lecture 17 - 19

Question 1

what causes an earthquake?

Answer 1

a slow build up of pressure within crustal rocks. if this pressure is suddenly released then parts of the surface may experience a jerking movement

Question 2

difference between the focus and epicentre of an earthquake

Answer 2

the focus is the point at which the release in pressure occurs, and the epicentre is the point on the surface that receives the worst shock

Question 3

how do we know what the earths core looks like?

Answer 3

with the use of seismic , primary and secondary waves

Question 4

explain primary waves

Answer 4

compression waves that travel through any medium
particles vibrate parallel to wave direction
travels fastest

Question 5

what are secondary/shear waves

Answer 5

transverse waves that travel through any liquid.
wave at right angle to particle vibration
travel slower

Question 6

what did Francis Bacon and Alfred Wegener contribute to the theory of continental drift

Answer 6

Francis Bacon noted that Africa fits with the South America continent
Alfred suggested theory of continental drift and existence of a Pangaea in the past, but unable to suggest a mechanism

Question 7

list and explain 6 pieces of evidence that support the theory of continental drift?

Answer 7

1) Fossils - of mesasorus found common in both South Africa and Brazil
2) Geological Evidence - rocks of similar age, type and structure found in SA and Brazil, and also North America and Europe
3) Coal deposits - found under ice caps and glaciation scars in warm areas
4) Mid Atlantic ridge - the 1000km wide and 2.5km high mountain range was found to be consisting of volcanic and recent in origin rock formation
5) Evidence of earths magnetic poles having reversed 171 times over the past 76million years
6) evidence of sea floor spreading

Question 8

Pangaea?

Answer 8

theory of all the earths continents forming one super continent during the Jurassic period almost 200 million years ago

Question 9

describe the different layers of earth

Answer 9

1)Earths Crust
made up of the oceanic and continental crust
- Oceanic Crust consists of mainly basalt and averages 6-10 km in thickness
-Continental Crust consists of older, lighter granite type rock and averages 70km thick

Question 10

what causes tectonic plates to move

Answer 10

convection cell currents

Question 11

explain why crustal plates move

Answer 11

Tectonic plates move because they are floating on top of the liquid mantle. The mantle itself moves due to convection currents: hot rock rises, gives off some heat, then falls. This creates vast swirls of moving liquid rock under the crust of the earth, which moves the plates of crust on top.

Question 12

constructive margins?

Answer 12

2 plates move away forming new oceanic crust with ridges and volcanoes. example: mid atlantic ridge

Question 13

Destructive Margins

Answer 13

oceanic plate moves towards the continental plate, and because oceanic is heavier, it sinks and is destroyed, forming deep sea trenches and island arcs. Example: Nazka sinks under South America

Question 14

Collision Zones

Answer 14

2 continental crusts collide, both rise to form fold mountains. Example: indian vs Eurasian plate forming the Himalayas

Question 15

Passive Margins/transform faults

Answer 15

2 plates move sideways past one another, land is neither formed or destroyed . Example: San Andreas Fault

Question 16

litosphere

Answer 16

earths crust and the rigid upper layer of the mantle

Question 17

asthenosphere

Answer 17

remainder of the mantle after the upper rigid layer

Question 18

moho discontinuity

Answer 18

junction between the earths crust and the mantle where seismic waves are modified