Teacher Resource 1

Starter Quiz: Teacher notesWhat do we know and what needs consigning to room 101?Room 101 is a BBC comedy television series based on the radio series of the same name, in which celebrities are invited to discuss their pet hates and persuade the host to consign those hates to oblivion in Room 101. You can watch a clip here.

https://www.youtube.com/watch?v=K0o38vsElOk

Our understanding of plate tectonics is developing all the time. Sometimes the changes are so dramatic that what we thought we knew needs re-thinking. So what do we need to rethink and what do we know for sure? What incorrect or out of date knowledge about Plate Tectonics are we going to consign to Room 101?

Set your learners this refresher quiz to check out what they know and what they need to rethink

Part One: True / False Quiz Statements

1. The outer layer of the Earth is made up of ‘crustal plates’

Answer = False

The accurate term is ‘tectonic plates’ or ‘lithospheric plates’. This is important as tectonic plates comprise more than simply ‘crust’ and this impacts on the interaction and behaviour in relation to other parts of the Earth. Tectonic plates are made of rigid lithosphere around 100 km thick. The lithosphere comprises the crust and the uppermost mantle, which are chemically different but both physically solid and rigid. The crust is around 7 km thick in oceanic areas and averages 35 km thick in continental areas – much thinner than the lithosphere. Plates overlie the ductile asthenosphere beneath, which can flow – so there is a physical boundary between the solid lithosphere and the ductile asthenosphere (which occurs at the 1300°C isotherm).

2. The average rate of sea floor spreading in the Atlantic Ocean is 0.025 metres per year.

Answer = True

Satellite GPS has confirmed evidence of sea-floor spreading rates. The Mid-Atlantic ridge is a slow centre of spreading – whereas the Pacific plate along the East Pacific, which divides several plates (Pacific Cocos, Nazca, and Antarctic plates) is spreading at rates between 0.75 and 0.13 metres per year.

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3. The mantle is semi-solid or semi-liquid.

Answer = False

Many people think the term ‘semi-’ implies around half. The mantle is almost entirely solid, as shown by the fact that it transmits seismic S (shear) waves which can only pass through solid material. There is a zone in the upper mantle between the solid lithosphere above and the solid mantle below, called the asthenosphere that is between 1 and 5% liquid (i.e. is 95–99% solid). The molten material is found as films around the edges of crystals, it allows the solid material of the asthenosphere to flow very slowly. However, the mantle beneath can also flow, even though it is completely solid.

A good analogy is ice that, although solid (and capable of being broken by a hammer) can flow downhill in glaciers. When it is near its melting point it can flow more easily.

4. Tectonic plates move because of convection currents in the mantle.

Answer = False (well probably)

Modern techniques of imaging the Earth’s interior (derived from seismic profiling) have been unable to identify convection cells in the mantle that are sufficiently large to drive plate movement plus the upper part of the mantle (aesthenosphere) is now thought to be too plastic to generate enough friction for any conveyor belt-type movement of plates. Instead, plate movement is thought to be caused by 'slab pull'. Density differences across plates are of key importance. Slab pull occurs at subduction zones where the colder and more dense portions of plates sink into the mantle which pulls the remainder of the plate along. This also causes plates to be pulled apart at divergent margins, which results in the thinning of lithosphere. This in turn leads to a decrease in pressure causing melting of the upper mantle (and upwelling of magma, resulting in both rifting and volcanism at mid-ocean ridges). There is evidence that plumes may exist in the magma however modern evidence does not support early theories involving push by magma injection at divergent margins or plate movement driven by large-scale convection currents. However, exactly how plate movement operates in detail is highly controversial.

5. At destructive margins descending plates melt and create magma at their leading edge due to the frictional heat.

Answer = False

Plates only partially melt and frictional heat does not play any part in the process. The plates do not move fast enough to generate such heat. However the presence of water is very important.

Oceanic plates contain water locked up in the basaltic rock and in the overlying sediments. When these are subducted the water acts to lower the melting point of the rocks, so as they descend into the interior of the Earth and heat up, they melt at a more shallow depth than might be expected if they were dry.

Some textbooks explain magma generation along subduction margins using the common (but outdated) myth of plates melting due to heat generated by ‘friction’ between two plates. However friction would work in an opposing way as pressure raises melting points.

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6. There is a hot, liquid layer within the mantle that is the source for the lava erupted on the surface.

Answer = False

There is no widespread liquid layer within the mantle acting as a source for the lava erupted on the surface and local magma chambers beneath volcanic regions are seldom more than a few kilometres in diameter. The asthenosphere is a zone where the mantle is close to its melting point and behaves as a viscous fluid capable of flowing in its solid state. The strong rigid layer above the asthenosphere, composed of solid upper mantle and crustal rock, is called the lithosphere. This is divided on the surface of the planet into a number of tectonic plates that move independently of one another. Magma is generated when the mantle locally starts to partially melt. Partial melting is initiated by different processes in different tectonic environments such as the release of water from hydrous minerals that have been drawn down the subduction zone which locally lowers the melting temperature.

See reference for more information; Loader P., December 2012 Volcanoes, molten magma, … and a nice cup of tea! School Science Review, vol. 94, (347), Association for Science Education (ASE)

7. Most earthquakes are concentrated along boundaries between major tectonic plates.

Answer = True

This is one of the key pieces of evidence for boundaries.

8. Scientists are able to track the movement of tectonic plates using GPS

Answer = True

Scientists first started using GPS satellites to measure plate tectonics in the 1980s. The precision of GPS satellites gives scientists the means to measure multiple types of plate movements. Researchers install GPS receivers at certain monitoring points and collect data once every year or so, which allows them to measure the slow movement of plates between earthquakes. For the rapid seismic motion that occurs during and after an earthquake, scientists capture the movement using permanent GPS receivers that collect data at a rapid rate.

9. Volcanic island arcs develop along convergent margins on the overriding plate above an oceanic plate which is sinking into the mantle.

Answer = True

10. Accretionary wedges develop along subduction zones where sediments and other rocks are scraped off the descending plate and piled up against the leading edge of the overriding plate.

Answer = True

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Part Two; Multiple Choice Questions

1. Which one of the following mechanisms is now considered to be the most important in explaining the movement of plates?

A Ridge push

B Slab pull

C Convection

D Conduction

E Intrusion

Answer = Slab pull

See explanation above for question 4 of the True/ False Quiz Statements.

2. What is the main topographic feature that is found along the centre of mid-ocean ridges

A Ocean trench

B Island arc

C Submarine mountain ranges

D Rift valley

E Earthquakes

Answer = Rift valley.

Rift valleys divide the submarine mountain ranges. Earthquakes are not topographic features.

3. Which one of the following Islands cannot be linked to processes operating at plate margins?

A Montserrat

B Hawaii

C Iceland

D Aleutian islands

E Japan

Answer = Hawaii

Hawaii as the islands occur over a ‘hot spot’

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4. Which is the deepest ocean trench?

A Japan Trench

B Kuril–Kamchatka Trench

C Philippine Trench

D Mariana Trench

E Tonga Trench

Answer = Mariana Trench

The Mariana Trench in the Pacific Ocean with a maximum depth of 11,034 m

5. Which is the World’s largest volcano?

A Mauna Loa

B Mount St Helens

C Mount Vesuvius

D Mount Pinatubo

E Mauna Kea

Answer = Mauna Kea

The tallest from base to top is Mauna Kea. However, the highest in elevation is Ojos del Salado, in the Andes Mountains, and the most massive in terms of total bulk is Tamu Massif.

6. Which phrase best describes high-standing mountainous areas?

A They experience rapid erosion that thins the crust and causes the area to subside

B They are underlain by greater than average thicknesses of lower density, crustal rocks

C They subside rapidly to compensate for erosion

D They have thicker, higher density, mantle rocks beneath them at shallow depths

E They are found at subduction zones

Answer = They experience rapid erosion that thins the crust and causes the area to subside.

7. Where are Accretionary wedges formed?

A At the edge of the overriding plate facing a subduction zone

B At the base of a passive continental margin

C On the oceanic plate side of a transform fault

D Around oceanic plate volcanoes fed by long-lived hot spots in the mantle

E At a conservative plate margin

Answer = At the edge of the overriding plate facing a subduction zone

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8. Which term applies to the process of mountain building?

A Orogneisses

B Orogeny

C Orthogeny

D Orthogonal

E Orography

Answer = Orogeny

9. Which of the following is not found at subduction zones?

A Deep ocean trenches

B Mid ocean ridges

C Volcanic arcs

D Descending lithosphere

E Volcanoes

Answer = Mid ocean ridges

10. Which of the following is a young, currently rising mountain range that resulted from continental collision?

A Appalachian Mountains

B Grampian Mountains

C Himalayan Mountains

D Laurentian Mountains

E Blue Ridge Mountains

Answer = Himalayan Mountains

Try this Quiz again at the end of the unit. Check out how many more answers you get right and see if you can clearly explain your answers this time!

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