Plate Tectonics Theory

Question 1

What are the 4 parts of the earth

Answer 1

Core (inner, outer)
Mantle
Crust

Question 2

What is the inner core?

Answer 2

A solid ball made up of lots of iron and nickel

Question 3

What is the outer core?

Answer 3

Semi-Molton, contains lots of iron and nickel

Question 4

What is the mantle made up of

Answer 4

Silicate rocks - rocks that have loads of the element silicon in them

Question 5

Characteristics of mantle

Answer 5

• mantle nearest the core is quite rigid
• layer above this is the asthenosphere - semi-Molton. Can flow
• very top bit is very rigid

Question 6

What is the outer layer of the earth called

Answer 6

Crust

Question 7

What is the rigid top part of the mantle and the crust called

Answer 7

Lithosphere

Question 8

Characteristics of continental crust

Answer 8

Thicker
30-70km thick
Less dense
2.7g/cm3 - density

Question 9

Characteristics of oceanic crust

Answer 9

Thinner
6-10km
More dense
3.0g/cm3 - density

Question 10

Lithosphere is divided into tectonic plates, why do they move

Answer 10

Convection currents in the asthenosphere

Question 11

How do convection currents occur

Answer 11

• radioactive decay of elements in mantle and core (uranium) generates a lot of heat
• when lower parts of asthenosphere heat up, become less dense, slowly rise
• as they rise to the top, they cool down, become more dense, then slowly sink

Question 12

How do convection currents make the plates move

Answer 12

Create drag on the base of the tectonic plates (they’re solid and rigid) which causes them to move

Question 13

When is new crust created

Answer 13

When plates move apart

Question 14

Explain how new crust is created

Answer 14

• convection currents move apart at the base of the lithosphere, causes plates to move apart
• magma rises up to fill gap created, cools to form new crust
• new crust is dragged apart and even more new crust forms between it

Question 15

What happens to the sea floor when plates move apart under the sea

Answer 15

Spreads - sea floor spreading - gets wider

Question 16

What structures are created when plates move apart under the sea

Answer 16

Mid-ocean ridges - ridges of higher terrain on either side of the margin

Question 17

who started the theory of plate tectonics

Answer 17

Alfred Wegner

Question 18

what made people think that there was once one big plate before they started to move apart

Answer 18

in 17th century people noticed South America and Africa looked like they could fit together

Question 19

In 1912, what theory did Alfred Wegener propose?

Answer 19

continental drift

Question 20

what did Wegener propose?

Answer 20

that all continents were once joined together as one super continent called Pangaea which drifted apart

Question 21

what did Wegener base his theory on?

Answer 21

geological evidence and fossil records

he couldn’t back it up with a mechanism that explained how the continents moved

Question 22

in the 1950s, what provided evidence for continental drift?

Answer 22

palaeomagnetism

Question 23

what provided a mechanism for continental drift

Answer 23

sea floor spreading - 1960s

Question 24

what are the 5 different categories that provide evidence for the theory of plate tectonics

Answer 24

• geology
• fossil records
• living species
• climatology
• palaeomagnetism

Question 25

how has geology provided evidence for the theory of plate tectonics

Answer 25

• areas of south america and Africa have rocks of the same age and composition
• can match up the age, rock type and distribution of some mountain ranges e.g. mountains in Norway and Sweden
• these rocks and mountains must’ve formed under the same conditions and in the same place in order to match so well - only possible if continents were once joined

Question 26

how has fossil records provided evidence for the theory of plate tectonics

Answer 26

-can match up the distribution of some fossils by fitting land masses together
unlikely that these species migrated across thousands of mile of water or that they evolved in different places
-fossil records suggest that these places were joined together when these organisms were alive

Question 27

how do living species provide evidence for the theory of plate tectonics

Answer 27

• same living organisms can be found on different continents - unlikely for some to migrate across sea or to have evolved in different locations.
  e. g. earthworms found in New Zealand, Asia, North America

Question 28

how has climatology provided evidence for the theory of plate tectonics

Answer 28

• evidence that the past climates of some continents were similar - once located together
  e. g. similar glacial deposits are found in antarctica, africa, india and australia. fitting places together, you can match up the distribution of deposits-suggests they were joined together

Question 29

What is palaeomagnetism? and what does it provide evidence for?

Answer 29

the study of the history of the earth’s magnetic field. sea floor spreading

Question 30

how often does the earth’s magnetic field reverse polarity?

Answer 30

once every 200,000 years

Question 31

how does palaeomagnetism provide evidence for the theory of plate tectonics?

Answer 31

• magma erupts from mid-ocean ridges, magnetic minerals in molten rock align themselves with direction of earth’s magnetic field
• once new crust has solidified, alignment is fixed
• magnetic minerals in crust created in periods of normal polarity are aligned in opposite direction to those in periods of reverse polarity
• creates alternating bands of magnetic stripes along seafloor
• stripes show crust is getting older, the further away from a mid-ocean ridge you go - plates are moving apart