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.