The Theory of Continental Drift

1
The Theory of Continental Drift
2
Continental Drift Theory(1910)

• Alfred Wegener was the first scientist to
  hypothesize that the continents had moved from
  their original locations.
• He hypothesized that the continents had once been
  joined together in a single land mass and have
  since drifted apart.
• He named this supercontinent Pangaea.

3
Continental Drift Theory(1910)

• Over tens of millions of years, Pangaea began to
  break apart and move.
• The idea that the continents slowly move over the
  Earths surface became known as continental drift.

4
Alfred Wegener (German Scientist)

• This picture was taken around 1925 (5 years
  before he died)

5
Evidence to Support the Theory
6
Evidence to Support the Theory

• A.) Landforms- Mountain ranges and coal fields
  from different continents matched up with other
  continents.
• B.) Fossils- Fossils of creatures/plants that
  couldnt swim/travel long distances were found on
  different continents that were seperated by large
  bodies of water (Glossoteris (ferns) in
  Antartica, Mesoaurus (reptiles) in Africa South
  America.

7
Puzzle Pieces

• Continents look like they could be part of a
  giant jigsaw puzzle.

8
Evidence to Support the Theory

• C.) Climate-Tropical plant fossils were found in
  areas that the climate wouldnt support.
• Wegener could not identify the cause of
  continental drift, so most scientist rejected his
  theory/idea. (How they moved?)

9
Distribution of Fossils

• Plant and animal fossils found on the coastlines
  of different continents.

10
Sequence of Rocks

• Same rock patterns found in South America, India,
  Africa, Antarctica and Australia

11
Problems With The Theory

• No mechanism for movement of continents
• Wind and currents could possibly move fossils
• Theory was not accepted by scientists

12
Sea -Floor Spreading (1960)
HARRY HESS-Scientist who discovered Sea-Floor
Spreading

• Years after Wegener, another scientist suggested
  that the ocean floors moved, thus carrying the
  continents with them.
•  This movement begins at the mid-ocean ridge.
• Here molten material rises from the mantle and
  erupts. The molten material then spreads out,
  pushing
• older rock to both sides of the ridge.
• This process of continually adding new material
  to the ocean floor is called subduction.

13
How can the ocean floor keep getting wider and
wider?????

• Instead of the ocean getting wider, parts of the
  ocean floor plunge into deep-ocean trenches and
  subduction takes place.

14
Subduction

• Subduction- the process by which the ocean floor
  sinks beneath a deep-ocean trench and back into
  the mantle. Convection currents under the
  lithosphere push new crust that forms at the
  mid-ocean ridge away from the ridge and toward a
  deep-ocean trench.