Transcript tectonic plates

The Theory of
Plate Tectonics
What are tectonic plates?
What are tectonic plates?

lithosphere- the crust and rigid upper layer of
the mantle, broken up into blocks called
tectonic plates

3 types of tectonic plates (a.k.a. crust)
1) Continental crust = low-density silicate rock
(granite)
2) Oceanic crust = dense, Iron/Mg rich rock
(basalt)
3) A combination of continental and oceanic
Where are tectonic plates found?
The plates are Earth’s shell; but unlike an
eggshell, these pieces are always being
created, destroyed, or moved
How is plate movement explained?

The theory of plate tectonics- How tectonic
plates move around on a plastic layer of the
mantle called the asthenosphere
“Plastic”- like nacho cheese, pudding, or syrup
Where is plate movement happening?
Where is plate movement happening?
Where one plate ends and another plate begins;
cracks in the lithosphere mark plate boundaries
What are the 3 plate boundaries?
There are 3 kinds of boundaries:
Divergent

= spreading
boundaries
Convergent

= colliding
boundaries
Transform
 
= sliding
boundaries
What are mid-ocean ridges?
What are mid-ocean ridges?
Divergent = spreading boundaries
 Mid-ocean ridge- An undersea mountain range
with a rift valley running through the center of it

Hot magma rises to the surface, cools as rock,
and the new crust spreads out
60 foot-wide
boundary
of the N. American
and Eurasian plates
Mid-ocean ridges = rift zones
Rift- cracks in the center of a ridge where magma,
which is less dense than rock, flows upward
Mid-ocean ridges = rift zones
Rifting causes new crust to push the older crust aside;
they are divergent, or spreading, boundaries
What is paleomagnetism?
Iron inside the Earth makes Earth a giant magnet

When hot magma cools off, the bits of iron
in the crust will point to the poles like a
compass needle
Paleomagnetism = Earth’s magnetic memory
Iron in new crust pushes the older crust aside; they
record their polar-charge for thousands of years

The magnetic poles have reversed in the past,
and the rocks on the sea-floor show this change
Proof for the Theory of Plate Tectonics:



Recording movement at plate boundaries (earthquakes)
Studying how magma forms new crust at rift valleys
and mid-ocean ridges (rifting)
Observing that many volcanoes are occurring near
plate boundaries, such as, the Ring of Fire
What is the Ring of Fire?
What is the Ring of Fire?
A zone of active volcanoes and earthquakes that
marks the Pacific Plate boundary
Deep- point that goes very far down into the crust
Trench- steep, narrow valley where a plate ends
For your summary answer…



What are tectonic plates made of?
What are the 3 types of boundaries?
What is paleomagnetism?
Resources
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Wikipedia
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What is the Ring of Fire?
A zone of active volcanoes and earthquakes that
marks the Pacific Plate boundary
Deep- point that goes very far down into the crust
Trench- steep, narrow valley where a plate ends
Warm up
1) Describe one part of this figure
or, describe a part that you do not understand.
2) What do you think is a good title for this figure?
3) How many plate boundaries do you see?