1. Tectonic Plates

2. Layers of Earth
Lithosphere – outer part of the Earth’s crust. Composed of solid rock.
Asthenosphere - the zone below the lithosphere which is more ‘plastic’ so it is easier to bend and move
Radioactivity is the sourc of heat in the mantle

3. 2 Kinds of Crust Continental – less dense, thicker
Oceanic – more dense, thinner

4. 2 Kinds of Mantle Upper – solid, floats on…
Lower – plastic (somewhat fluid)
Why?
Earth’s crust and upper mantle “float” on the plastic portion of the mantle. (asthenosphere)

5. Convection Currents Movement of hot liquid or gas Heated – rises
Cools – drops
Earth’s Crust Cracks…
Convection currents in mantle cause cracking in crust
Thermal Convection cause seafloor to spread and continents to drift

6. Convergent Boundary
Divergent Boundary

7. Divergent – Ocean to Ocean
New crust formed and pushed up - Mid Oceanic Ridges
Ex. Mid-Atlantic Ridge
Ocean Ridges

8. Divergent- Continent to Continent
Continent spreads, ocean basin may form
Paleontologist noticed that fossils were on different continents
Arthur Holmes – First proposed that thermal convection in the mantle causes continental drift
Ex. Red Sea

9. Convergent – Ocean to Ocean
Older slips below newer
Subducted plate melts
Volcanic islands formed
Ex. Aleutian islands, Japan

10. Convergent – Ocean to Continent
Ocean plate goes below continent
Subduction
Subducted plate partially melts
Trenches – the deepest parts of the ocean.
Volcanic mountains
Ex. Western South America

11. Aleutian Islands
Islands of Japan

12. Convergent – Continent to Continent
Same densities, no subduction
Compression, folding, uplifting
Ex. Himalayas, Alps

13. Another type of plate movement…
Transform faulting:
Plates move past each other
San Andreas Fault

14. How do you think scientists identified the plate boundaries?
What is the “Ring of Fire?”

15. Crustal Plates “Connect the dots” – volcanoes and earthquakes
8 major plates

16. Pangea Theory 1912 – Alfred Wegener
Idea that continents were once part of one large land mass – theory of continental drift
How did he know?
Continents’ shapes fit together like a puzzle
Rocks and fossils found on different continents matched

17. Early 1960s
Scientific evidence proves continental drift, plate tectonics, and Pangea theory

18. Ocean Features Picture 2