EARTH 20 Lecture Notes - Lecture 5: Seafloor Spreading, Plate Tectonics, Oceanic Crust
Document Summary
Seafloor is no older than 200 million years old. Continental drift requires oceanic basins to open up, spilling out new crust: Spreading at mid-ocean ridges can explain ridge-parallel stripe patterns. Age determined through seafloor drilling (very expensive) Evidence: appalachian mountains (north america) and scottish highlands (united kingdom) have identical geological features. Reconstruction of pangea and recent continental drift clears up: Fossil data difficult to explain with permanently separated continents. Remains of mesosaurus (freshwater reptile) found in brazil and africa. Plant fossil found in argentina and s. africa. Glossopteris fossils found in all southern continents. Lystrosaurus (land reptile) found in africa, antarctica and india. Evidence of glaciation (land masses being covered by glaciers or ice sheets) on several continents. Ice flow direction can be determined based on scratch marks in ice. All glaciers (when laid out in predicted previous pattern) showed scratch marks facing towards north (??) Movement of plates responsible for present shapes and location of continents.
