1. Chapter 4 Plate Tectonics
Earth Science
Chapter 4 Plate Tectonics

2. Evidence from Rock Samples – Direct (you can hold the rocks) Evidence from Seismic Waves – Indirect – speed of waves and their path are studied

3. Pressure - Increases with depth - weight of rock from above
The three main layers of Earth differ in temperature, composition, pressure and size.
Temperature – Temperature increases with depth - heat left over from when earth formed + radioactive elements release heat
Pressure - Increases with depth - weight of rock from above

4. The three main layers of Earth are - the crust, the mantle,
Earth's Interior
The three main layers of Earth are -
the crust,
the mantle,
and the core.
Layers of the Earth are similar to the layers in a hardboiled egg!

5. The Crust Thinner Mostly Basalt (igneous rock)
Solid outer rock – includes land and ocean floor, 5km – 40km thick (can be 70km beneath mountains)
Oceanic Crust
Thinner
Mostly Basalt (igneous rock)
Denser than continental crust
Continental Crust
Thicker
Mostly Granite (igneous rock)
Less dense than oceanic crust

6. The Mantle – 3000km thick Lithosphere – ‘lithos’ = stone (Greek)
Rigid
Uppermost part of mantle and crust
Asthenosphere –
‘asthenes’ = weak
Bendable + softer + can flow
The Lower Mantle
Solid

9. The Core km thick
Mostly iron and nickel Outer Core - liquid Inner Core – dense, solid, extreme pressure squeezes iron and nickel so much that they cannot be liquid

10. Earth’s Magnetic Field
Movements in the earth’s liquid outer core create a magnetic field. This magnetic field surrounds the planet

11. Structure of the earth – http://www. youtube. com/watch
Structure of the earth – Layers of the earth song –

12. Convection and the Mantle 4.2
The movement of energy form a warmer object to a colder object is called Heat Transfer.
There are three types of heat transfer:
Radiation
Conduction
Convection

13. Radiation Heat is transferred through space
No direct contact between heat source and object
sunlight, heat around open fire
Eureka Radiation 4:02 (2:39)

14. Conduction Transfers heat by direct contact Matter touching matter
Can occur between any state of matter: solid, liquid or gas
Metals are good conductors of heat
Bad conductors include wood, rubber, glass
Example: Heat transfers directly from the element of a stove to a metal pot
Eureka Conduction 2:02

15. Conduction -

16. Convection
heat transfer by the movement of currents within fluids – liquids and gasses.
Hotter particles move further apart and rise (less dense)
Cooler particles move closer together and fall (more dense)
Transfer is therefore vertical (up & down)
Caused by differences in temperature and density
Eureka Convection 2:06

17. Convection –.

18. Convection currents are set in motion by –
Heating and cooling of a fluid
Changes in the density of the fluid
Force of gravity

22. 2 1 3

23. 3 2 1 1

24. Convection Currents in the Earth
Happen in the mantle Caused by heat from the core and the mantle Rock in lower mantle is hotter and less dense than rock in upper mantle . Hot rock rises Cools at top mantle sinks back Heats up and rises again

26. Methods of heat transfer -
Convection in the earth –

27. Continental Drift C4S3
Wegener's hypothesis was that all the continents were once joined together in a single landmass - Pangaea - and have since drifted apart.
Alfred Wegener
Pangaea – the super continent

29. Evidence of Continental Drift
Evidence from Land Features
1. Continents fit together like the pieces to a puzzle
2. Mountain ranges on Africa and South America line up
3. European coal fields line up with North American coal fields.

30. 2. Fossil evidence of dinosaurs and prehistoric plants – Glossopteris, Mesosaurus, Lystrosaurus

31. 3. Ancient Climatic Zones – fossils and rocks
Spitsbergen – an island in the Arctic Ocean - once had a warm climate – tropical plants found – island was close to the equator about 300 million years ago, then moved
South Africa - rocks and sediments left behind by glaciers. Continental drift had moved South Africa away from South Pole

32. Sea-Floor Spreading C4L4
The longest chain of mountains in the world is the system of mid-ocean ridges – explored with sonar and deep diving vessels (Hess WWII)
Iceland is a part of the mid-ocean ridge that rises above water

33. In sea-floor spreading, the sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

34. At the mid ocean ridge, a crack develops.
Molten material from deep below earth erupts.
As it cools, it forms a strip of solid rock in the center of the ridge.
When more molten material comes out, it pushes this rock outwards.
New strip of rock is formed.
This produces basalt – the rock that forms oceanic crust

35. Sea floor spreading animation –

36. Evidence of Sea-Floor Spreading
Evidence supported the theory of sea-floor spreading: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves.
Molten Material - shape of rocks – only when molten material hardens quickly under water

37. Magnetic Stripes - patterns in rocks -
rocks of ocean floor contains iron
as this rock cools, the iron atoms become magnetized and line up in the direction of the earth’s magnetic poles
When the magnetic polarity of the earth changes, the new strip shows new polarity
When scientists studied rocks on both sides of ridge, they found strips of rocks alternating on each side in the same way

39. 3. Drilling Samples – age of rocks – the youngest rock was at the center of the ridge, the older rocks were farther away. The farther away from the ridge the rocks were taken, the older they were.

40. Subduction
Deep Ocean Trenches – deep under water canyon where ocean floor sinks

41. Ocean floor near a mid-ocean ridge is new and hot – it moves away towards a deep-ocean trench
As it moves away, it cools – becomes more dense.
Gravity pulls this denser, cooler floor down beneath the trench
Ocean floor sinks back into the mantle
Giant conveyor belt – material comes up at the ridge, moves across ocean floor, sinks at trench
Takes tens of millions of years

42. Animation of subduction - http://earthguide. ucsd

43. It takes 200 million years for new rock to form at mid-ocean ridge, move across ocean, and sink into deep-ocean trench Pacific Ocean is shrinking - has many deep ocean trenches at edges of continents - subduction occurs faster than new rock is formed Atlantic Ocean expanding – fewer deep ocean trenches – as ocean floor spreads, pushes continents – has nowhere to go

44. The Theory of Plate Tectonics
Pieces of the lithosphere are in slow, constant motion driven by convection currents in the mantle
It explains the formation, movement, and subduction of Earth's plates (cracks in the lithosphere)
Convection currents in the mantle cause plate motion

49. Plate Boundaries There are three kinds of plate boundaries:
Divergent: spreading boundaries
Convergent: colliding boundaries
Transform: sliding boundaries.

50. Divergent: Spreading Boundaries
Two plates move apart
Can be found at mid ocean ridges where sea floor spreading happens (Ocean floor)
Spreading boundaries on land produce rift valleys example Great Rift Valley -
in East Africa
(deep crack in the African
continent)
Oceanic crust is created

51. https://www. classzone

52. Convergent: colliding boundaries
Two plates come together
Density of the plates decides which one will be on top
Oceanic crust is destroyed
Three types of collision plates

53. Two Oceanic Plates Meet at a trench
The denser plate sinks (subducts) under the other plate (as the ocean floor undergoes sea floor spreading, it becomes cooler and denser)

54. Oceanic Continental Plates
The denser oceanic plate sinks (subducts) beneath the less dense continental plate

55. Two Continental Plates
Two continental plates collide
Neither is more dense so no subduction
Forms mountain ranges (example Himalayas)

57. Transform: sliding boundaries
Two plates slip past each other moving in opposite directions
Crust is neither created nor destroyed