1. Earth Science Evidence for the SLOW CHANGES we can’t see

2. Continents- Do they REALLY move? RECAPPING: What were the two observations Alfred Wegener made to support his claim of Continental Drift? 1) The continents look like they fit together; and 2) There are fossils found of the same type on opposite sides of the ocean (which nicely line up when you push the continents back together).

3. Continents- Do they REALLY move? RECAPPING: After the undersea mountains (ridges) were discovered, what did Harry Hess notice about them? They have big cracks in them, called rifts. What was happening in the rifts? Lava was slowly pouring out, forming new crust and causing SEAFLOOR SPREADING

4. Continents- Do they REALLY move? RECAPPING: Other support for Hess’ theory: Magnetic particles in the rock, called magnetites were arranging themselves according to changes in the magnetic field of the Earth, changing direction.

5. Continents- Do they REALLY move? And yet more evidence: (write this down) The AGE of the rocks got older the further away from the ridge, and it was perfectly symmetrical on both sides.

6. Continents- Do they REALLY move? Also, by dating the rocks in the sea floor, as well as on the continents, it was discovered that the further away from these ridges, the older the rocks. The oldest seafloor rocks are only about 200 million years old- that sounds OLD!! But not compared to Some rocks on the continents are BILLIONS of years old.

7. So, how do plates move? Notice the upper layer in the mantle- called the ASTHENOSPHERE it’s the liquidy bit. Now notice the crust and the solid bit under it Called the LITHOSPHERE

8. So, how do plates move? Convection currents form in the magna, moving plates above.

9. Some spreading starts on land Large continents begin to crack and split apart The gaps fill with water Small seas become oceans The mid ocean ridge continues to produce new crust

10. It happened with the Red Sea. It’s getting wider, just like Iceland!