PART 1: The Theory of Continental Drift is a hypothesis that states the continents once formed a large, single landmass called Pangaea.

Evidence for Wegener’s theory includes a puzzle – like fit of the continents, identical rock types, identical fossils, and very similar mountain ranges found on different continents that are separated by a wide ocean.

Alfred Wegener

Part 2: 1. Scientists today use sonar to study the ocean floor. Studying the ocean floor helps scientists better understand what is happening to our Earth.

Scientists discovered the ocean floor’s topography is not flat like they once believed.

2. The continental shelf is the section of the continental crust that extends under the water. 3. The continental slope is the steep incline section of the continental crust. It connects the continental shelf to the abyssal plain. 4. The abyssal plain is a large, flat, almost level of the ocean floor covered with thick sediment.

5. The mid-ocean ridge is a long, underwater mountain chain that forms on the floor of the ocean. 6. The rift valley is a long, narrow crack in the ocean floor in the middle of the mid-ocean ridge.

Mountains and valleys

The rift is in the valley of the mid- ocean ridge (the mountains)

7. Seamounts are individual mountains of volcanic material. 8. Ocean trenches are deep valleys or canyons in the deep ocean floor.

You try it:

Continental Shelf Continental Slope Abyssal Plain Mid-Ocean Ridge Rift Valley Deep-sea Trench Seamount

Sea Floor Spreading

1. Sea-floor spreading is the process by which new oceanic crust forms as magma rises through the rift in the mid ocean ridge and solidifies (hardens) making new crust. This new crust pushes the older, colder, denser crust away from the ridge. This movement of the crust away from the ridge moves the continents with it. Flash Presentation Flash Presentation

2. The subduction zone is the area below the trench that pulls the cooler, old, and more dense crust into the mantle. The process of crust being pulled into the mantle is called subduction. kc4lbhhSRs kc4lbhhSRs

So, the process of sea floor spreading creates new crust, but the process of subduction destroys the older crust. Therefore the overall size of the crust does not change.

Continental Drift/seafloor spreading song! v=Saxh_mGHt1I&list=UUJjstNDk wktHyvUdtcBfb2g&index=3

Part 4: 1. The lithosphere is the solid, outermost rigid layer of the earth. It is made of the crust and the upper part of the mantle.

Tectonic Plates: large, solid pieces of Earth’s surface.

2. The asthenosphere is the soft plastic layer of the mantle that flows very slowly.

3. Pieces of the “cracked” lithosphere (tectonic plates) float on top of the asthenosphere. As they float, they are in constant slow motion due to convection currents in the mantle. The moving of tectonic plates on the asthenosphere is the theory of plate tectonics.

4. Where these plates meet,events such as earthquakes and volcanoes occur. The place where plates meet is known as a plate boundary.

mantle convection cells and continental drift.wmv - YouTube

Notice convection currents in the mantle.