Theories For Plate Tectonics.

Question 1

Structure of the earth.

Answer 1

It’s made up of four layers.

• the inner core - solid mostly iron
• the outer core - semi molten, mostly iron and nickel.
• mantle - solid upper part, semi molten lower part.
• crust - oceanic and continental, makes up the lithosphere with the upper mantle.

Question 2

Continental drift theories

Answer 2

• Alfred Wegener proposed that all of the continents were originally connected together ( supercontinent called Pangea ).

Question 3

What evidence supports Wegeners theory?

Answer 3

Jigsaw for of South America and Africa.

Fossils

Glacial deposits

Rock type

Question 4

Arthur Holmes convection theory.

Answer 4

• radioactive decay within the core releases heat which rises through the mantle and drives convection currents.

Question 5

Arthur Holmes convection theory. 2

Answer 5

Convection currents act as cells which move tectonic plates.

Question 6

Arthur Holmes convection theory. 3

Answer 6

Tectonic plates are able to move as the lithosphere is able to float above the asthenosphere.

Question 7

The Benioff zone.

Answer 7

Zone of seismicity due to the subduction of oceanic plates.

Question 8

The Benioff zone. 2

Answer 8

The different speeds and movements of rock produce numerous earthquakes.

Question 9

The Benioff zone. 3

Answer 9

The contact between the plates at subduction zones is called thrust / mega-thrust fault.

Question 11

The Benioff zone. 4

Answer 11

Where the plates are locked together, friction builds up until is suddenly releases a mega-thrust earthquake

Question 12

The Benioff zone. 5

Answer 12

Often the leading edge can fault and this can hold for hundreds of years before releasing

Question 13

The Benioff zone. 6

Answer 13

This process of strain, stress and failure is called the ELASTIC REBOUND THEORY.

Question 14

The Benioff zone. 7

Answer 14

Zones where there are locked faults can present a significant tectonic hazard

Question 15

What is subduction?

Answer 15

Process of a plate sinking underneath another one at a convergent plate boundary.

Question 16

What is slab pull?

Answer 16

The oceanic plate being subducted is cold and dense- its own density pulls it down into the mantle.

Question 17

What is gravitational sliding

Answer 17

Constructive margins have elevated altitudes due to the rising heat between them which creates a slope down which oceanic plates slide.

Question 18

Sea floor spreading.

Answer 18

During world war 2 radar technology was used to map out the sea floor which lead to the discovery of ocean ridges and trenches.

Question 19

Harry Hess.

Answer 19

He proposed that the oceans get for their centres via sea floor spreading.

Question 20

Sea floor spreading 2

Answer 20

Sea floor spreading occurs when two oceanic plates move away from each other allowing magma from the mantle to rise up and form new crust ridges, resulting in the sea floor widening.

Question 21

Harry Hess 2

Answer 21

However, Hess requires more evidence to prove his theory.

• this evidence was provided by the study of the magnetic patterns of rocks which can be used to date the age of tectonic crust.

Question 22

Magnetic striping.

Answer 22

British scientists Fred Vine and Drummond Matthews suggested that magnetic striping was due to palaeomagnetism.

Question 23

Magnetic striping. 2

Answer 23

They believed that magma flowing from the mid oceanic ridges preserved the then-current orientation of the earths poles, as the magnetic materials inside the rock lined up with the poles.

Question 24

Magnetic striping. 3

Answer 24

Sea floor spreading carried new oceanic crust away from the ridge.

Question 25

Magnetic striping. 4

Answer 25

Magnetic reversals appear as alternating bonds of polarity on the sea floor.

Question 26

Magnetic striping. 5

Answer 26

These bands were symmetrical on both sides of the mid-oceanic ridges, suggesting that new oceanic crust is being continuously formed at the ridges.