1.2 Continental Drift

Alfred Wegener  

• In 1915 proposed the idea of the continental drift 

  • All the continents were once formed together called Pangia 

  • He puts the idea forth that the same fossils can be found on all different continents 

  • evidence of glaciers/mountain ranges can be found in india, eurasia, south america, and australia  

Idea rejected in 1915? 

• Main problem with Wegner's idea 

  • No suitable mechanism(force) that could move the continents 

1950's and 1960's: seafloor is mapped and drilled 

• Underwater mountain ranges aka mid ocean ridges 

  • After WWII, submarines ran into the mountains allowing them to get a better idea 

• Later the ocean was mapped 

  • High heat flow 

  • Volcanically active 

  • Seismically active 

  • Parallel to margin of continents 

    • Older rocks located further from ridge 

Paleomagnetism 

• Magnetic minerals align themselves parallel to magnetic field while magma cools (1100F) 

• Studies show that continents had drifted over time 

• Compass needle can give idea where continents used to be as the magnetic pull is different in various locations 

  • Flat compass needle: somewhere near the equator 

    • Two strings on both ends of needle, equal weight is being pulled making it level 

  • Steep: rocks were near the poles 

    • One string is being pulled drastically towards the magnetic than the other 

  • Dipped: somewhere near the poles 

    • One string is being pulled more towards the magnetic than the other 

    • The magnetic minerals orientate themselves with the magnetic field as they cool (magma) 

Magnetic reversals 

• Paleomagnetic studies of lava flows showed that Earth's magnetic field periodically reverses itself 

  • Some reason the magnetic pull flip flops going from south to north