It’s all about … CONVECTION CURRENTS!!!!!!

7.2 Drifting Continents Objectives: What is continental drift? How do landforms, fossils, and climate changes show evidence of the changing surface of the Earth? Explain how sea-floor spreading provides a way for continents to move.

Tech Terms: Alfred Wegener – German scientist whom in the 1900’s hypothesized that the continents had once been a huge landmass which he called Pangaea (“all lands”).

Let’s fit the pieces of Wegener’s puzzle together! Independently, use the old book p. 118-122 Complete Chart & Illustrate!

continental drift – the slow movement of continents over Earth’s surface. It was a hypothesis, that was tested. Why did he believe in this theory? fossil – any trace of an ancient organism that has been preserved in sedimentary rock.

Wegener used evidence from landforms, fossils, and climate to support his hypothesis. Wegener’s hypothesis was rejected because he could not provide an explanation for the force that pushes and pulls the continents. Where is the math? How can you recreate this experiment?

PBS Videos: Why Wegner began his hypothesis! Alfred Wegner and his hypothesis in review:

Let’s Review together: (2nd chart) Define and illustrate the following 3 terms: Old book p. 118-122. Pangea Wegener Disbelief

New Evidence to support his claims? Cooling & Shrinking Sea Floor Spreading Molten Material and Magnetic Stripes Convection Currents

Wegner’s Further Evidence: http://www.pbslearningmedia.org/resource/ess05.sci.ess.earthsys.wegener2/plate-tectonics-further-evidence/

7.3 Sea Floor-Spreading 1. mid-ocean ridge – longest chain of mountains extending into all of Earth’s oceans, that curves like the seam of a baseball along the sea floor.

2. sea floor spreading – the process that adds new material to the ocean floor at the mid-ocean ridge. Molten material erupts and spreads out through the valley that runs along the center of the mid-ocean ridge. It then pushes aside the rock that was already there.

It’s all about … CONVECTION CURRENTS!!!!!! Sea Floor Spreading: Continental Drift inside the mantle (2 min)

Sea-floor spreading is the process by which _________ ____________________ forms as magma rises toward the surface and solidifies. As the tectonic plates move away from each other, the sea floor spreads apart and magma fills in the gap. NEW Oceanic Lithosphere

deep ocean trench – this forms from subduction Subduction- (the oceanic crust bends downward forming a deep underwater canyon on the ocean floor).

deep ocean trench examples

4. subduction – Part 2: when the ocean floor sinks beneath a deep ocean trench and gets swallowed by the mantle.

Alaska

Sea-floor spreading and subduction can change the size and shape of the oceans. The Pacific Ocean, aka The Ring of Fire, has lots of subduction zones, thus it is getting smaller. The Atlantic Ocean is expanding!

NEW Evidence of CD And Sea-Floor Spreading? Magnetic reversals in oceanic crust are shown as bands of light blue and dark blue oceanic crust. Light blue bands indicate normal polarity, and dark blue bands indicate reverse polarity

So what will happen as these plates in the ocean floor continue to spread? Earth 100 Million Years from now Convection Currents in the Earth. One more time, a different way! Plate tectonics on a cocoa earth - YouTube