Explaining the patterns with a model Geologists had no good way to explain these patterns until the middle of the 20th century. Then Harry Hess promoted the idea of seafloor spreading. Let’s do a little reading • Read the Sea Floor Spreading handout. • What patterns that we have seen so far can be explained using this model? Remember, you are just operating from what you read, not your prior knowledge. Let’s figure out how plates interact • Put your hands (plates) horizontally out in front of you, with your thumbs touching. • Pull your hands apart sideways. What should call call it when plates move this way? • On Earth, would there just be a giant hole between the plates? • Now push your hands together. What do the plates do? • What should we call this motion? • Last one – hold one hand still and slide the other one directly away from you. • What should we call this motion? So these were our three kinds of motion: • Divergent plate boundary – plates pull apart & something fills in the gap. • Convergent plate boundary – plates move toward each other and one plate overrides another • Transform boundary – two plates slide past each other horizontally. • Dance! Let’s read a bit • Read p. 201, Divergent Boundaries ONLY • Now think about all the patterns we have seen so far. Does the divergent boundary model help us explain any of them? Time to reason • We’ll use the Give One, Get One protocol • Make this chart: My partner’s ideas… My ideas… Mercury Venus Earth Now for some ideas In the row of your chart for your ideas, write 3 answers to this question: What evidence have we seen that supports the idea that divergent boundaries exist? Now go collect some other ideas • • • • • • In a minute you will go find your first partner. Listen while your partner tells you their idea. Paraphrase the idea back to them. Write it down. Tell your partner your idea while they listen. Listen to the paraphrase. Then they write down your idea. • Wait until you are told to find your next partner. Let’s pool our thinking • On a share sheet, we’ll record all the evidence we have seen so far that divergent boundaries exist. Another reading interlude. • Read the paragraphs about Transform boundaries on p. 201. • What data patterns can we explain using the transform boundary model? Recycling idea • Let’s go back to Harry Hess & his model of spreading and notice this statement: • “Harry Hess did not believe that the Earth was getting any larger so, just as new seafloor is created at the mid-ocean ridges, older seafloor must be returned to the Earth’s interior somewhere.” How is the recycling happening? • Think about our original data patterns. • Now let’s read about Convergent Boundaries. • Which of our data patterns can we explain using the convergent boundary model? The colors on this map are a bit different: • Yellow is closest to the surface • Blue and red are the deepest Imagine we had a giant knife and we cut through Sumatra along the line from A to A’. This is a picture that would show where earthquakes happened in that side view. Applying the model • Now we can ask if there is plate tectonics anywhere else in the Solar System. • We already looked at Mars and the Moon, and they are very different from the Earth. • Now let’s look at Venus • Find your handout on Thinking About Patterns in the Planets • We have mostly topographic data from Venus, so we will use the same chart we used to look at topography on the Earth Your job is to construct with your partner an argument for whether Venus does or does or does not have PT. The structure of an argument is: CLAIM, EXPLANATION, EVIDENCE.