Lithosphere—the outermost 100–150 km of Earth Behaves rigidly, as a nonflowing material Composed of two components: crust and upper mantle This is the material that makes up tectonic plates. o Asthenosphere—upper mantle below the lithosphere Shallow under oceanic lithosphere; deeper under continental Flows as a soft solid.
Plate Tectonics o The scientific revolution began in 1960. Harry Hess (Princeton) proposed sea-floor spreading. As continents drift apart, new ocean floor forms between. Continents converge when ocean floor sinks into the interior. o By 1968, a complete model had been developed. Continental drift, sea-floor spreading, and subduction. Earth’s lithosphere is broken into ~20 plates that interact o Glacial Evidence Evidence of Late Paleozoic glaciers found on five continents. Some of this evidence is now far from the poles. These glaciers could not be explained unless the continents had moved. o Paleoclimatic Evidence Placing Pangaea over the Late Paleozoic South Pole: Wegener predicted rocks defining Pangea climate belts. Tropical coals Tropical reefs Subtropical deserts Subtropical evaporites o Fossil evidence Identical fossils found on widely separated land masses. Mesosaurus —a freshwater reptile Fig. 2.10 America Europe
Glossopteris —a subpolar plant with heavy seeds Earth’s magnetic field o Flow in the liquid outer core creates the magnetic field It is similar to the field produced by a bar magnet The magnetic pole is tilted ~11.5 (moires) from the axis of rotation o The magnetic pole intersects Earth’s surface just like the geographic pole does.
- Fall '09
- Plate Tectonics, upper mantle, Felsic