Plate Tectonics

Question 1

Continental drift

Answer 1

Theory proposed by Alfred Wegener 1912. That continents were once connected to each other as a landmass called Pangaea.

Question 2

What are the 2 main observations that Wegener’s conclusions were based on?

Answer 2

Continents fit together like a jigsaw, prehistoric fossils found on countries far away from each other.

Question 3

Why didn’t many scientists first agree with Wegener’s theory?

Answer 3

There was no way to measure if the continents were moving and there was no known force to move such large landmasses.

Question 4

Seafloor spreading

Answer 4

Theory proposed by Harry Hess 1962 to explain mid ocean ridges and the great global rift system. That new rocky crust was being formed at the edges of ridges and spreading outwards, crust subjecting and forming ocean trenches.

Question 5

What are the 3 pieces of evidence that supported the theory of seafloor spreading?

Answer 5

Magnetic striping, age of the sea floor, sediment thickness

Question 6

What is magnetic striping?

Answer 6

Patterns of strips of rocks with alternating magnetism parallel to mid ocean ridges with patterns symmetrical on each side of the ridge.

Question 7

How did magnetic striping support Hess’ theory?

Answer 7

They concluded that there were great cracks in the crust and that magma rose up to fill the cracks and form new crust, which was added equally on each side of the ridge.

Question 8

How did the age of the sea floor support Hess’ theory?

Answer 8

The further the rocks were from the ridges the older they were, suggesting new crust was being formed at the ridges and spreading out.

Rocks on the seafloor were much younger than rocks found on the continents

Question 9

How did sediment thickness support Hess’ theory?

Answer 9

The crust further from the mid ocean ridges was thicker and ad gathered more sediment, suggesting it was older

Question 10

What is each section of the crust called?

Answer 10

A tectonic plate

Question 11

What are all the layers of the earth?

Answer 11

Crust (outermost, solid layer), lithosphere (crust and upper mantle together), asthenosphere (semi solid ‘plastic layer’), core (dense, many iron and nickel) outer core (liquid, flows), inner core (solid)

Question 12

What are the two theories for how plates move?

Answer 12

1. Plates are dragged as hot magma rises up and foes under the plates, creating convection currents, the friction between the plates and flowing magma causes them to move.
2. The force of gravity in either slab pull or ridge push.

Question 13

What is slab pull?

Answer 13

Since the ocean crust in denser at subduction zones, gravity pulls the plate downwards at the subduction zone and away from mid ocean ridges.

Question 14

What is ridge push?

Answer 14

New crust forms at the ridges above the old crust and gravity pulls the new crust downwards, pushing older crust underneath and squeezes plates sideways.

Question 15

What was the believed process that continents split up by and how did it work?

Answer 15

Rifting, the crust cracked and subsided, allowing in water from the ocean. Then seafloor spreading occurred. The continents moved along with the ocean floor that was between them.

Question 16

What are the 2 types of crust? compare and contrast

Answer 16

Oceanic thinner and denser (contains heavier elements) , continental thicker and less dense with lighter elements

Question 17

What are the 3 types of plate boundaries?

Answer 17

Diverging, converging and transform

Question 18

What are diverging boundaries?

Answer 18

Plates that are moving in opposite directions, away from each other. They leave a rift between them,magma rises into the rift and solidifies as it cools and forms new crust. (constructive boundaries)

Question 19

What are converging boundaries?

Answer 19

Plates that are moving towards each other and colliding, rock is destroyed (destructive boundaries). Form mountains, tenches, and chains of islands.

Question 20

How are fold mountains and volcanoes formed?

Answer 20

When oceanic crust collides with continental crust and the oceanic crusts subducts, the continental crust becomes distorted and folds, forming fold mountains and volcanoes.

Question 21

How are trenches formed?

Answer 21

Where an oceanic plate subducts underneath a continental plate, a deep depression in the crust is formed called a trench

Question 22

How are high mountain systems formed?

Answer 22

When 2 continental plates collide, both are pushed upwards because they have similar densities

Question 23

How are island arcs formed?

Answer 23

When 2 oceanic plates collide, the faster moving plate subducts and forms a trench. The descending plate melts to form magma which rises up to the surface creating a chain of volcanic islands.

Question 24

What is a transform boundary?

Answer 24

Two plates are sliding parallel to each other in opposite directions. Usually travel slowly then slip quickly past each other with force. Causes earthquakes, fold mountains and fault lines

Question 25

What are fault lines?

Answer 25

Cracks in the rock at transform boundaries, usually not one continuous crack but many parallel to each other.

Question 26

What is a volcano?

Answer 26

A place where extremely hot material from inside the Earth erupts at its surface.

Question 27

What are examples of the material that erupts from a volcano?

Answer 27

gas, ash, lava, lumps of solid rock

Question 28

When do volcanoes form?

Answer 28

When magma is formed at weak spots in Earth’s crust. It is pushed upwards wit great force into the volcano

Question 29

Why are most volcanoes at plate boundaries?

Answer 29

Because they cause weaknesses in the crust and generate heat to melt rock

Question 30

How do diverging plate boundaries weaken the crust and form volcanoes?

Answer 30

They thin the crust and lower the force on the rock in the asthenosphere and they melt and rise through weaknesses.

Question 31

What are hot spots?

Answer 31

Isolated weak spots in the crust not at plate boundaries where a lot of hot magma is being created

Question 32

What are the 2 possible origins of the magma formed at hot spots?

Answer 32

Heat escaping in narrow plumes from the mantle and stays in a fixed place.
Magma created where crust is flexing as tectonic plates move.

Question 33

What is an earthquake?

Answer 33

A rapid movement of the ground in a wave motion due to the movement of tectonic plates.

Question 34

How do earthquakes occur?

Answer 34

When the tectonic plates overcome the force of friction and the plates suddenly move.

Question 35

What are seismic waves?

Answer 35

The waves in Earth caused by earthquakes

Question 36

What are the 3 main types of seismic waves?

Answer 36

Primary waves, secondary waves and surface waves

Question 37

What are primary waves (p-waves)?

Answer 37

Longitude waves that travel fast back and forth through the earths crust

Question 38

What are secondary waves (s-waves)?

Answer 38

Transverse waves that travel slightly slower than p-waves up and down through earth

Question 39

What are surface waves?

Answer 39

The slowest waves that travel through the surface and can cause the most destruction

Question 40

Where do the strongest and most earthquakes occur?

Answer 40

At converging boundaries

Question 41

What is the focus of an earthquake?

Answer 41

The place underneath the surface where it starts

Question 42

What is the epicentre of an earthquake?

Answer 42

The place on the surface directly above the focus

Question 43

How is the severity of an earthquake measured?

Answer 43

Using the richter scale- each successive number is 10x more severe, or moment magnitude scale

Question 44

What are the 2 main reasons that Australia is such a stable continent?

Answer 44

The lithosphere is thicker than any other continent, resistant to melting and fracture
Not near plate boundaries were the crust is weakened