1. The Seafloor

2. Types of Crust Two types of crust 1. oceanic 2. continental
Deepest part of ocean is Marianas Trench in Pacific Ocean (just over 11 km deep!)

3. Continental Crust
Continental crust is land that we live on and can see

4. Oceanic Crust
Oceanic crust is covered by water

5. Ocean Floor Topography
Maps show underwater ridges have deep-sea trenches near them

6. Mid-Ocean Ridges Most common features of the ocean basins
Mid-ocean ridges often have volcanic eruptions and earthquake activity

7. Mid-Ocean Ridges of the World

8. Seafloor Spreading
Henry Hess explained data collected
Seafloor spreading theory – new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches

9. Seafloor Spreading
Magma is less dense than surrounding rocks. It is forced upwards towards the crust along an ocean ridge and fills the gap that is created. When magma hardens, a small amount of new ocean floor is added to Earth’s surface. The sections of ocean floor slowly move away from the ridge.