1. Earth Composition, Continental Drift and Plate Tectonics

2. Structure of the Earth
Inner Core – The center of the Earth. Made of solid iron and nickel.
Outer Core – Liquid iron, gives earth its magnetic field.

3. Structure of the Earth cont’d
Mantle – The largest portion of the Earth, made of dense rock.  x
Asthenosphere – The upper most region of the mantle.
Rock in this layer is semi- melted and can flow. This
is called plasticity. The crust “floats” on this layer.

4. Structure of the Earth cont’d
Lithosphere – The solid outer region of the Earth. The lithosphere is comprised of the crust and a solid region of the upper mantle.

5. Structure of the Earth cont’d
Crust – The “outer skin” of the earth. Two kinds of crust: Oceanic Crust – Only 3-6 miles thick, its dense rocks make up the entire ocean basins. Continental Crust – miles thick, it is made of less dense rock. Pieces - The crust is made up of 12 major interlocking plates.

7. How do we know what the Earth’s interior is like?
Earthquake waves change speed or direction, or are absorbed by different layers.

8. Plate Tectonics – The study of the formation and movement of Earth’s crustal plates.
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9. Evidence for plate tectonics:
The continents look like they
“fit together” like pieces of a puzzle.  
Once good maps were made in the1700’s, it was noted that Africa and South America looked like they fit together.

10. More evidence for plate tectonics:
Fossil Evidence: Fossils of the same type and age found on different, once connected continents.

11. More evidence for plate tectonics:
Matching Rock Types: Rocks of the same type and age on different continents.

12. More evidence for plate tectonics:
Earthquake / Volcano Locations: The positions of earthquakes and volcanoes mark the plate boundaries. E

13. More evidence for plate tectonics:
Mid-Ocean Ridges: Paleomagnetism – Rocks on opposite sides of mid-ocean ridges have similar age and magnetic polarity.

14. What drives plate tectonics?
Convection currents (heat transfer) from Earth’s core which is heated by radioactive decay causes the mantle to circulate, which moves the crust.