Warm Up #10 What is seafloor spreading?

Lesson 2: Development of a Theory Ch. 2 Plate Tectonics Lesson 2: Development of a Theory

Essential Questions What is seafloor spreading? What evidence is used to support seafloor spreading?

Can you guess the age of the glue? ACTIVITY The age of the seafloor can be determined by measuring magnetic patterns in rocks from the bottom of the ocean. How can similar patterns in drying glue be used to show age relationships between rocks exposed on the seafloor? Spread a thin layer of rubber cement on a sheet of paper. Observe for 3 minutes. What patterns do you see? Spread another layer of rubber cement on a sheet of paper. After a minute, what do you notice about the 2 layers? What evidence helped you to determine the oldest and youngest glue layers? How is this similar to a geologist trying to estimate the age of rocks on the seafloor?

Mapping the Ocean Floor Topographic maps of the seafloor showed mountain ranges stretched for many miles deep below the ocean’s surface Mid-ocean ridges – mountain ranges in the middle of the oceans

Seafloor Spreading Seafloor spreading – the process by which new oceanic crust forms along a mid-ocean ridge and older oceanic crust moves away from the ridge Mantle below melts and forms magma Magma is less dense than solid mantle so it rises through cracks in crust along mid-ocean ridge Erupting magma called lava Lava cools and crystallizes on seafloor forming basalt Forms pillow lava due to rapid cooling and forming rounded structures

Warm Up #11 What is normal polarity?

Topography of the Seafloor and Moving Continents Around Forms in 2 different ways: Large amounts of lava can erupt from the center ridge, cool, and build up around the ridge As lava cools and forms new crust, it cracks where rocks move up and down along cracks in seafloor forming jagged mountain ranges We can now answer the question of how continents move: Continents move as the seafloor spreads along a mid-ocean ridge https://www.youtube.com/watch?v=ZzvDlP6xd9o

Magnetic Reversals Normal polarity – a state in which magnetized objects will orient themselves to point north Magnetic reversal – occurs and the magnetic field reversers direction Reversed polarity – a state in which magnetized objects would reverse direction and orient themselves to point south Magnetic reversals occur every few hundreds thousand to every few million years

Magnetic Reversals Why does it go from normal to reversed to normal to reversed and so on? https://www.youtube.com/watch?v=igGsuDYxhEA