Plate Tectonics (Option A)

Question 1

How many years old is the Earth? How many years do geologists know the most about?

Answer 1

The Earth is around 4600 million years old. Geologists know most about the last 570 million years (the Cambrian period) from dating rocks and fossil records.

Question 2

Name the 3 main sections of the Earth

Answer 2

Core (inner + outer)
Mantle
Crust

Question 3

Describe the inner core

Answer 3

• Centre of the earth
• Hottest part
• Solid
• Made of iron and nickel
• Temperatures up to 6000 degrees
• Like the engine room of Earth

Question 4

Describe the outer core

Answer 4

• Layer surrounding inner core
• Liquid
• Made of iron and nickel
• Extremely hot with temperatures similar to inner core

Question 5

Describe the mantle

Answer 5

• Widest section of earth
• Diameter of approx. 2900km
• Solid
• Asthenosphere (outer edge of mantle) can flow; convection currents operate here

Question 6

Describe the lithosphere

Answer 6

• Above asthenosphere
• Upper mantle and crust form solid layer
• Divided into 8 major plates and several minor plates

Question 7

What is the Moho?

Answer 7

The point where the rocks of the crust meet those of the mantle.
Named after line of change or discontinuity between the two layers.

Question 8

Describe the crust

Answer 8

• Outer layer of earth
• Thin layer between 5-60km
• Solid layer upon which we live

Question 9

Name the 2 types of crust

Answer 9

Continental + Oceanic

Question 10

Describe oceanic crust

Answer 10

Thickness: thin (5-7km)
Rock Density: denser (3-3.3gm/m3)
Rock Type: basaltic SIMA (Silica + Magnesium)
Rock Age: less than 250 million years

Question 11

Describe continental crust

Answer 11

Thickness: thick (10-60km)
Rock Density: less dense (2.7 gm/m3)
Rock Type: granitic SIAL (Silica + Alumina)
Rock Age: from 1000 million years and older

Question 12

What are the 2 theories about the earth’s surface moving?

Answer 12

1. Continental Drift : an old theory + suggested that the earth’s surface moved but couldn’t say why
2. Plate Tectonics: a modern and more sufficient theory as it suggests a mechanism for the movement

Question 13

TIMELINE : 1620

Answer 13

Francis Bacon noted ‘jigsaw’ fit of the continents e.g. South America & Africa

Question 14

TIMELINE : 1912

Answer 14

Alfred Wegener proposed continental drift theory. Today’s map formed one land mass “Pangaea” then split into Laurasia and Gondwanaland, continuing to today’s earth

Question 15

TIMELINE : 1948

Answer 15

Mid-Atlantic Ridge was discovered

Question 16

TIMELINE : 1950s

Answer 16

Paleomagnetism discovered

Question 17

TIMELINE : 1960

Answer 17

Harry Hess’ theory about the sea floor spreading

Question 18

Why was Wegener’s theory not initially accepted and what evidence later on supported it?

Answer 18

He could not explain the theory

Not accepted until the 1950s when discoveries such as paleomagnetism provided strong support for continental drift

Question 19

How long ago was Pangaea one large super continent?

Answer 19

225 million years ago

Question 20

How is the way our world today explained?(i.e how have we moved away from Pangaea)

Answer 20

Wegener’s continental drift theory

Question 21

What evidence did Wegener use for continental drift?

Answer 21

1. the distribution of rock types and mountain chains
2. fossils
3. past climatic evidence

Question 22

EVIDENCE of CD : distribution of rock types and mountain chains

Answer 22

The distribution makes more sense when the separate landmasses were placed together.
E.g. Caledonian epoch created long fold mountains across world

Question 23

EVIDENCE of CD : fossils

Answer 23

Land based reptiles such as freshwater Mesosaurus have been found in South America and the south-west of Africa.

Glossopteris ferns found in similar aged rocks in South America, Africa, India and Antarctica. These are now separated by thousands of miles of water in which these animals and plants could not survive.

Question 24

EVIDENCE of CD : past climatic evidence

Answer 24

These continents had in the past been covered and carved by huge ice sheets.
The direction and flow of such sheets seemed to only make sense when the continents were placed together.

Question 25

EVIDENCE of CD : climatological evidence

Answer 25

Places including America, Svalbard and the U.K. all contain coal deposits of similar age that were formed in tropical conditions. They are no longer in tropical climate zones.

Question 26

Who provided the theory of the sea floor spreading?

Answer 26

Harry Hess

Question 27

Briefly describe Hess’ sea floor spreading theory.

Answer 27

He said there were mid-ocean ridges where the crust was cracked and through which material emerged to create new crust on the seabed.
Elsewhere continents were subducted and therefore crust was destroyed.
THIS EXPLAINED WHY THE EARTH WASN’T GETTING ANY BIGGER OR SMALLER.

Question 28

Evidence for the sea floor spreading

Answer 28

1. Existence of great submarine mountain chains and rift valleys at ocean ridges
2. Younger rocks along mid-ocean ridges which become older with distance
3. Bands of rock have alternating polarity, reflecting repeated reversal of earth’s magnetic field
4. Submarine volcanoes show processes at work e.g. in Surtsey

Question 29

Evidence of crust being destroyed

Answer 29

Crust must be being destroyed as the earth was not expanding overall.
Evidence used for subduction was deep ocean trenches.

Question 30

Continents are pushed apart by ________ .

Answer 30

Ridge-push

Question 31

Subduction of oceanic crust occurs by ______ .

Answer 31

Slab-pull

Question 32

Describe paleomagnetism

Answer 32

• earth’s magnetic pole periodically flips
• iron within magma will orientate in the direction of the magnetic pole at the time of cooling
• moving out from mid ocean ridges there was a symmetrical strips pattern either side of the ridge showing alternating magnetic orientation within rocks

Question 33

What did paleomagnetism lead to?

Answer 33

The revival of the continental drift hypothesis and its transformation into plate tectonics.

Question 34

When was paleomagmetism discovered?

Answer 34

During the 1950s as ships with magnetometers were mapping the ocean floors, a particular pattern began to be revealed.

Question 35

What are convection currents?

Answer 35

Plates that make up the lithosphere are driven by slow flows of molten magma in the asthenosphere called convection currents.

Question 36

What can convection currents cause?

Answer 36

In some areas they can break through the crust causing volcanic activity.

Question 37

What is plate tectonics?

Answer 37

The movement of the plates and the activity inside the earth

Question 38

What do plate tectonics cause?

Answer 38

Earthquakes and volcanoes

Question 39

What is the point where 2 plates meet called?

Answer 39

A plate boundary

Question 40

Name the 3 types of plate boundary

Answer 40

1. Constructive
2. Destructive
3. Conservative

Question 41

What is a constructive plate boundary?

Answer 41

Plates are forced apart allowing new material to be formed by rising magma. Most common at ocean ridges.

Question 42

What is a destructive plate boundary?

Answer 42

Plates are forced together causing one of the plates to be subducted or for both plates to buckle upwards at a collision margin.

Question 43

What is a conservative plate boundary?

Answer 43

Plates slide past each other without crust being formed or destroyed.