L2A

Question 1

Alfred Webber

Answer 1

• concept of continental drift

- Pangaea

Question 2

Alexander Du Toit

Answer 2

Gondwanaland

Question 3

Evidence for Plate Tectonics

Answer 3

1. The fit of the coastlines of some of the continents. The most obvious of which are the continental margins of eastern South America and Western Africa
2. The similarity of sedimentary rocks and mountain belts on continents that are now far apart
3. The same fossils found on widely separated continents

Question 4

Evidence from Paleomagnetism

Answer 4

Magnetic field caused by electric currents in the conductive material of the core

Question 5

Paleomagnetism

Answer 5

the record of magnetism at the time the rock forms

Question 6

Declination

Answer 6

The angle at which a compass needle makes between the magnetic North Pole and a line drawn to the geographic North Pole. Today this angle is about

Question 7

Inclination

Answer 7

A compass will also show a dip in the vertical direction, which varies with its distance from the magnetic pole. The dip value is always lowest near the equator, and highest near the poles

Question 8

By measuring the paleomagnetism of a rock we can learn

Answer 8

1. Declination gives the apparent direction of the magnetic north pole at the time of magnetization.
2. Inclination gives the distance between the rock and pole at the time of magnetization.

Question 9

Deep sea trenches

Answer 9

Subduction

Question 10

Subduction

Answer 10

ocean crust is pushed back into the mantle underneath other crust

Question 11

Lithosphere

Answer 11

• rigid outermost mantle plus overlying crust
• consists of lithosphere plates that undergo plate tectonic processes
• crust + uppermost mantle

Question 12

Asthenophere

Answer 12

• the part of the upper mantle near the melting point

- flow easily occurs, behaves as a plastic

Question 13

Lithospheric Crust

Answer 13

• Oceanic crust
• Magic rocks (Fe and Mg rich)
• Two averages:
  1. Higher level (Continents)
• Dominated by plains
• Mountain belts limited to narrow linear belts
  2. Lower level (Ocean Basins)
• Much of the sea floor is quite level
• Average depth to the sea floor is over 2 miles, deeper trenches cover small areas

Question 14

Continental crust

Answer 14

Felsic

• less Fe and Mg
• more Na, K, Ca

Question 15

Continental crust

Answer 15

• Up to 70km
• Granite
• up to billions of years old
• density: 2.7 g / cm3

Question 16

Oceanic crust

Answer 16

• Up to 10km
• Mafic (basalt)
• Less than 200MY
• density: 2.9 g / cm3

Question 17

Isostasy

Answer 17

The state of gravitational equilibrium between the earth’s crust and mantle such that the tectonic plates “float” at an elevation which depends on their thickness and density

Question 18

Lithospheric Mantle

Answer 18

Uppermost mantle
Rigid rock
50 to 120 km thick
Distinguished from crust by change in seismic velocity
– distinct composition

Question 19

Plate Movement

Answer 19

The asthenosphere is the zone in the upper mantle that is near the melting point (high temperature but lower pressure). It can flow.

Movement in the asthenosphere can carry plates of lithosphere along with it

The hot convection of the mantle rock by slow creep is the way internal heat of the Earth is released to the surface

Question 20

Ridge Push

Answer 20

• slow creep mantle flow
• Assent of magma and heat pushes the lithosphere up, at mid-ocean ridges the existing ocean crust moves away from the ridge

Question 21

Slab Pull

Answer 21

• slow creep mantle flow
• At the other end of the plate, cold, old, more dense ocean crust sinks into the asthenosphere dragging the rest of the plate with it

Question 22

3 Types of Plate Boundaries

Answer 22

1. Divergent
2. Convergent
3. Shear

Question 23

Divergent

Answer 23

where a plate is pulled apart (divergent boundary, normal fault)

Question 24

Convergent

Answer 24

where 2 plates are coming together (convergent boundary, reverse/thrust)

• Three types:
  1. Ocean-continent
  2. Ocean-ocean
  3. Continent-continent

Question 25

Shear

Answer 25

2 plates slide past one another | - transform boundary, strike slip

Question 26

Transform Plate Boundary

Answer 26

Where two plates slide past one another. Occur primarily at locations along mid-ocean ridges though can be found other places