1. Plate Tectonics Current Theory

2. Plate Tectonics  Theory that explains how large pieces of the lithosphere (Plates) move and change shape (Holt 247).  Driving force is convection current in the mantle

3. Evidences

4. Mid-Ocean Ridges  Long undersea mountain chain with narrow valleys and step sides.  Form by “…magma rises from the asthenosphere, and that creates new oceanic lithosphere as tectonic plates move apart” (Holt 242).  Found most earthquakes happened at these ridges

5. Seafloor Spreading Harry Hess and Robert Dietz (1960s)  Crust separates at mid-ocean ridges  New seafloor forms from upwelling of magma into cracks  Seafloor spreads as new magma is brought out

6. Seafloor Spreading Continues J. Tuzo Wilson (1965)  Canadian geologist  Described his idea as rigid “plates,” three boundary types pricellaea52.edublogs.org

7. Paleomagnetism  The recording of the magnetic field in ancient rocks that gives the direction and intensity of Earth’s magnetic poles at the time the rocks formed.  Provided evidence for seafloor spreading  Pattern was symmetric around the ocean ridges

8. Geological  Earthquakes and volcanoes  Most are found along plate boundaries  http://earthquake.usgs.gov/earthquakes/re centeqsww/ http://earthquake.usgs.gov/earthquakes/re centeqsww/  http://www.iris.edu/seismon/bigmap/index. phtml http://www.iris.edu/seismon/bigmap/index. phtml  http://earthquake.usgs.gov/earthquakes/re centeqsus/Maps/US2/40.42.-113.-111.php http://earthquake.usgs.gov/earthquakes/re centeqsus/Maps/US2/40.42.-113.-111.php

10. Fossils