10.1 Continental Drift

10.1 Continental DriftWegener's Hypothesis

Continental Drift· 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

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1. Jigsaw Puzzlecontinental shorelines fit together like puzzle

pieces2. Fossils

matching fossils found on different landmasses, but could not have crossed the oceans

ex. Mesosaurus3. Rock type and structure

mountain chains on the coastline of one continent continue on continents across the ocean

ex. Appalachian Mtns.4. Ancient climates

ancient glaciers in warm climates or tropical species in Antarctica

Evidence for Continental Drift 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

· 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

Mid-Ocean Ridges 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

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10.1 Continental Drift

· the movement of Earth's liquid iron core produces a magnetic field around Earth· compass needle points to the geomagnetic North Pole

Review: Earth's Magnetic Field 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

· 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

Geomagnetic Reversal Time Scale 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

Review Questions1. 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?