3.1.5.2 Plate Tectonics

Question 1

What’s the crust

Answer 1

Earth’s outer shell that we live on

Question 2

2 types of crust

Answer 2

Oceanic

Continental

Question 3

What’s the collective name for the crust + upper mantle where tectonic plates are formed

Answer 3

Lithosphere

Question 4

What’s the widest section of the earth called (2900km thick)

Answer 4

Mantle

Question 5

What’s the rock in the upper mantle like

Answer 5

Solid

Sit on top of asthenosphere

Question 6

What’s the asthenosphere

What can it do

Answer 6

Layer of softer, plastic-like rock

Can move very slowly, carrying the lithosphere on top

Question 7

What’s the lower mantle like

Answer 7

Most dense part of mantle

Question 8

What’s the core

Answer 8

The centre + hottest part of the earth - reach 5000*c

Question 9

What’s the core mostly made up of

Answer 9

Iron + nickel

Extremely dense

Question 10

Describe 2 parts of the core

Answer 10

Outer core - semi-liquid and mainly iron

Inner core - solid + made of an iron-nickel alloy

Question 11

What’s the earth’s main internal energy sources

Answer 11

The core - heat producing convection currents

Radioactive decay

Question 12

What are the 2 theory’s for plate tectonics

Answer 12

Wegner’s theory of plate tectonics + continental drift

Hess’s theory of sea-floor spreading

Question 13

Describe wegners theory

Answer 13

A single continent existed about 300 million years ago that he named Pangea + it then later split into 2 continents of Laurasia + Gondwanaland

Further splitting of these land masses formed today’s continents
This is the continental drift theory

Question 14

What did Werner name the single continent

What 2 continents did it split into

Answer 14

Pangea

Laurasia
Gondwanaland

Question 15

2 pieces biological evidence that supported wegners continental drift theory

Answer 15

• fossil brachiopods found in Indian limestone are comparable with similar fossils in Australia
• fossil remains of the mesosaurus reptile are found in South America + South Africa
• fossiled remains of a plant that existed when coal was being formed have even located only in India + Antarctica

Question 16

2 other pieces of evidence that support wegners theory

Answer 16

• bulge of South America fitting into indent below west Africa
• evidence of late-Carboniferous glaciation, deposits from this are found in South America, Antarctica + India
• striations on rocks in Brazil + west Africa
• rock sequences in northern Scotland agree closely with those found in eastern Canada

Question 17

What did Hess discover + study to suggest that sea-floor spreading was occuring

Answer 17

The mid-Atlantic ridge

Question 18

What’s Hess’ evidence sea-floor spreading was occuring

Answer 18

The alternating polarity of the rocks that form the oceanic crust

• iron particles in lava on ocean floor are aligned with earth’s magnetic field
• as lavas solidify, these particles give a permanent record for earth’s polarity at time of eruption
• but at regular intervals, earth’s polarity reverses, resulting in a series of magnetic ‘stripes’ with rocks aligned alternatively towards north + south poles

Question 19

What pattern that Hess saw, suggests the oceanic crust is slowly spreading away from this boundary

Answer 19

The striped pattern, mirrored exactly on each side of the mid-oceanic ridge

Question 20

With distance from the mid-oceanic ridge, what happens to oceanic crust

Answer 20

It gets older

Question 21

What does sea-floor spreading imply

But what must actually be happening

Answer 21

Earth must be getting bigger

But actually, plates must be being destroyed somewhere to accommodate their increase in size at mid-oceanic ridges

Question 22

What are the 7 major plates

Answer 22

African plate
Antarctic plate
Eurasian plate
Pacific plate
Indo-Australian plate
North American plate
South American plate

Question 23

What are the 8 minor plates

Answer 23

Arabian plate
Caribbean plate
Cocos plate
Nazca plate
Juan de Fuca plate
Philippine sea plate
Scotia plate
Okhotsk plate

Question 24

3 plates where there are destructive margins

Answer 24

Pacific plate
South American plate
Caribbean plate

Question 25

2 plates that are diverging (constructive)

Answer 25

Pacific plate + Nazca plate

Question 26

Where’s the main collision margin

Answer 26

Arabian plate

Question 27

3 factors about the oceanic crust

Answer 27

• thinner
• young
• heavier + more dense

Question 28

3 factors about the continental crust

Answer 28

• thicker
• older
• lighter + less dense

Question 29

What’s the oceanic crust made up of

Answer 29

Basalt - silicon, magnesium + oxygen (SIMA)

Question 30

What’s the continental crust made up of

Answer 30

Granite - silicon, aluminium, oxygen (SIAL)

Question 31

What was the generally accepted view of plate movement

Explain

Answer 31

It’s due to convection currents

Convection currents Move apart -> plates move apart
Convection currents converge -> plates converge

Question 32

What’s ridge push

Answer 32

Forces pushing from the ridge, dragging plates down at trenches ‘ acting along sides of plate at conservative margins

Question 33

What produces the ocean ridge at constructive margins (ridge push)

Answer 33

Upwelling of hot magma at ocean ridges generates a buoyancy effect that produces ocean ridges, 2-3km above ocean floor

Question 34

What’s gravitational sliding

Answer 34

Due to gravity, oceanic plates experience a force that acts away from the ridge -> sliding away

Question 35

What’s slab pull

Answer 35

Cool,thick oceanic lithosphere is gravitationally unstable as it’s denser than the asthenosphere
As the plate descends under the continental plate, a gravity generated force pulls the whole oceanic plate down due to the plate’s negative buoyancy

Question 36

3 forces plates are controlled by

Answer 36

Convection currents
Ridge push + gravitational sliding
Slab pull