J OURNAL #63 1. Describe the process of Sea-Floor Spreading 2. What is Continental Drift 3. What evidence supports continental drift? (Use yesterday’s notes or textbook to help you)

T ODAY, WE WILL REVIEW THE EVIDENCE OF CONTINENTAL DRIFT AND OBSERVE THE CHANGES OF THE CONTINENT ’ S LOCATIONS.

R EVIEW : Wegner developed the hypothesis of Continental Drift The continents once formed a single landmass that broke up and drifted to their present locations Pangaea

E VIDENCE OF C ONTINENTAL D RIFT : The same fossils are found in areas that had once been connected Rocks of the same age and type are found at coastal regions that were once connected. Mountain ranges continue onto continents that are separated by oceans. Evidence of ancient glaciers are found on areas that are currently too warm for glaciers to form.

M ID -O CEAN R IDGES The mid-Atlantic Ridge is part of a system of mid-ocean ridges, which are undersea mountain ranges through the center of narrow valleys. Sediment that covers the sea floor is thinner closer to a ridge that it is father from the ridge. This evidence suggests that sediment has been settling on the sea floor farther from the ridge for a longer time that it has been settling near the ridge. This means rocks closer to the ridge are younger than rocks further from the ridge.

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S EA -F LOOR S PREADING At the center of a ridge there is a crack (rift) in Earth’s crust At this rift, molten rock (or magma) from inside the Earth rises to fill the crack. As the ocean floor moves away from the ridge, rising magma cools an solidifies to form new rock that replaces the ocean floor.

S EA -F LOOR S PREADING As the ocean floor spreads apart at the mid-ocean ridge, magma rises to fill the rift and then cools to form new rock. This process is repeated over millions of years and new sea floor forms. In yesterday’s activity, which sediment layer was the oldest? Which was the youngest?

S EA F LOOR S PREADING A CTIVITY

S EA -F LOOR S PREADING Sea-Floor spreading- the process by which new oceanic lithosphere (sea floor) forms as magma rises to Earth’s surface and solidifies at the ridge. The ocean floor is moving! Therefore continents are probably moving too! Sea Floor Spreading Video

L ET ’ S R EVIEW : The crack in the earth’s crust at the ocean floor is called___? How is new sea floor formed? What do we call this process?

P ALEOMAGNETISM The Earth acts as a giant magnet Use a compass to determine direction Earth has a north and south pole As magma solidifies to form rock,iron-rick minerals in the magma align with the Earth’s magnetic field in the same way a compass needle does. When the rock hardens, the magnetic orientation becomes permanent, called Paleomagnetism

M AGNETIC R EVERSALS Geologic evidence suggest that Earth’s magnetic field has not always pointed north as it does now. Rock show magnetic orientations point opposite the Earth’s magnetic polarities.