1. Student Presentations Ch. 14 Lesson 2

2. Mapping the Ocean Floor
Mid-Ocean Ridges- Mountain ranges in the middle of the oceans
After WWII scientists explored the seafloor
Topographic maps create of the seafloor

3. Seafloor Spreading
Seafloor Spreading- The process by which new oeanic crust forms along a mid-oceanic ridge and old oceanic moves away from the ridge
Helped explain continental drift
When the seafloor spreads mantle melts it creates magma
Which rises through along the mid-ocean ridge
Lava erupts into water, it cools rapidly and creates a rock called basalt
As the seafloor spreads apart older oceanic crust moves away from the mid-oceanic ridge
The closer the crust is to the mid-ocean ridge the younger the crust is

4. Topography of the Sea Floor
By Ariel Eskin and Shmuel Metz

5. The rugged mountains that make up the mid-ocean ridge system form in two ways
Large amounts of Lava can erupt from the center of the ridge, than cool and build up around the ridge
The lava can also cool than crack, while the rocks move up or down the cracks in the sea floor, forming mountain ranges

6. Over time sediment accumulates on top of the oceanic crust
Close to the mid-ocean ridge there is almost no sediment
Far from the mid-ocean range, the layer of sediment becomes thick and makes the sea floor smooth

8. Moving Continents Around
By Marc Abelman, Sarah, and Hanna

9. The theory of seafloor spreading is one of the reasons for continental movement. Continents don’t move through the solid mantle or seafloor. But the move when the seafloor spreads along the mid-ocean ridge.

11. Developement of a theory, Magnetic reversals, ROcks reveal magnetic signature
By Neil and Sigal

12. Development of a theory
-Scientists study the magnetic signature of minerals in rock on the seafloor to support the theory of the seafloor spreading
-To understand this you must understand the orientation of Earth’s magnetic field and how rocks record maagnetic information

13. Magnetic Reversals
-The direction of Earth’s magnetic field is not constant
-The normal polarity is a state in which magnetized objects such as compass needles will orient themselves to point north
-Magnetic reversal occurs and the magnetic field reverses direction. This occurs every few hundred thousand/ million years
-reverse polarity is a state in which magnetized objects would reverse direction and orient themselves to point south.

15. Rocks reveal magnetic signature
-When lava erupts from a vent along the mid ocean ridge it cools and crystallizes. this permanently records the direction and orientation of Earth’s magnetic field at the time of the eruption.
-Scientists discovered parallel patterns in the magnetic signature of rocks on either side of the mid ocean ridge

16. Iron rich minerals and cooling lava align with Earth’s magnetic field
Iron rich minerals and cooling lava align with Earth’s magnetic field. When the magnetic field change direction, minerals in fresh lava record a new magnetic signature

18. By: Addi, Avigayil, Chana
WHERE IS YOUR PROOF?
By: Addi, Avigayil, Chana

19. The Science Behind It
Scientists studied magnetic minerals in rocks from the seafloor!
They used a magnetometer to measure and record the magnetic signature of these rocks and revealed parallel magnetic stripes on either side of the midocean ridge!
Each pair of stripes has a similar composition, age, and magnetic character.

20. The stripes represent normal or reversed polarity

21. Drilling
Scientists drilled holes into the seafloor and measured the temperature
beneath the surface.
Scientists measure the amount of thermal energy leaving Earth
Results show that sediment closest to the mid ocean ridge is younger than that farther away.