Plate Tectonics

Question 1

How old is the earth?

Answer 1

Over 4.5 billion years old

Question 2

Name the structure of the earth in order from exterior to the centre

Answer 2

Crust- oceanic and continental
Mantle or asthenosphere
Outer core
Inner core

Question 3

Name the characteristics of the crust

Answer 3

• 0-70km thick, coolest and least dense rock
• rocks are rich in sodium, silicon, aluminium and potassium
• it’s divided into continental crust and oceanic crust

Question 4

What are the properties of continental crust?

Answer 4

• it’s old, over 1500 million years old
• it’s permanent
• less dense
• mainly granite, silicon, aluminium and oxygen

Question 5

What are the properties of oceanic crust?

Answer 5

• younger, less than 200 million years old
• it is created so it can be destroyed
• 6-10km thick and is denser so it can sink
• mainly basalt silicon magnesium and oxygen

Question 6

What are the properties of the mantle?

Answer 6

• 2900km thick
• apart from the rigid upper mantle, most of the mantle is semi molten containing lighter elements of silicon and oxygen
• temperatures reach 5,000 degrees C and generate convection currents

Question 7

What are the properties of the core (inner and outer)?

Answer 7

• hottest part of the earth, over 5,000 degrees C
• outer part is liquid and the inner is solid
• the inner is made from iron and nickel ore

Question 8

What is the name of the discontinuity found at the top of the mantle?

Answer 8

Mohorovicic boundary

Question 9

What does the mohorovicic boundary do?

Answer 9

Separates the mantle from the crust

Question 10

The crust and part of the mantle beneath form…

Answer 10

Large plate like areas of the lithosphere which float upon the soft and ductile material known and the asthenosphere

Question 11

What are the crust and the upper most part of the mantle?

Answer 11

A single unit

Question 12

What are the two processes that heat from the core is produced?

Answer 12

• Primordial heat left over from the earths creation

- Radiogenic heat produced by the radioactive decay of isotopes

Question 13

What isotopes contribute to the radioactive decay?

Answer 13

Uranium -238
Thorium- 232
Potassium-40

Question 14

What does the theory of plate tectonics help us understand?

Answer 14

• distribution of the worlds major landforms
• where natural hazards can strike
• the distribution of minerals and energy supplies

Question 15

How many plates is the earth made up of?

Answer 15

16

Question 16

Do plates move? If so, how much?

Answer 16

Yes, a few centimetres per year

Question 17

What was the earth beloved to be like 300 million years ago?

Answer 17

One super continent called Pangea

Question 18

In the 16th century, who was the first to recognise the continents could be fitted together?

Answer 18

Francis Bacon

Question 19

Who came up with the idea of continental drift in the 20th century?

Answer 19

Alfred Wegener

Question 20

When did wegener state the plates began to move apart?

Answer 20

In the Carboniferous age 250 million years ago to sometime in the Pleistocene age about 1 million years ago it was a single continent that began breaking up and drifting apart

Question 21

What evidence supports wegener’s theory of continental drift?

Answer 21

• Rare fossils found in rock across oceans in different continents
• glaciations affected different areas becoming contiguous if the continents are fitted back together
• rocks, mountain ranges and fold belts are all consistent within the reconstructed super continent

Question 22

What was discovered during the 1960’s-70’s that caused doubts in Wegeners theory?

Answer 22

• when volcanic rocks cool they adopt a magnetic orientation which reflects the earth magnetic field
• when taking a transept along the ocean floor, it was found that rocks paleognetism vary, like the ocean floor was formed at different times, patterns either side of the oceanic ridge were identical

Question 23

It became clear that rocks relating to each magnetic phase could be traced linearly along the ocean floor, like a band parallel to the ocean ridge so…

Answer 23

It was clear that as the crust of the mid Atlantic ridge split, and the ocean floor moved apart, new rocks were being created in the gap

Question 24

What is another term for a destructive boundary?

Answer 24

Convergent

Question 25

What is another term for a conservative boundary?

Answer 25

Transform

Question 26

What’s another term for a constructive boundary?

Answer 26

Divergent

Question 27

Explain convection currents in the mantle

Answer 27

• Crust isn’t stable so the plates are able to move
• heat in the mantle is obtained through radioactive decays and primordial decay which creates convection currents
• mantle is semi molten so hot liquid rises and it is less dense the cool liquid sinks as it is more dense
• this causes a continuos current which moves the plates above

Question 28

Explain gravitational sliding, ridge push and slab pull

1. The lithosphere thickens with…

Answer 28

…distance and time away from the mid-ocean ridge

Question 29

Explain gravitational sliding, ridge push and slab pull

2. This is because it cools with…

Answer 29

…distance and the boundary between the solid lithosphere and plastic asthenosphere becomes deeper.

Question 30

Explain gravitational sliding, ridge push and slab pull

3. The result of the thickening with distance from the ridges is that…

Answer 30

…the lithosphere/asthenosphere boundary slopes away from the ridge

Question 31

Explain gravitational sliding, ridge push and slab pull

4. Gravity acting on the weight of the lithosphere near the ridge…

Answer 31

…pushes the older part of the plate in front, this is ridge push

Question 32

Explain gravitational sliding, ridge push and slab pull

5. Furthermore, following subduction the lithosphere sinks into…

Answer 32

…the mantle under its own weight, helping to pull the rest of the plate with it, this is slab pull