Continental Drift

Note the Shapes South America & Africa: They Match!What about any others? North America?

Continental Drift:

The Idea that the continents move around and change locations on Earth.

Alfred Wegener proposed the idea of Continental Drift

The globe before and after continental separationBy Antonio Snider-Pellegrini, 1858

(pre-Wegener)

“Continental Drift” Evidence: Fossils

“Continental Drift” Evidence: Fossils

• Animal and plant fossils are located on continents that a currently do not touch

• These continents must have touched at some time for matching fossils to be found in the in the areas shown on the continents

“Continental Drift” Evidence: Glacial Markings

• Marks where glaciers used to scrape along the surface are found on continents that must have once touched

• Some of these continents are in areas currently too warm to support glacier devlopment

• These continents must once have been in colder regions

“Continental Drift” Evidence: Glacial Markings

“Continental Drift” Evidence: Mountain Belts

• Mountain belts and rock types connect across continents

• Some matching mountain belts and rock types are found on continents that no longer touch

• These continents must have touched at some time

“Continental Drift” Evidence: Mountain Belts

MovingContinents

…Back in time…

Pangaea

250 million years ago, the continents fit together like a jigsaw puzzle!

●The Continents Move Around on Earth●Evidence for Continental Drift:

Shape of the ContinentsFossils

Glacial MarkingsMountain Belts

●Pangaea existed when all the continents were together

Conclusions

Part 1: The Creation of New Oceanic Crust

Seafloor Spreading

Seafloor Spreading

• Oceanic plates move apart at mid-ocean ridges.

• Magma moves into the rift.• The magma cools and

becomes new ocean floor.• The new material

magnetizes based on the Earth’s magnetic field at the time.

• The new material moves away from the ridge.

• More magma moves into the rift and the cycle continues

Age and Magnetic Field recorded in the seafloor and spread to each side of the ridge

Each side of the

ridge is the same!!

Determining Seafloor Age

●Continents > 4 Billion Years Old●Seafloor < 200 Million Years Old

AGE

continent

ocean

Seafloor Age

AGE

Age distribution• The colors

represent different ages

• The youngest crust is nearest the ridge

• The pattern is symmetric

• The pattern is more obvious in the Atlantic ocean, where spreading has been very even

●The ocean is much younger than the continents.

Continents: 4 Billion yearsOceans: <200 Million years

●Seafloor ages make a mirror image (symmetric) pattern.

Conclusions