Plate Tectonics

Question 1

How do plates move?

Answer 1

Convection currents form in the upper mantle as molten magma is heated by the high temperatures of the core (6000°C).
As the magma heats, it rises up towards the upper mantle.
As the semi molten magma moves away from the heat of the core, it cools and moves sideways, dragging the plates on top of the ductile asthenosphere (slab pull).
Magma sinks and the process repeats

Question 2

Key points about lithosphere (composition, thickness, properties)

Answer 2

Comprised of crust and upper mantle, solid, 50-100km thick

Question 3

Define endogenic forces

Answer 3

Forces from within the earth that cause the crust to move vertically and horizontally. Convection currents are mainly responsible for endogenic forces.

Question 4

Name major plates on map

Answer 4

N/A

Question 5

Define moho line

Answer 5

The boundary that divides the solid upper mantle and the earth’s crust

Question 6

Key points about inner core (properties-2, temperature)

Answer 6

Solid, magnetized, 6000°C

Question 7

How old is the earth?

Answer 7

Over 4.6 billion years old

Question 8

Define slab pull and draw diagram

Answer 8

Old oceanic crust which is cool and dense, has sunk under another plate into the asthenosphere which pulls the trailing lithosphere along

Question 9

Define lithosphere

Answer 9

The solid upper mantle and crust combined which is broken up into plates

Question 10

Key point about mantle (material, thickness, temp)

Answer 10

Made of of semi molten material , 2,900km thick, 1600°C

Question 11

How were the layers of the earth formed?

Answer 11

When the planet first formed, it was roughly 2000°C and made of mostly molten material. As the earth cooled slowly, the heaviest materials sank to the centre forming the inner core.

Question 12

Key points about outer core (properties, temperature)

Answer 12

Liquid, 4000°C

Question 13

How and when was the Theory of Plate Tectonics formed

Answer 13

In 1968 the Theory of Continental Drift and the Theory of seafloor spreading combined to form the Theory of Plate Tectonics

Question 14

Five differences between continental crust and oceanic crust

Answer 14

Continental: Makes up land, Granite, Properties SIAL (silica and aluminium), Less dense - lighter, 30-80km thick

Oceanic: Makes up ocean floor, Basalt, Properties SIMA (silica and magnesium), Denser - heavier, Roughly 8km thick

Question 15

Explain the theory of Plate Tectonics, and how it explains the forces at work at plate boundaries (30m)

Answer 15

Check notes

Question 16

Explain Theory of Seafloor Spreading

Answer 16

Harry Hess published this theory in 1960. He worked in the US Navy in WWII and used to sonar to map ocean floor where he discovered underwater volcanic mountains. It stated that at certain places the crust splits or fissures and new land is formed under oceans due to upwelling of magma.
Evidence: Age of seafloor - Younger at mid ocean ridges, older at continental shelves and discovery of Mid Atlantic Ridge

Question 17

Define subduction and draw diagram

Answer 17

A geologic process whereby the thinner, heavier oceanic crust is forced under the lighter continental crust and slides beneath it into the mantle where it melts at a depth of 100km

Question 18

Name major plate boundaries on map

Answer 18

N/A

Question 19

Key points about asthenosphere (thickenss, temperature and properties)

Answer 19

100-200km thick, 1200°C, ductile

Question 20

Explain the Theory of Continental Drift

Answer 20

Alfred Wegener, a German meteorologist/geologist published this theory in 1912. It stated that continents drift over time to their current positions and all continents were joined at one time.
His Evidence:
1. Fossils: Mesosaurus (freshwater reptile) fossils found on multiple continents
2. Continental fit: Africa and South America fit like a jigsaw
3. Matching Mountain ranges: USA, Ireland and Scotland - all formed around same time and made of same rock
He was not able to prove his theory and died without recognition in the 1930s

Question 21

Define asthenosphere

Answer 21

Section of the mantle beneath the lithosphere which allows the solid rock above to slide on it - ductile