Earth structure, plate tectonics theory: convection currents and sea-floor spreading. Evidence: continental drift and palaeomagnetism.

Question 1

How thick is the crust at oceanic plates?

Answer 1

5km

Question 2

How thick is the crust at continental plates?

Answer 2

30-100km

Question 3

What is the mantle?

Answer 3

a zone of molten silicates and other minerals

Question 4

What is the Asthenosphere?

Answer 4

upper part of the mantle
80km deep
rocks kept in semi-molten state

Question 5

What is the difference in composition between the crust and the mantle?

Answer 5

Asthenosphere contains more iron, magnesium and calcium than the crust

Question 6

The lithosphere

Answer 6

cooler and more rigid than the deep mantle
Broken up into moving plate that contains worlds continents and oceans.
Thought to float on top of underlying asthenosphere.

Question 7

What moves the tectonic plates

Answer 7

convection currents

Question 8

How old are most of the continental plates?

Answer 8

over 1,500 million year old

Question 9

What do the continental plates mostly contain?

Answer 9

silica, aluminium and granites

Question 10

How much of the earths mass does the mantle take up?

Answer 10

2/3

Question 11

What creates the magnetic field?

Answer 11

as the earth rotates, the liquid outer core spins

Question 12

How deep is the outer and inner core?

Answer 12

Outer: 2,200km
Inner: 1,250km

Question 13

How deep is the mantle?

Answer 13

2,900km

Question 14

Why is the outer core liquid?

Answer 14

slightly less pressure than the inner core

Question 15

Why is the inner core solid?

Answer 15

twice as dense as the outer core due to metallic composition rather than stoney.
Metals: 80% iron 20% nickel

Question 16

What is the border between the mantle and core called?

Answer 16

the Gutenburg discontinuity

Question 17

What causes mantle plumes?

Answer 17

decay of radioactive materials in the core that creates a blow torch effect up to the crust.`

Question 18

Who was Alfred Wegner?

Answer 18

German meterologist and first to present the argument supporting continental drift.

Question 19

What was wegners evidence?

Answer 19

the fit of the continents, glacial till deposits, shifting of climatic belts over time.
Later on paleomagnetism, convection currents and sea floor spreading added to it.
Much more steamlined galcial scarring

Question 20

What was the name of the super-continent

Answer 20

Pangea

Question 21

What was his observation about the continents in the southern hemisphere?

Answer 21

that they exhibit an identical pattern of rock and fossils known as the ‘Gondwana sequence’

Question 22

What is Paleomagnetism?

Answer 22

when the hot magma rises to the arths surface and cools, the minerals themselves (magnetite especially) becomes magnetised in alignment with the Earth’s current magnetic field.

Question 23

How does the earths mantle behave?

Answer 23

Plastically

Question 24

Why does hot magma rise at oceanic ridges?

Answer 24

hot magma rises because it is less dense than the surrounding magma.

Question 25

Evidence of sea floor spreading (at the oceanic ridge)

Answer 25

striped pattern is mirror either side, suggests crust is spreading away from the ridge, further away the older the rock.

Question 26

How often does the polarity of the earth reverse?

Answer 26

every 400,000 years.