Plate Tectonics and Continental Drift

Question 1

What are the 5 pieces of evidence for continental drift?

Answer 1

1. similar COASTLINES of Africa and South America
2. GLACIATION in now tropical locations
3. DESERT SAND in now moist and temperate climates
4. TROPICAL PLANTS in Antarctic
5. FOSSIL remains of organisms in restricted areas now widely separated

Question 2

Who was the first person to suggest the concept of continental drift?

Answer 2

Alfred Wegener

Question 3

TRUE or FALSE: when minerals are at such high temperatures that they become magma, they remain magnetic.

Answer 3

FALSE

Question 4

TRUE or FALSE: Earth’s magnetic field lines are uniform and only run N-S.

Answer 4

FALSE: they also vary in dip with latitude

Question 5

What is a polar-wander curve?

Answer 5

magnetized rocks of different ages on a single continent point to different apparent pole positions –> looks like poles moved across time

(note: we now know the poles didn’t move)

Question 6

Did the poles move across time? If not, why can we observe polar-wander curves today?

Answer 6

poles did not move; continents moved

Question 7

What is the name given to the single large continent from 200 million years ago?

Answer 7

Pangaea

Question 8

What is magnetic reversal? What happened to rocks that formed during these reversals?

Answer 8

magnetic reversal: magnetic north changed throughout time –> rocks forming when the magnetic fields was oriented the opposite way are reversely magnetized

Question 9

What geological features can be used to observe the Earth’s magnetic reversal?

Answer 9

volcanoes, mid-ocean ridges

Question 10

What is the difference between a geomagnetic excursion and a geomagnetic reversla?

Answer 10

excursion: variation in pole orientation of up to 45 degrees
reversal: permanent re-orientation of the large-scale field

Question 11

Is the Earth exposed to more solar wind when the Earth is reversely magnetized or normally magnetized?

Answer 11

reversely oriented field –> more solar wind glare

Question 12

How is seafloor spreading used to explain Earth’s magnetism?

Answer 12

newly formed basalts contain ferromagnesian minerals that become magnetic when cool –> record of magnetism is recorded as basalt is continuously extruded at mid-ocean ridges (as magnetism is changes throughout time)

Question 13

What is the formula used to calculate the speed of seafloor spreading?

Answer 13

speed = distance/time

Question 14

What is the range of seafloor spreading rates per year?

Answer 14

0.5 - 20 cm per year

Question 15

How much new seafloor is created each year on average?

Answer 15

3 square km

Question 16

Why is it easier to drill in the sea rather than on land?

Answer 16

the crust is thinner in the ocean

Question 17

What are 4 pieces of evidence that have confirmed sea floor spreading?

Answer 17

1) dating of seafloor by fossil study
2) radiometric dating of rocks sampled by seafloor drilling
3) oceanic rust is youngest at the ridges, older away from the ridge
4) sediments thicken away from the ridge

Question 18

Which layer of the Earth is broken up into plates?

Answer 18

lithosphere

Question 19

Which layer of the Earth do the plates ride on? (i.e. which layer is in motion?)

Answer 19

asthenosphere

Question 20

Which layer of the Earth is solid and rigid?

Answer 20

lithosphere

Question 21

Which layer of the Earth is plastic and partly molten?

Answer 21

asthenosphere

Question 22

What are the 3 plate boundary types?

Answer 22

convergent, divergent, transform

Question 23

How many large plates are there?

Answer 23

fewer than a dozen

Question 24

Why do plates move? Explain.

Answer 24

Convection –> rising hot magma at mid-ocean ridges builds up new lithosphere, eventually sinks back into mantle and is remelted

Question 25

Which type of boundary results in seafloor spreading?

Answer 25

divergent boundary

Question 26

What controls the composition of seawater? Which type of boundary is involved?

Answer 26

divergent boundary –> seafloor spreading –> black smokers –> chemical exchange between basalt and water controls seawater composition

Question 27

How hot is a black smoker?

Answer 27

over 300 degrees celcius

Question 28

A food chain that survives without sunlight is _____________.

Answer 28

lithotrophic

Question 29

Where do lithotrophic food chains exist?

Answer 29

volcanoes (e.g. black smokers)

Question 30

At a convergent boundary between an oceanic plate and a continental plate, which one sinks? Why? What is this process called?

Answer 30

SUBDUCTION: oceanic plate sinks because its density is more similar to asthenosphere

Question 31

__________ volcanoes form at subduction zones.

Answer 31

Andesite

Question 32

What geological feature forms at convergent boundaries between an oceanic and continental plate?

Answer 32

mountains

Question 33

Which contains more SiO2?

a) Andesite volcanoes
b) seafloor basalts

Answer 33

a) Andesite volcanoes

Question 34

At a convergent boundary between an continental plate and a continental plate, which one sinks? What land feature does this form?

Answer 34

neither sink because they are too buoyant; form mountain chain

Question 35

Which type of plate boundary causes earthquakes?

Answer 35

transform boundaries

Question 36

What are mantle plumes?

Answer 36

jets of hot material rising form deep in the mantle

Question 37

How can mantle plumes record plate movement?

Answer 37

• mantle plumes are stationary
• as plates move over the mantle plume, it creates a hot spot trail of progressively older volcanoes
• hot spot trail and volcano age record plate movement

Question 38

Which website is used for earthquake updates?

Answer 38

USGS