Crashing together: Convergent Boundaries, pulling apart: Divergent Boundaries, sideswiping: Transform Boundaries

Figure 1 — The Earth's Major PlatesSource: http://www.docstoc.com/docs/123448255/World-Plate-Tectonic-Map

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1 Name two tectonic processes that occur in the Earth’s crust.

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2 Which of these tectonic processes could you expect to occur near your home? _______________

3 Do you think your home located in the middle of, or near the boundary of a plate?

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Figure 1 shows the names and locations of the Earth’s major plates

Year 9 Plate Tectonics Unit Student Booklet — 5 May 2023

Figure 2 — _____________________________________

Source: http://www.open.edu/openlearn/science-maths-technology/science/geology/what-plate-tectonics

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4 In the table below, write the names of the seven largest plates and name the most significant landmasses and/or oceans within each plate.

You can write the names in any order you like.

NAME OF PLATE MOST SIGNIFICANT LANDMASSES AND/OR OCEANS

Evidence for Plate TectonicsEver since the seventeenth century, several lines of evidence have suggested that the continents have not always occupied their present positions on the Earth’s surface. Major forms of evidence include:

matching of continental edges

matching rock types on different continents

similar fossils found on continents that are now widely separated.

1 Write the appropriate captions below figures 2, 3 and 4 to indicate the form of evidence illustrated in each picture.


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Figure 3 — ____________________________________________________

Adapted from http://www.decodedscience.com/continental-drift-new-study-reviews-the-position-of-continents-after-the-breakup-of-gondwana/31909/2

Figure 4 — ________________________________________Source: http://en.wikipedia.org/wiki/File:Snider-Pellegrini_Wegener_fossil_map.svg

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Rock types and geological structures, such as fold mountain ranges, also continue from one continent to another, although the continents are now many thousands of kilometres apart. For example, Figure 3 shows the relative positions of Australia, Antarctica and India about 165 million years ago. The different colours indicate rock types.

Figure 4 shows that fossils of several land-living organisms have been found on continents that are now separated by oceans.


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Alfred Wegener 1880 - 1930In 1910, Wegener noticed the matching coastlines of the Atlantic continents — they looked on maps as if they had once fitted together. He was not the first to notice this, but it was an idea that would never leave his thoughts. He pursued his studies of the continents and he presented his Continental Drift hypothesis on January 6, 1912. He had analysed either side of the Atlantic Ocean for rock type, geological structures and fossils. He noticed that there was a significant similarity between matching edges of the continents, especially in fossil plants.

He published his ideas in 1915, in ‘The Origin of Continents and Oceans’. They formed the first focused and rational argument for continental drift, arguing that all the continents were once joined together in a single landmass and have drifted apart. Wegener also speculated on sea-floor spreading and the role of the mid-ocean ridges, stating: the Mid-Atlantic Ridge ... zone in which the floor of the Atlantic, as it keeps spreading, is continuously tearing open and making space for fresh, relatively fluid and hot molten rock from depth.

Wegener’s ideas differed radically from the accepted beliefs of the time. Some scientists supported him, but more opposed him. Although Wegener had presented a large amount of observational evidence in support of continental drift, the mechanism remained elusive. The hypothesis was initially met with skepticism from geologists who viewed Wegener, a meteorologist, as an outsider. They were also resistant to change. Wegener often complained of their narrow-mindedness

Long after his untimely death in 1930, and after World War II, Wegener's theories were vindicated by the work of Harry Hess and others. In 1960 Hess proposed the mechanism of sea-floor spreading, which would explain how the continents moved. Newly discovered exploration techniques were employed to support this theory and ultimately, the correctness of Wegener's chief idea as well

1 Describe the forms of evidence that Wegener collected to support his theory that Africa and South America had once fitted together.

______________________________________________________________________________

______________________________________________________________________________

2 State two reasons why the scientific community was reluctant to accept Wegener’s ideas.

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3 Name two of the factors that eventually convinced scientists that Wegener had been correct.

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Activity 1 — Moving Continents PuzzleAt the end of this booklet there is a map of two imaginary continents.

1 Describe two forms of evidence that could be used to determine whether these continents were once joined.

2 The estimated ages of six of the rock units on the two continents are given in the table below.

NAME OF ROCK UNIT A B C X Y Z

ESTIMATED AGE [millions of years

(my)]3.0 1.5 2.5 2.7 4.0 3.2

a. Using the ages of the rocks recorded in the above table, draw lines between the continents on the map connecting any rock units that are opposite rocks with similar ages.

b. In what way do the ages of rock types on the two continents support the idea that these two

continents were once joined?

N.B. Ask you teacher to check your answer to question 2 part a before you cut out the continents.

3 To see if the continents fit, cut them out and glue them in the space below, to make the continent that may once have existed.

Colour your continent, giving matching rock types the same colour.

Ask your teacher to check your work before you glue any pieces in place.


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4 Rock units D and W were not suitable for dating by geologists, but their likely ages can now be inferred.

D. ________________________. W. ________________________


Figure 5 — Structure of the Earth's Crust and InteriorAdapted from: http://www.heritage.nf.ca/environment/geology.html

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Features of he Earth’s crust and InteriorThe Earth has a layered structure, as shown in figure 5.The outermost layer is the crust, which is the solid surface we live on. There are two distinct types of crust — oceanic and continental. Both types of crust are divided into tectonic plates, while the mantle controls the movements of these plates.

1 Label figure 5 to indicate the names and thicknesses of the different layers, together with the nature of the materials they are made of.Select your answers from the information given in the table below. The order of information in each column is random.

LAYER NAMES (RED) LAYER THICKNESSES (KM) (GREEN)

LAYER MATERIALS (BLUE)

Inner core 1,370 Granitic/basaltic

Outer core 6 to 35 Nickel-iron

Crust 2,900 Nickel-iron

Mantle 2,000 BasalticCheck your answers with your teacher.


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Activity 2 — Convection Currents in Water

Aim: To demonstrate convection currents in a fluid — Water.

Apparatus: 250ml beaker, tripod, gauze mat, heat mat, Bunsen burner (or a hot plate), tweezers, potassium permanganate crystals, a red pencil.

Procedure:

1. Set up the heating equipment and beaker containing water as shown in diagram A. Do not start heating the water yet.

2. Use the tweezers to pick up one potassium permanganate crystal.

3 Gently lower the tweezers to the bottom of the beaker and release the crystal. Then carefully remove the tweezers from the water, so that you do not disturb the crystal.

5. Light the Bunsen burner or switch on the .

6. Watch the movement of coloured water as the bottom of the beaker is heated.

7. In diagram B, draw the pattern of coloured water as it rises and then sinks. Label areas of rising and sinking water

Discussion

1. How did the coloured water behave soon after the heat was turned on? _____________________

2 What happened when the coloured water reached the top of the water in the beaker?

______________________________________________________________________________

3 State a general rule about the behaviour of hotter and colder areas in a liquid.


Figure 6 — Convection Currents in the Earth's MantleAdapted from: http://www.heritage.nf.ca/environment/geology.html

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______________________________________________________________________________The Earth’s mantle is solid, but over very long periods of time most of it behaves like plasticine and flows. Heat, generated by radioactive decay and gravitational friction, keeps part of the mantle soft. Molten rock (magma) rises towards the surface of the Earth, cools, and sinks to be reheated far below. The temperature difference between the top and bottom of the mantle causes convection currents, which stir this semi-fluid layer. The uppermost mantle and crust form an outer shell of rigid plates. The plates, and the continents they contain, move across the Earth's surface on the convection currents. Figure 6 illustrates the convection currents in the mantle.

1 The directions of two mantle convection currents are shown in the diagram. Draw arrows on the remaining convection currents to indicate the directions in which the magma is flowing.

2 Label the diagram to indicate the hotter and cooler parts of the mantle.

3 Label the outer layer and the three inner layers of the Earth that are shown on the diagram.


Figure 7 — Features of the Ocean FloorAdapted from: http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_midoceanridges.html

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A Variety of Plate BoundariesMid-ocean Ridges — Constructive Plate Boundaries

Figure 7 shows the sea floor as we would see it if there was no water in the oceans. A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges (chains), typically having a valley known as a rift running along its spine. All the mid-ocean ridges of the world are connected, and they form a single global mid-oceanic ridge system that is part of every ocean. The mid-oceanic ridge system is the longest mountain range in the world, with a total length of about 80,000 km.

1 On figure 7, mark and label the positions of at least 2 areas of the mid-ocean ridge.

It can be seen from figure 7 that some of the mid-ocean ridges are not actually in the centres of the oceans. For example, the mountain chain in the Pacific Ocean is also known as the East Oceanic Rise.

Mid-ocean ridges are constructive, plate boundaries. New lithosphere is formed by eruption of basaltic magma at these boundaries, and the plates are moving apart at approximately 5cm a year. The ridges contain rift valleys where magma is welling up from the mantle and solidifying to form new oceanic crust. They are areas where basaltic volcanoes are common, and shallow-focus earthquakes occur due to the movement of upwelling magma. Figure 8 shows how new oceanic crust is formed at mid-ocean ridges.

Addition of new oceanic crust forces the plates away from each other, thereby separating and moving the continents. This process is known as sea-floor spreading.


Figure 8 — Formation of new Oceanic Crust at a Mid-ocean RidgeSource: Adapted from http://oceansjsu.com/105d/exped_commotion/2.html

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2 On figure 8, mark and label the following features:

Rising magma, new oceanic crust forming, directions of plate movement (or sea-floor spreading), sea level, ocean floor, oceanic crust, upper mantle.

As shown in figure 8, the Earth’s crust and upper mantle consist of two layers, known as the lithosphere and the asthenosphere.

The lithospere is made up of the crust, which is up to about 35km thick and the upper 100m of the mantle. It consists of hard, brittle rock. The asthenosphere comprises the next 100km of the mantle. It consists of rock in a semi-molten (plasticine-like) state, which is constantly being stirred by convection currents.

Destructive Plate Boundaries

Since new oceanic crust is continually being formed at constructive plate boundaries, old oceanic crust must be destroyed elsewhere, because the Earth is not getting any larger.

Destructive plate boundaries are also known as subduction zones, which are regions where one plate is dipping, or subducting, under another and lithosphere is being destroyed. Convection currents in the asthenosphere carry the sea floor in a conveyor-belt fashion to the deep-ocean trenches, where the sea floor descends into the mantle and eventually melts to become part of the mantle


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3 Go back to figure 7. On this map, mark and label at least two examples of deep-ocean trenches.

Destructive boundaries may exist between: Two oceanic plates An oceanic plate and a continental plate Two continental plates

Earthquakes are likely to occur at all three types of destructive boundary, while volcanoes are common at boundaries involving oceanic plates. Figure 9 shows how oceanic crust is destroyed at an example of these boundaries. In this case, an oceanic plate is being destroyed by subduction under a continental plate. The west coast of South America is an example of this type of boundary, forming the Andes mountain range.

Figure 9 — A Destructive Boundary Between an Oceanic Plate and a Continental PlateSource: adapted from http://geography.parkfieldprimary.com/hazards/plate-tectonics

4 On figure 9, label the following features of a destructive plate boundary:

Asthenosphere, oceanic lithosphere, deep-ocean trench, subduction zone, risng magma, volcanoes, fold mountain chain, continental lithosphere, directions of movement of the plates,

Volcanoes occur at these boundaries because the subducting plate melts as it travels deeper into the hot mantle, and the magma rises to be erupted as lava over the Earth’s surface above the subduction zone. Deep- and shallow-focus earthquakes are caused by friction between the subducting plate and the mantle into which it is moving. Compression forces between the two plates cause fold mountain ranges to form

When two oceanic plates collide, magma from the subducting plate erupts at the Earth’s surface to form an arc of volcanic islands, such as the Philippines. When plates are colliding under the sea, earthquakes are likely to occur under the sea, giving rise to destructive tsunamis.


http://geography.parkfieldprimary.com/hazards/plate-tectonics

Figure 10 — A Conservative Plate BoundarySource: Adapted from http://extremeearth.net/education/lithosphere/

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Conservative Plate Boundaries.

No crust is created or destroyed at conservative boundaries between two plates. The plates just slide past each other, as shown in figure 10. No volcanic activity occurs at these boundaries, but earthquakes are caused by friction between the plates as they slide past each other.

Activity 3 —Analysis of a Plate BoundaryIn order to complete questions 1 to 3, you will need access to the Internet.

1 Locate the site with the following URL:

http://rev.seis.sc.edu/earthquakes.html

The circles on the map indicate the locations of earthquakes that have occurred anywhere in the world during the past year.

2 Look at figure 1 of this booklet, or a similar diagram that shows the world’s major tectonic plates.

a. What relationship can you see between the locations of most of the earthquakes and the plate boundaries shown on the map?

__________________________________________________________________

__________________________________________________________________

b. The small pink dots on the map show many of the historically recorded earthquakes.

How do these compare with the locations of plate boundaries on the map?

__________________________________________________________________


http://rev.seis.sc.edu/earthquakes.html

Documents

Name _______________________ Date - Marden Senior …geoscience.msc.sa.edu.au/library/Plate Tectonics Studen… · Web viewThe word “ tectonic ” means ... which stir this semi-fluid