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 Drift1) Fossils of plants and animals in areas that would

have been joined in Pangaea2) 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?