1. QUICK REVIEW… Layers of the Earth
Crust (2 types)
Mantle
Outer Core
Inner Core
Earth’s crust & the very top solid portion of the mantle form the lithosphere
The lithosphere sits on top of the liquid asthenosphere

2. LAW OF UNIFORMITARIANISM
Law of Uniformitarianism: States that Earth is an always changing place
The same forces of change are at work today that were at work in the past.
Some changes are gradual; some changes are fast…some times both!

3. TECTONIC PLATES
The Lithosphere is broken into many large and small slabs of rock called tectonic plates and where two plates meet, a lot of changes can occur.

4. How do the tectonic plates move?
The plates move because of convection currents.
The hot, soft rock in the mantle rises…then it cools, and sinks.
How do the tectonic plates move?

5. There are 3 types of plate boundaries
TECTONIC PLATES
1. Divergent
2. Convergent
3. Transform
There are 3 types of plate boundaries

6. SUBDUCTION What is SUBduction?
When one tectonic plate sinks under another plate
IT CAN ONLY HAPPEN WHEN…
Continental & oceanic plate collide = oceanic plate ALWAYS sinks because it is more DENSE.
Oceanic & oceanic plate collide = the more dense plate sinks!
What is SUBduction?

7. DIVERGENT

8. DIVERGENT Mid-ocean Ridges Rift Valleys Earthquakes Volcanoes
What occurs at this boundary?
New Crust Forms
Mid-ocean Ridges
Rift Valleys
Earthquakes
Volcanoes

9. CONVERGENT: CONTINENTAL-CONTINENTAL

10. CONVERGENT: CONTINENTAL-CONTINENTAL
What occurs at
this boundary?
High mountains
Earthquakes

11. CONVERGENT: OCEANIC-OCEANIC

12. CONVERGENT: OCEANIC-OCEANIC
What occurs at this boundary?
Deep-ocean Trenches
Volcanic Islands
Earthquakes
Hawaii is NOT on a plate boundary!

13. CONVERGENT: OCEANIC- CONTINENTAL

14. CONVERGENT: OCEANIC-CONTINENTAL
What occurs at this boundary?
Deep-ocean trenches
Coastal mountains (some are volcanic)
Earthquakes

15. TRANSFORM

16. TRANSFORM
What occurs at this boundary?
Faults
Earthquakes

17. PANGAEA
Scientist Alfred Wegener noticed that Earth’s continents seemed to fit together like a puzzle, so he hypothesized that they were once joined in a single “super continent” called Pangaea which means “all land”

18. CONTINENTAL DRIFT
This led to his Theory of Continental Drift – that although the continents were once joined, they slowly drifted apart!
But nobody believed him …why?
Wegener’s Evidence:
1. Matching rock layers on different continents
2. Matching fossils on different continents
3. Evidence of climate change – tropical plant fossils in cold places, ice scratches in warm places

19. SEA FLOOR SPREADING
The sea floor spreads apart at divergent boundaries allowing new crust to form…this new crust builds Mid-Ocean ridges
The crust closest to the crack is the youngest while the crust further from the crack is older

20. MAGNETIC REVERSALS
Minerals in the magma that rise through the cracks in the sea floor align themselves with Earth’s magnetic poles (North and South)
As the rock cools, the minerals stay fixed in this position, like a compass
Earth’s poles periodically reverse. The “stripes” of rock along the ocean floor record these reversals.