"Wegener's Continental Drift Hypothesis"
Wegener’s Continental Drift Hypothesis The continents fit together like a puzzle Fossil Evidence •Evidence of organisms on continents separated by large oceans, these organisms could not swim across the oceans Geologic Evidence •Mountain ranges of similar rock types and structure that extend from one continent Climate Evidence Glacial evidence in areas that are now tropical indicate continents were once located in southern regions Wegener’s Biggest Problem. Explaining HOW the continents move. Plate tectonic theory states that the earth’s outer shell consists of individual plates that move and interact with each other Plate Tectonic Theory Advances in technology provided evidence that plates are moving and led Geologist Harry Hess to develop the idea of: Sea floor spreading- new crust is being created at mid-ocean ridges and recycled at trenches. Plate Tectonic Theory Evidence 1. SONAR Sonar means SOund NAvigation Ranging During WWII, SONAR was used to detect enemy submarines. Soundings done over the years. Geologists analyzed the sonar data from WWII and… …discovered ridges (mountains) and trenches (deepest parts of the ocean) on the ocean floor. These features are directly related to sea floor spreading and plate movement Sonar proved that the ocean floor was not flat: Later technological advances showed that these features are related to ocean floor recycling. Example: Pacific Ocean is getting smaller at trenches Atlantic Ocean is getting bigger at ridges 2. Magnetometers Magnetometers were used during WWII to detect enemy submarines. Scientists already knew about Earth’s Magnetic Field They also knew that when Fe- rich rocks cool the atoms align in the direction of earth’s magnetic Iron field. Iron atoms in atoms in magma rock In the 1960’s it was discovered that throughout earth’s history there have been periods of normal polarity and reverse polarity. A record of these reversals was recorded as the new material along a ridge solidified into rock on the ocean floor 1960’s: Geologists analyzed the magnetometer data from WWII... …and it revealed a symmetrical pattern of stripes on each side of the ridge representing the record of Earth’s magnetic reversals. As new material is being formed at the ridge, the direction of the magnetic field is recorded as the magma hardens: The magnetometer evidence: • The data showed that the magnetic fields were parallel to the ridge and a mirror image across the ridge • This supports the theory that new material is being formed at the ridge and the magnetic field direction is being recorded over time as the magma hardens in to rock 3. Radiometric dating: Scientists collected samples of the ocean floor crust across the Atlantic Ocean to determine the age of these rocks The Glomar Challenger It was found that the oldest rocks are located farthest from the ridge…. and the youngest rocks are located near the ridge…. Radiometric dating • The age of the rocks across the ridge supports sea floor spreading and plate tectonics by verifying that the youngest rocks are nearest the ridge and the oldest rocks are furthest from the ridge 4. GPS- Global Positioning System • The system uses satellites to provide precise locations of ground receivers all over the globe • GPS provided the first direct evidence that continents actually move We’ll plot GPS data on our plate maps at the end of this unit…….