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10.1 Continental Drift Continental Drift 10.1 Continental Drift Wegener's Hypothesis · proposed by Alfred Wegener in 1912 · hypothesized that all continents were once a supercontinent called Pangea began breaking apart 250 million years ago continents drifted to their current locations Evidence for Continental Drift 1. Jigsaw Puzzle continental shorelines fit together like puzzle pieces 2. Fossils matching fossils found on different landmasses, but could not have crossed the oceans ex. Mesosaurus 3. Rock type and structure mountain chains on the coastline of one continent continue on continents across the ocean ex. Appalachian Mtns. Click for Video Missing Evidence · Wegener could not provide an acceptable mechanism for the movement of the continents · Wegener's hypothesis declined · proof came a few decades later when scientists discovered sea floor spreading Mesosaurus 4. Ancient climates ancient glaciers in warm climates or tropical species in Antarctica Mid-Ocean Ridges · undersea mountain ranges with a crack, or rift, in the center through which magma rises · sediment closer to the ridge is younger than sediment farther from the ridge · oldest oceanic rock = about 175 million years old Sea-Floor spreading · proposed by Harry Hess · named by Robert Dietz · process by which new ocean lithosphere (sea floor) is formed as magma rises to Earth's surface and solidifies at a mid-ocean ridge Click for video 10.1 Continental Drift Review: Earth's Magnetic Field · the movement of Earth's liquid iron core produces a magnetic field around Earth · compass needle points to the geomagnetic North Pole Geomagnetic Reversal Time Scale · normal polarity - rock's magnetic field points north · reversed polarity - rock's magnetic field points south · alternating patter of normal and reversed polarity when rocks are placed in chronological order Review Questions 1. Who proposed the idea of continental drift? 2. List the 4 pieces of evidence supporting CD. 3. Why was CD declined? 4. Who proposed the theory of sea-floor spreading? 5. What is sea-floor spreading? 6. What evidence(s) supports sea-floor spreading? Paleomagnetism · residual magnetism in rocks · as magma cools on the sea floor, iron-rich minerals align with Earth's magnetic field · magnetic orientation (direction) become permanent when rock hardens Magnetic Symmetry · magnetic patterns on each side of a mid-ocean ridge are symmetrical · allows scientists to date rocks · discovered that new rocks form at the center of a ridge and move away in opposite directions · provided proof for Hess's sea-floor spreading idea and Wegener's continental drift hypothesis