Restless Continents

1
Restless Continents

• Continental Drift Theory

2
Continental Drift Theory

• Theory that all of the continents were once one
  large landmass (Pangaea) that has broken up and
  drifted apart.
• Alfred Wegener
• Evidence
• Continents fit like pieces of a puzzle
• Fossils of same species animal plants found on
  separate continents
• Glossopteris
• Rock formations
• Matching mountain chains
• Climatic conditions
• Coal fields in Antarctica

3
Breakup of Pangaea

• Pangaea
• Greek for all Earth
• Pangaea broke into two huge continents
• Laurasia
• Gondwana
• These two split again to form the current
  continents

4
Midocean Ridges and Sea-Floor Spreading

• Mid-ocean Ridges
• Underwater mountain chain that runs through the
  Earths oceans.
• Sea-floor spreading
• Process in which new lithosphere forms
• Magma rises to the surface through the mid-ocean
  ridge forming new oceanic crust
• Tectonic plates spread apart and magma fills the
  gap.
• As new crust forms older crust moves away from
  the M.O.R.

5
Evidence of Sea-Floor Spreading

• Crust closer to the mid-ocean ridges is younger
  than crust further away.
• Subduction
• Process in which old ocean floor goes back into
  the mantle through trenches

6
Magnetic Reversals

• Earths north and south poles have changed places
  many times
• Molten rock contains tiny grains of magnetic
  minerals
• These minerals align with the magnetic field of
  the Earth.
• As the magnetic field reverses and new ocean
  floor is formed it leaves a record of this change.