4.1 & 4.2 Plate Tectonics
As explorers began bringing back information
about the world, map makers began to notice
the coastlines of continents could possibly be
matched up……
• Where the continents once touching????
• This led to the formation of a hypothesis.
Continental Drift
• Hypothesis that continents had moved.
– Pangaea: single landmass
– Panthalassa: all seas
Evidence for Continental Drift
1) Fossils of plants and animals in areas that would
have been joined in Pangaea
2) Similar age and types of rocks
•
South America (Brazil) and Africa
Evidence of Continental Drift
3) Sea floor Spreading
•
Mid Ocean Ridges
4) Paleomagnetism
3) Seafloor spreading
• Newest rock is found at mid ocean ridges
• The mid ocean ridges are breaks where
magma flows up from with in the earth
forming new rock.
• Ocean floor is moving away from these rifts
Journal: Seafloor spreading
• Where is the newest (youngest) oceanic rock
found in the diagram?
• Where is the oldest oceanic rock found in the
diagram?
A
B
C
Journal
• In your own words, describe seafloor
spreading:
4) Paleomagnetism
• As magma solidifies, the iron in it aligns with
earth’s magnetic field.
• As earth’s poles switched, the iron bands
polarity switched as well.
• There is a pattern on each
side of a mid ocean ridge which
shows that the sides where
formed at the same time and
then spread out!
The Theory of Plate Tectonics
• Describes continental movement and
proposes an explanation
– 2 types of Crust Oceanic & Continental which
make up the lithosphere
– Below the lithosphere is the asthenosphere which
had the ability to flow.
The Theory of Plate Tectonics
• The pieces of lithosphere float on top of the
asthenosphere
What causes plate motion???
• Convection Currents: warm material rising,
cool material sinking
– Based on density differences
– Less dense materials rise (warm magma)
– More dense materials sink (cool magma)
What causes plate motion???
In plate tectonics,
- cycle of warm magma rising up to the
lithosphere where it cools and solidifies
- The new lithosphere moves away from the
mid ocean ridges
- It cools and becomes more dense
- It eventually is subducted into the
asthenosphere
3 main types of Plate Boundaries
• Divergent
• Convergent
• Transform/ Transverse
Journal
– What does the word diverge mean?
– What does the word converge mean?
Journal: Boundaries
Divergent
Convergent
Transform/
Transverse
Divergent Boundaries
• Two plates moving away from each other
• Forms:
– Rift Valley (Continental/Continental)
– Mid Ocean Ridges (Oceanic/Oceanic)
Convergent Boundaries
• The direct collision of two plates
– Oceanic-Continental
• Form subduction zones and volcanoes
– Continental-Continental
• Form mountains
– Oceanic-Oceanic
• Form Island arcs
Transform/Transverse Boundaries
• When two plates move past each other
– Form Faults
– Can you name a famous local fault???
Microplate Terranes
• Continents are a patchwork of terranes
• Terranes: pieces of lithosphere
– Own geological history
– Separated by faults at its boundaries
– Own magnetic properties
On a separate piece of paper….
Quiz yourself:
1. Name and describe the 3 types of plate
boundaries.
2. At what type of boundary would island arcs
be found?
3. What is the evidence for continental drift?