1. DRAIN THE OCEANS!

2. Underwater Geologic Features…
If the Earth had no water, there would be massive underwater rock structures exposed that are much bigger than those found on land today.
Examples:
Mid-Ocean Ridges, Deep Ocean Trenches, Volcanos, Thermal Vents

3. How do Scientist know?
Scientist use an instrument called “Sonar” to map out structures that exist on the ocean floor.
Sonar uses sound waves to “see” features.

4. Underwater Features Mid-ocean Ridge
An underwater mountain chain that has magma and lava coming out of it.
As the lava emerges it pushes each side of the sea-floor in opposite directions.
This movement is called sea-floor spreading and is the main cause for the moving of continents as well as earthquakes.

5. Plate Tectonics
The theory that the surface of the Earth is broken into pieces like a puzzle and those pieces are slowly moving.

7. Underwater Features Trench
When two plates crash (collide) one of the plates is “bent” downward creating a deep trench.
The deepest trench in the world is called the Marianas Trench and it is 6.8 miles deep.

10. Underwater Features Volcanos (Hot Spots)
- Single locations on Earth’s surface, mostly on ocean floor, where the crust is thin enough to allow a tube of magma to spit out lava.

12. Hot Spots Create Islands in the Oceans

13. Underwater Features Thermal Vents
- Chimney stacks along the ocean floor that release steamy hot water from geothermal energy beneath the crust.

15. What is the cause for all these features?
Convection of Magma
-Beneath outer layer of Earth (crust) is another layer called the Mantle.
-Within the mantle is hot magma that rises and sinks due to temperature and density differences.
-This magma moves through cracks in the crust to the surface and creates the ocean floor volcanic features.

16. Plate Tectonic Boundaries and Ocean Floor Features
Divergent Boundary (to separate): Mid-ocean Ridges
Convergent Boundary (to collide): Trenches

18. How does density and temperature
effect plate movement?
Hotter material such as material in the earth’s mantle is less dense and rises.
Cooler material in the earth’s mantle is more dense and sinks.
As cooler material becomes hot again it rises
Rising and sinking occurs in a continuous cycle
This circular motion carries plates of the lithosphere along with it the continents move.
This process is called convection currents!