Theory of Plate Tectonics

Question 1

Earths structure

Answer 1

• The crust
• The mantle
• The core

Question 2

What are the two types of crust?

Answer 2

Continental (thicker, less dense layer)
Oceanic (Thinner, denser layer)

Question 3

What is the mantle?

Answer 3

• Is between the crust and core and is the widest layer

Question 4

Upper mantle

Answer 4

2 layers:
- Rigid layer (above the asthenosphere) makes up lithosphere
- Asthenosphere (plastic type layer, moves under high pressure)

Question 5

Lower mantle

Answer 5

• Is hotter and denser then upper mantle, intense pressure keeps it solid

Question 6

Core

Answer 6

Made up of two parts:
Inner core - solid centre, mostly composed of iron
Outer core - semi molten, mostly liquid iron and nickel

Question 7

What do scientists believe about the tectonic plate theory

Answer 7

That the plates move, but there is still debate over the mechanisms that cause the movement

Question 8

Theory of Convection currents

Answer 8

• The heat from radioactive decay in the core moves up the mantle
• Creating convection currents, which push up into the spreading mid-ocean ridges
• Forcing them apart called ridge push

Question 9

Seafloor spreading

Answer 9

Palaeomagnetism proves that the sea floor has gradually moved apart at a mid-ocean ridge
- Lava cools and solidifies with the minerals lining up with the magnetic field
- The direction of the minerals on either side is a mirror image

Question 10

Subduction and slab pull

Answer 10

• A subduction zone forms when two plates meet
• The heavier plate subducts underneath the lighter plate
• Oceanic crust cools and it becomes thicker and denser meaning gravity forces lithosphere down into a subduction zone
• As it sinks, it drags/pulls the plate with it (slab pull)

Question 11

Convergent boundary

Answer 11

Oceanic plate & continental plates meet
- The heavier (oceanic plate) subducts under the lighter (continental plate)
- Forming a deep ocean trench in subduction zone
- Deep ocean trenches are found next too land areas
- Both volcanic and and earthquakes occur at this plate boundary
- Oceanic and continental plates cause fold mountains
- (which form highest mountains)
- Long, narrow

Question 12

Divergent boundary

Answer 12

• Mid-Atlantic ridge is an example of a divergent plate boundary
• Both volcanic and earthquakes can occur at this plate boundary
• Magma rises

Question 13

Conservative boundary

Answer 13

• Plates slowly move past each other
• Pressure builds and plates eventually ‘snap’ past each other
• The friction causes earthquakes but not volcanoes
• Land is neither made or destroyed as there is no subduction zone

Question 14

Properties of magma at divergent boundaries

Answer 14

• Earthquakes are shallower
• Eruptions are small & effusive
• Eruptions are usually of basalt lava
• (low gas content, low viscosity, higher temp)

Question 15

Properties of magma at convergent boundaries

Answer 15

• Friction and pressure build up in the Benioff Zone (area where most friction and pressure builds up)
• Causes strong earthquakes
• Volcanic eruptions tend to be explosive as magma is rising its way up to the surface
• These eruptions are usually rhyolite lava:
• (High gas content, high viscosity, low temperature)

Question 16

Properties of magma at conservative boundaries

Answer 16

• ## Plates can stick causing a build up of pressure and powerful earthquakes