Our Our Changing Changing EarthEarth

What is a Theory?What is a Theory?

• In science, it’s almost the same as a fact

• Must be some sort of evidence to support a theory

• Even with evidence there is still debate about how true it is

Continental Drift TheoryContinental Drift Theory• Alfred Wegener said the world used to be one

large land mass millions of years ago• The land was called Pangaea • Pangaea kept moving apart a few centimeters

each year• After millions of years it became the world we

see today

Continental Drift TheoryContinental Drift TheoryEvidence for

Continental Driftincludes includes

includes includes

Continental Edges

Same Fossils Climate

Rock Structures

Puzzle PiecesOn different continents

Continental ice sheets

Mountains with similar

features

fit like

found seen in evidence from

showed

Plate TectonicsPlate Tectonics

• Plate Tectonics – a more advanced theory about how the continents move

• Explains that there are loose plates in the earth that shift causing:– Oceanic Trenches – Mountains– Volcanoes – Earthquakes.

How Do the Plates Move?How Do the Plates Move?

http://library.thinkquest.org/17457/english.html

So…So…

• Continental Drift – theory that says continents drift around on plates

• Plate Tectonics – theory that explains WHY scientists believe the continental drift theory is true

Now it’s time for a…Now it’s time for a…

What is Continental Drift?What is Continental Drift?

Theory that says the continents are moving on plates

What is Plate Tectonics?What is Plate Tectonics?

Theory that explains WHY scientists think continental drift

occurs

It tells us how the earth’s plates move

Divergent BoundariesDivergent Boundaries

• This is when the plates move apart

• It happens mostly between oceanic plates

• The rising magma causes volcanoes and underwater mountains to be formed

Convergent BoundaryConvergent Boundary

• When the two plates are in the OCEAN they collide and form deep trenches.

• When the two plates are on the CONTINENTS they collide to form mountains.

Transform (Sliding) BoundariesTransform (Sliding) Boundaries

• This is when the plates slide past each other or move horizontally

• The sliding is what causes earthquakes

• This type of boundary is found in California