tectonics

Question 1

who proposed the idea of continental drift

Answer 1

Alfred Wegener, 1912 Pangaea
- Asserted Pangaea had broken into pieces were still moving apart - related to the spinning Earth

Question 2

what is density

Answer 2

mass per unit volume

Question 3

what is the density stratification like on earth

Answer 3

denser substances towards the center

Question 4

what kind of waves do earthquakes generate

Answer 4

seismic waves

Question 5

2 types of seismic waves

Answer 5

surface waves - travel along Earth’s surface
body waves - travel through Earth

Question 6

2 types of body waves

Answer 6

• P wave - compressional wave – refracted at density boundaries (travel 2x as fast as S waves in solids )
• S wave – shear wave – cannot pass through liquids

Question 7

what is used to detect and record arrival times and intensity of seismic waves

Answer 7

seismograph

Question 8

what did Oldham discover

Answer 8

“shadow zones” - different waves bend different ways in dense and less dense zones – able to get an idea of planet structure

Question 9

crust characteristics

Answer 9

Earth’s rocky shell ~ 2-75 miles
- form shifting slabs of rock called tectonic plates

Question 10

2 types of crust

Answer 10

Oceanic – basalt
Continental – granite

Question 11

upper mantle characteristics

Answer 11

~400 miles thick
- The rigid top ~40 miles

Question 12

lower mantle characteristics

Answer 12

~ 1400 miles thick
- extends to core – similar composition to asthenosphere, but does not melt due to rapid pressure increase – increases melting point

Question 13

mantle characteristics

Answer 13

Oxygen, iron, magnesium, silicon - ~68% of Earth’s mass, 83% of volume

Question 14

outer core characteristics

Answer 14

~1,400 miles thick
- Mostly iron and nickel

Question 15

inner core characteristics

Answer 15

~ 1,500 miles in diameter
- Mostly iron

Question 16

what factors determine the behaviour of the rock

Answer 16

temperature, pressure, rate at which stress is applied

Question 17

Lithosphere characteristics

Answer 17

~ 44-125 miles depth
- crust + uppermost cool and rigid portion of mantle
- floats on (and is supported by) the denser deformable asthenosphere

Question 18

Asthenosphere characteristics

Answer 18

~ 400 miles depth
- hot, partially melted, slowly flowing

Question 19

upper core characteristics

Answer 19

dense, viscous liquid

Question 20

inner core characteritics

Answer 20

solid, ~6 times denser than crust

Question 21

what is earths internal heat maintained by

Answer 21

radioactive decay
- Heat transfer occurs via conduction (solid materials) + convection (fluids like the mantle)

Question 22

what is buoyancy

Answer 22

Things sink until the same proportion of their volume is submerged – continents do this

Question 23

what is Isostatic equilibrium

Answer 23

erosion of a top of a mountain causes their roots to rise to get equilibrium – cause continental crust to get thinner

Question 24

crustal rock vs asthenosphere differences

Answer 24

• crustal rock is rigid and does not flow at surface temperatures
• Ships adjust to weight changes via buoyancy, but crustal rock cannot

Question 25

what is a fault

Answer 25

When the force of uplift/down-bending exceeds mechanical strength of adjacent rock – the rock will fracture - adjacent rock fragments move vertically toward each other

Question 26

what are the 3 historical debates over Earth’s age

Answer 26

• James Hutton – uniformitarianism
• Controversy with biblical school of thought – catastrophism
• Darwin and Wallace – biological evolution

Question 27

Some interesting observations that led to the sea floor spreading hypothesis

Answer 27

• Many earthquake lines correspond with ocean ridges
• Seismographs indicated deformable, non-rigid layer in North Atlantic upper mantle - shows how tectonic plates can move
• Radiometric dating shows that the ocean floor is about 200 million years old - very young compared to Earth’s age
• Ocean floor sediments thickest at edge of Atlantic, thinnest near ‘Mid-Atlantic Ridge’

Question 28

what are Mid-ocean ridges

Answer 28

spreading centers where oceanic crust forms

Question 29

what are Subduction zones

Answer 29

areas where oceanic crust recycled into mantle

Question 30

what is the sea floor spreading hypothesis and the key observations that support it

Answer 30

explains how new oceanic crust forms and moves across the ocean floor
- Spreading centers were hot
- New oceanic crust cooled and so shrunk in volume and become denser as move from center
- The ocean was thus deeper father from the spreading center

Question 31

what are plate tectonics a combination of

Answer 31

Seafloor spreading + continental drift = plate tectonics

Question 32

who proposed the idea of continental drift

Answer 32

Wilson, 1965

Question 33

what are tectonic plates and how are they formed

Answer 33

• Earth’s lithosphere is divided into separate plates that float on the asthenosphere
• they move over the semi-fluid, deformable asthenosphere
• Heat from Earth’s interior causes the asthenosphere to expand, become less dense, and rise
• Rising material lifts and cracks the crust, creating the edges of tectonic plates.

Question 34

3 ways that tectonic plates interact at plate boundaries

Answer 34

• Divergent
• Convergent
• Transform

Question 35

divergent plate interaction

Answer 35

plates move apart
- where ocean basins are formed (mid-ocean ridge systems)
- can also get continental divergence (rift valley)

Question 36

Convergent plate interaction and its 3 types

Answer 36

plates collide and one moves underneath the other
- Ocean to ocean convergence = Trench, Island arc systems
- Ocean to continent convergence = Trench, Volcanoes
- Continent to continent convergence = Mountains, Earthquakes

Question 37

Transform plate interaction

Answer 37

plates move aside each other

Question 38

what are mantle plumes

Answer 38

continent-sized columns of superheated mantle e.g. Deccan Traps, India; Pacific Northwest
- remain relatively stationary under moving plates

Question 39

what are Hotspots

Answer 39

relatively narrow plumes of magma e.g. Hawai’i; Yellowstone
- remain relatively stationary under moving plates

Question 40

what happens when an oceanic plate moves over a hot spot

Answer 40

Formation of a volcanic island chain