GEOLOGY Notes PART 1 Alfred Wegener (1912) proposed that all the continents were once joined as a single landmass called this “supercontinent” Pangaea called his theory “Continental Drift” stated the continents have separated and collided as they have moved over millions of years Problem= could not explain WHY

Continental Drift

Wegener’s 5 major pieces of Evidence: Continents (esp. South America & Africa) seem to fit together like pieces of a puzzle Matching fossils occur on east coast of S. America & west coast of Africa Matching folded mountain belts on coasts of S. America & Africa

Data for latitudes & longitudes of locations is changing Evidence cont… Evidence of ancient climates show landmasses were once located elsewhere Ex: glaciers in Africa ! Data for latitudes & longitudes of locations is changing

Modern Theory = Plate Tectonics The crust is made up of about a dozen major, moving plates and several smaller plates Plates can contain: land = continental crust ocean = oceanic crust Both !

Modern Evidence from the Oceans Scientists mapping the ocean floor found: Underwater mountain chains Ridges where the sea floor was actually spreading at sites called ridges Some oceans were growing wider from the middle Fossils and other materials are moving apart on either side of ridges Newer, younger crust was being created by magma at the ridges

Magnetic measurements of the crust Modern Evidence cont… Magnetic measurements of the crust Polarity (magnetic north vs. south) changes every so many thousand years Magnetic rocks on the ocean floor show reversals Rocks are in equal bands on either side of the mid-ocean ridges

What Moves the Plates? Convection currents are created as heated rock rises to the surface, cools, and sinks again. These currents carry the plates as if they are on a conveyor belt in a process called “slab pull.”