Transcript File
The Theory of Continental Drift Bill Nye https://www.youtube.com/watch?v=rDKiN wTwaNw Sea Floor spreading (already saw but review) https://www.youtube.com/watch?v=GyMLl Lxbfa4 Alfred Wegener A German geologist and meteorologist who first proposed the Theory of Continental Drift in 1912. He used 6 sources of evidence to make his point. However, the scientific community of his time never believed him. Continental Drift: The Theory 200 mya the continents used to all be connected in one giant landmass called Pangaea. The northern half was Laurasia & the southern half was Gondwanaland. The ocean that surrounded Pangaea was called the Panthalassa Sea. The Evidence 1. 2. 3. Continent’s coastlines “fit” together. Mountain ranges on different continents connect. Bedrock on continents “match” with other continents (South America and Africa). Rock Layers Across Continents The Evidence 4. 5. 6. Fossil evidence Glossopteris (an extinct plant) found on nearly every continent. Glacial evidence on different continents connect. Coal deposits (from swamps) found in polar areas. Fossil Tracks Across Continents Glaciation Across Continents Reasons People Doubted Him…. Some say he “modified” coastline data Didn’t explain how continents had moved Other scientists could not figure out what force moved the continents either However, After Wegener’s death in 1930, more clues were found as technology improved Support for Wegener… Support for Wegener came later … thanks to technology advances in the 40’s and 50’s Bathymetric surveys Magnetometers Seismographs Important Discoveries The ruggedness and youth of the ocean floor Repeated reversals of the Earth magnetic field in the geologic past Important Discoveries Proof of the seafloor-spreading hypothesis and recycling of oceanic crust Proof that the world’s earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges Geomagnetic Anomalies The Earth’s magnetic field reverses at random intervals As new rock is formed from magma it records the orientation of the Earth’s magnetic field at the time the magma cools. Geomagnetic Anomalies When studying the sea floor one sees that the “stripes” of magnetized magma is parallel to the mid-oceanic ridge. So finally … His idea is accepted today, only in a slightly different manner we call the Theory of Plate Tectonics