Who was Alfred Wegener? • Alfred Wegener was a young German scientist whoin 1910 proposed that the continents moved. • What was Wegener’s hypothesis?
What was Wegener’s hypothesis? • Continental Drift: all continents were once joined together in a single landmass and have since drifted apart. • What evidence did Wegener have? Pangea means “All lands.”
What evidence did he have? • Wegener gathered evidence from different scientific fields to support his ideas about continental drift. • Wegener studied land features, fossils, and evidence of climate change. Please turn to page 138 -139 of your textbook.
Drifting Continents • Wegener’s idea of a supercontinent was not accepted by the world because he could not provide a satisfactory explanation for the force that pushes or pulls the continents. • What force do you think moves the continents? http://www.livescience.com/images/pangea_animation_03.gif
Who is Arthur Holmes? • Around 1930, Arthur Holmes suggested the power of convection. • Currents of heat and thermal expansion in the Earth's mantle, he suggested, could force the continents toward or away from one another, creating new ocean floor and building mountain ranges. • He warned that his ideas were "purely speculative" and could "have no scientific value until they acquire support from independent evidence."
What is Convection? • Convection is the movement of molecules within fluids. • Movement is caused by differences of temperature and density within a fluid.
1. As a liquid is heated, the particles move faster and spread apart. • 2. As a result, the particles of a heated fluid occupy more space. • 3. The fluid’s density decreases. • THE HOTTER (less dense) LIQUID MOVES UP. • 4. But when a fluid cools, its particles move more slowly and settle together more closely. • 5. As the fluid becomes cooler, its density increases. • THE COOLER (more dense) LIQUID SINKS DOWN. Heat Rises!
So… what possible force can there be that might push or pull the continents? http://www.geoham.net/6/fys/tekton/recon.gif
What force moves the continents? • Heat from the core and the mantle cause convection currents in the mantle. • These currents are believed to be what moves the plates. • Although Holmes had an explanation, he could provide no evidence.