1. Unit 4: How do the oceans change? What are the parts of the oceans?

2. Parts of the Earth The Earth is divided into 3 zones:
Atmosphere: The air above the Earth
Hydrosphere- All the water on the surface of the Earth along with the clouds
Lithosphere- The solid surface of the Earth

4. How does the Lithosphere change?
TECTONICS!

5. Tectonics and the Oceans
The changing of the oceans is due to plate tectonics

7. What is Plate Tectonics?
A theory that states how the Earth’s rigid crust (lithosphere) is divided into approximately 21 plates that can interact with each other through sliding on the asthenosphere
The asthenosphere is part of the upper mantle where the rocks are partially molten and not rigid
These plates are moving carrying the continents and islands with them

9. What is the difference between continents and ocean?

10. Types of Crust Oceanic Crust Continental Crust
Originally formed at mid-ocean ridges
Ranges from 5-10km thick
Predominately consists of Basalt
Density is 2.9g/cm^3
Continental Crust
Average thickness of 35km
Predominately silicate materials (granite)
Density is 2.7 g/cm^3
Which is significantly lower than that of oceanic crust

11. How do you build crust? Magma=Melted Rock
When the rocks hardens it becomes crust
The type of magma, how deep it hardens and how fast it hardens determines what crust it will become!

12. Isostasy
A condition of equilibrium in the lithosphere, where any change in the mass of one part will be off set by a change in the mass of another part
A volcano builds continental crust  Erosion causes continental crust to lose sediment  Crust gets less dense and rises  Sediments are deposited and create a geosyncline  Geosyncline becomes more dense and sinks

13. How do the Plates in the lithosphere move?
Convection Currents
Currents in the mantle are thought to be responsible for the movement of the lithospheric plates
Movement of heat in mantle due to differences in density
Hot magma becomes less dense and rises  Cools and becomes more dense and sinks

15. Evidence Indicating Plate Boundaries
Zones of Volcanic and Earthquake Activity
Ex: West Coast of N. and S. America and the East Coast of Asia
Rift Zones
A valley that forms when rock along a fault is pulled apart, it is found in the middle of the ridge
Ex: Mid-Atlantic Ridge
Fault Zones
Produced as the result of movement of rock along either side of a crack in the Earth’s crust
Ex: San Andreas Fault in California

16. Types of Plate Boundaries Overview

17. Types of Plate Boundaries
1. Divergent Plate Boundary
Where plates move apart
Geologic Features Found Here:
Rift Valley
Volcanoes
Earthquakes
Mountains (Ridge)
Examples:
Mid-Atlantic Ridge
East Pacific Rise

18. Divergent Plates-What’s in the middle?
Rift Valleys (Diverging Boundaries)
A valley that is created where two plates are moving apart from one another
An example of this is the Mid- Ocean Ridge and East African Rift Valley

19. Mid-Atlantic Ridge

20. What happens at the ridge?
SEA FLOOR SPREADING!

21. Sea Floor Spreading Sea Floor Spreading Theory Mid Ocean Ridge
The ocean floors are spreading apart as new rock material is added to the crust in the regions of mid-ocean ridges
Mid Ocean Ridge
Mountain chain running along the middle of an ocean basin
Strip of igneous rock parallel to the ocean ridges shows reversal of magnetic orientation
This provides evidence of sea floor spreading

23. Where’s the Evidence? Age of Igneous Rock on Ocean Floor
The sea floor is younger at the ridges and gets older as you move towards the continents
Reversal of Magnetic Polarity
Igneous rocks at the mid-ocean ridge show magnetic orientation of Earth’s magnetic poles when the rock solidifies

24. Magnetic Polarity Normal Polarity Reverse Polarity
The compass needle would point to north
This is the magnetic orientation of Earth today
Reverse Polarity
The compass needle would point to south
Not today’s magnetic field, but has occurred in the past many times

26. Continental Drift – Seafloor Spreading Connection!!
Alfred Wegener’s missing evidence:
Seafloor spreading explains how the continents move
The continents are on plates, which move over the asthenosphere

28. 2. Convergent Plate Boundary
Where plates move towards each other
Oceanic – Continental
Oceanic – Oceanic
Continental – Continental
Geologic Features and Activities Found Here:
Mountains
On Continents
Volcanoes
Earthquakes
Trench
Deepest part of the ocean
Subduction Zone
Example:
Tonga Trench

29. Subduction Zones
The area where two plates collide together (Converge) and one of the plates (Subducting Plate) is forced down into the mantle where it will be destroyed
Subducting Plate
The plate this is being forced down

31. What forms a subduction zone?
2. Converging Boundaries
Oceanic – Continental
The heavier, more dense, oceanic crust will be forced down (subducted) into the mantle where it will be destroyed
Earthquakes, deep trenches, and volcanic islands are created
An example of this is Japan

32. Oceanic – Continental

33. Example of Japan

34. Deepest Place on Earth https://www.youtube.com/watch?v=ypvNe_oXEXc

35. Continental – Continental OR Oceanic – Oceanic
When two of the same type of plates collides with one another and the more dense of the two is forced down (subducted) into the mantle where it will be destroyed
A lot of earthquake and mountain building occurs at these boundaries
An example of this is India converging with Asia which forms the Himalayan Mountains

36. Oceanic – Oceanic

37. Continental – Continental

38. Himalayan Mountains

39. Why is Everest so tall?

40. Transform (Sliding) Boundaries
Where plates slide past one another
Geologic Activity Found Here:
Earthquakes
Example:
San Andreas Fault

41. San Andreas Fault

43. Hot Spots
Areas of Volcanic Activity in the middle of lithospheric plates
The hot spot does not move!!!
The plates move over the hot spot
Ex: Hawaii
THIS IS NOT A FAULT!!!

44. Ocean Floor Structures

45. How is it all connected?
The movement of tectonic plates creates the shape of the oceans we know today
Different plate boundaries creates different plate structures

46. Mapping the Seafloor Features
Bathymetry – the study and mapping of seafloor elevations.
Techniques
Early explorers measured depth using rope; results were often inaccurate.
Echo Sounder (SONAR) determines depth by measuring the time required for sound to leave a ship, reflect off the sea floor and return to the ship.

47. Mapping the Seafloor Features
Techniques continued
Multibeam sonar systems take several soundings at a time. This is a faster method.
Satellites can measure very large scale sea floor features by determining changes in sea surface elevations.

48. Bathymetry: History and Uses

49. Deep Seafloor Features
Continental Shelf: closest to coastline; nearly flat borders on the edge of the continents that slope toward ocean basins.
Continental Slope – steep slope extending to the seafloor.
Continental Rise – gentle slop formed at the base of the slope due to accumulation of eroded sediments.

50. Abyssal Plain – vast plain extending seaward from the base of the continental slope
Oceanic Ridge – underwater mountain range typically having a valley (rift) running along its spine.
Rift Valley – valley formed from the spreading apart of seafloor at oceanic ridges

52. How does heat near the rift affect elevation?
Heat Flow
A measurement of the amount of heat leaving the rocks of the lithosphere
Heat Flow values are high in the areas of rift where magma is rising
Heat Flow values decrease as you move away from the rift
The elevation at the rift is higher because the rocks expand due to high temperatures
Elevation decreases as you move away from the rift because rocks cool and contract

53. Guyot – flat topped sea mounts caused by erosion
Seamount – steep sided volcanoes rising abruptly, sometimes piercing the sea surface (island formation).
Guyot – flat topped sea mounts caused by erosion

54. Trench – a long, narrow depression on the ocean floor with relatively steep sides. Deepest part of the ocean.
Tectonic plate boundaries converging; subduction cause mountain ranges.

55. Under water Volcano – a volcano not located on an oceanic ridge.
Islands – body of land surrounded by water.
Can be formed by:
Deposition of sediments
An underwater volcano can rise above sea level.

56. Deep Seafloor Profile