Plate Tectonics

Question 1

Density of Continental and Oceanic Crust

Answer 1

Continental - 2.7 g/cm^3
Oceanic - 3 g/cm^3

Question 2

What happens in the inner core?

Answer 2

A solid ball made of iron/ nickel

Hot due to pressure and radioactive decay from elements such as uranium which gives off heat when it decomposes

Question 3

Theory of Continental Drift

Answer 3

1912 - Alfred Wegener gathered evidence for Pangea 300 million years ago which then broke up into today’s continents

Question 4

Evidence for Theory of Continental Drift

Answer 4

• Jigsaw fit of South America and West Africa
• Similar glacial deposits in S America, Antarctica, India
• Similar rock sequences in Scotland and Canada
• Comparable fossils in India and Australia
• Mesosaurus fossils in S America and S Africa

Question 5

Plate Tectonic Theory (1960s)

Answer 5

The Earths crust is made up of several rigid plates moving relative to each other

Question 6

Evidence for Plate Tectonic Theory

Answer 6

• Harry Hess theorised sea floor spreading
• Mid Atlantic Ridge discovered
• Palaeomagnetism studies showed there were similar bands of rock with aligning polarity either side of the Mid Atlantic Ridge (evidence of sea floor spreading)

Question 7

Ridge Push/ Gravitational Sliding

Answer 7

Constructive boundaries
Gravity pushing the plates apart down the sloping asthenosphere - widens gap

Question 8

Slab Pull

Answer 8

Destructive Boundaries
Subduction plate sinks into mantle and pulls the rest of the plate, causing further subduction

Question 9

Convection currents

Answer 9

Hotter less dense magma close to the inner core roses, cools further from the heat source and sinks

Question 10

Destructive Boundaries

Answer 10

Oceanic/Continental
- denser oceanic subducts into Benioff Zone

Oceanic/Oceanic
- denser plate subducts

Continental/Continental
- no subduction

Question 11

Destructive Boundaries Landforms

Answer 11

• Fold mountains
• Volcanoes + ocean trench except cont/cont
• Earthquakes

Question 12

Constructive Boundaries

Answer 12

Oceanic/Oceanic
- magma rises in gap
- sea floor spreading
- underwater volcanoes emerge
- ocean ridge

Cont/Cont
- land forced apart
- creates Rift Valley
- volcanoes
- eg Himalayas
- eg East African Rift Valley
- raised parts - horsts
- lowered parts - grabens

Question 13

Conservative

Answer 13

• parallel plates between any crusts
• no subduction + no landforms
• shallow focus earthquakes
• eg San Andreas Fault, California

Question 14

Hotspots

Answer 14

• areas of volcanic activity not on plate boundaries
• theory developed in 1970s
• magma plumes rise from mantle (from localised heating) and burns through weaker crust
• volcanoes and islands
• plume stays in the same place but plates move, creating a chain of islands
• eg Hawaii