The mechanism for continental drift

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Presentation transcript:

The mechanism for continental drift Sea-Floor Spreading The mechanism for continental drift

Theory of Continental Drift Remember Wegner proposed that over time, continents drift apart? Well how did this happen?

Mid-ocean Ridges SEA-FLOOR SPREADING Scientist (Harry Hess) noticed that there are mountain ranges that exist under water in the Oceans Ex: Mid-Atlantic Ridge These mid-ocean ridges exist due to SEA-FLOOR SPREADING

Sea Floor Spreading Video The process by which new oceanic lithosphere is created as older materials are pulled away. As tectonic plates move away from each other the sea floor spreads apart and magma rises to fill in the gap. Sea Floor Spreading Video

Sea-Floor Spreading Explained

Sea-Floor Spreading Sea-floor spreading creates new oceanic crust Newer crust is found at the center or near the ridge Older crust is found further away from the ridge (because it is being pushed away from the center of the ridge by new rising magma)

Magnetic Reversals Strongest evidence for sea-floor spreading: Magnetic Reversals recorded in ocean floor Magnetic reversals: The switching of Earth’s north and south pole over time

Magnetic Reversals and the Sea Floor Magnetic minerals found in the magma that bubbles up at the ridge align with the Earth’s magnetic field. Once the molten rock cools, it’s like tiny compasses set in stone This record is carried slowly away from the center of the ridge, forming bands of alternating magnetic reversals Every time there was a magnetic reversal, a new band was formed

Magnetic Reversals Why would Magnetic Reversal bands be evidence of sea-floor spreading? These bands show that different parts (bands) of the crust were formed over different time periods Because with each band, the rock patterns that form that part of the crust are different from the other bands nearby

Magnetic Reversals

Magnetic Reversals