The Dynamic Earth

Question 1

Internal structure of the earth

Answer 1

THE INNER CORE:

• mostly iron and is solid
• about 1,300 kilometres wide
• temperatures can reach up to 7000º C.

THE OUTER CORE:

• made up of molten iron and nickel
• around 2,250 kilometres thick
• temperatures mostly between 4000º C and 6000º C.

THE MANTLE:

• about 2,900 kilometres wide
• temperatures between 500º C and 2000º C
• made up of partially molten rock and magma

THE CRUST (OR LITHOSPHERE):

• mostly solid rock, which is very strong and rigid
• It includes landforms, rocks and soil.
• varies in thickness, small as 5km to as big as 70km

Question 2

Which scientist developed the Theory of Continental Drift?

Explain his theory.

Answer 2

Alfred Wegner (German meterologist) developed the theory

• theory is about how continents shift position on the Earth’s surface
• originally one ‘supercontinent’ referred to as Pangea
• Eventually Pangea broke up into smaller parts and formed the seven continents

Question 3

Why didn’t fellow scientists believe Wegner’s theory?

Answer 3

• a lack of mechanism
• His assumptions were easily challenged
• didn’t have a clear explanation of how continental drift could have occurred

Question 4

What evidence is ther that Continental Drift occured?

Answer 4

The evidence was the discovery of fossils of the same land animals on different continents.

Question 5

Continetal crust

Answer 5

• the plates that make up the continents/land
• generally between 30 km and 70 km thick

Question 6

Oceanic crust

Answer 6

• plates beneath the ocean
• a lot denser and thinner than continental crust
• average thickness is about 6 km.

Question 7

What causes plates to converge?

Answer 7

Converging plates are caused when two plates push against each other

Question 8

What do we call the boundaries between converging plates?

Answer 8

• They are called destructive plate boundaries
• This is because solid ocean crust melts into the mantle

Question 9

Example of a constructive plate boundary

Answer 9

The Eurasian Plate

Question 10

Example of a destructive plate boundary

Answer 10

The Pacific plate

Question 11

An example where ocean ridges are formed.

Answer 11

Ocean ridges are formed by convection currents rising in the mantle beneath the oceanic crust and creating magma where two tectonic plates meet at a divergent boundary.

Example: Mid-Atlantic ridge

Question 12

An example where subduction occurs.

Answer 12

Subduction occurs when one tectonic plate (at a convergent boundary) moves under another tectonic plate and sinks into the mantle. Areas where this occurs are eknown as subduction zones.

Example: the “ring of fire”

Question 13

FOLDING ROCK - explain and give an example

Answer 13

Occurs when the forces beneath the Earth are so powerful that layers of rock bend and crumple without breaking.

Example: Australia’s Great Dividing Range

Question 14

NORMAL FAULT - explain and give an example

Answer 14

• Occurs when the hanging wall block moves downwards while the footwall block moves upwards
• It is the result of the Earth’s crust spreading apart.

Example: The Long Point–Eureka Heights fault system

Question 15

REVERSE FAULT - explain and give an example

Answer 15

Occur when the hanging wall block moves up while the footwall block moves down

Example: The Sierra Madre fault zone of southern California

Question 16

SLIP FAULT - explain and give an example

Answer 16

Occurs when blocks of crust slide horizontally past each other

Example: The San Andreas Fault in California

Question 17

RIFT VALLEYS - explain and give an example

Answer 17

Occurs between two sunken blocks of crust, where there is a block that has been pushed upwards by the forces below

Example: the Gulf of California Rift Zone.

Question 18

What causes earthquakes?

Answer 18

Earthquakes occur when the Earth’s crust shifts below the surface.

Question 19

What is the epicentre?

Answer 19

The epicentre is the point directly above the focus (the focus is the point below the surface where the movement begins).

Question 20

What scale is used to measure the size of an earthquake?

Answer 20

• The Richter scale
• An earthquake is measured by the amount of energy it releases

Question 21

List the three types of seismic waves

Answer 21

P-WAVES (primary waves):

• compression waves
• fastest of all the Seismic waves
• travel through the body of the Earth the same way that sound waves travel through air

S-WAVES (secondary waves):

• The second set of waves detected after P-waves
• They are transverse waves
• travel through the body of the Earth

L-WAVES:

• These are surface waves
• travel around the Earth
• They are the slowest Seismic waves
• they are responsible for causing the majority of an earthquake’s catastrophic power

Question 22

How are tsunami’s formed?

Answer 22

• First, the rapid movement of the ocean floor (from an earthquake) upsets a column of water.
• This creates enormous waves that travel through the ocean at speeds up to 900 km/h
• As the waves approach land, the water gets shallower which forces the waves’ energy to compress into a smaller space
• Causes the waves to gain height (up to 30 metres high) and slow down
• The wave then breaks at land and causes mass destruction.

Question 23

Explain lava

Answer 23

When magma reaches the surface and expels from the mouth of the volcano, it becomes lava.

Question 24

Explain magma

Answer 24

Magma is red-hot molten rock that is found underneath the Earth’s crust.

Question 25

Active volcano

Answer 25

Active volcanoes erupt frequently or have erupted recently.

Question 26

Dormant volcano

Answer 26

A dormant volcano is an active volcano that has not erupted recently, but is expected to erupt again.

Question 27

Extinct volcano

Answer 27

Extinct volcanoes have not erupted for at least 10,000 years and are highly unlikely to erupt again.