Continental Drift:The Beginning of Plate

Tectonics

Theory of Continental Drift

Continental Drift Theory that the continents are

drifting apart and towards each other

Alfred Wegener Idea that all continents were all

pieced together 245 million years ago

Pangaea = “All Earth”

Continental Drift

Argument for and against Continental Drift

Same fossils on different Continents

Rock formations Climate conditions

evidence Glacial grooves on

separated continents

Species could travel over “bridges”

Rock cycle occurs Climate has

cycles Glaciers covered

majority of Earth

Ultimate Question How could gigantic continents

move? What natural force could move

entire continents?

An Answer: Sea Floor Spreading

Process in which new oceanic lithosphere is created as older material is pulled away

Process forces tectonic plates away from each other

Creates mid-ocean ridges which are underwater mountain chains

Sea-Floor Spreading

Evidence for Sea-Floor Spreading

Eruptions of molten material Magnetic strips in the rock of the

ocean floor Ages of rock from drill samples

Magnetic Reversals Earth’s magnetic poles change

place Mineral grains of molten rock align

to the poles of Earth Rocks freeze trapping history of

magnetic reversals

Question: ???? If new crust is being made at mid

ocean ridges and the sea floor is spreading, then why isn’t the Earth’s surface getting larger?

Subduction at Plate Boundaries

Subduction is a process in which the dense ocean floor sinks back into the mantle

Occurs at deep-ocean trenches Convergent boundaries

Quiz: What are the three layers of the

Earth Based on Composition? What are the 5 layers based on Structure?

What is Pangaea? What process showed Continental

Drift is correct?