Presentation on theme: "The Theory of Plate Tectonics 6 th Grade. Remember what we learned yesterday about continental drift? Alfred Wegener found a variety of evidence that."— Presentation transcript:
Remember what we learned yesterday about continental drift? Alfred Wegener found a variety of evidence that suggested that the seven continents used to be joined together as one large supercontinent. What was the ONE PART of his theory that he was not able to explain?
Alfred Wegener was not able to explain the force that moved the continents
What force is great enough to move the heavy continents?
Geologists think that the movement of convection currents in the mantle is the major force that causes plate motion!
The Theory of Plate Tectonics: States that pieces of the Earth’s lithosphere called plates are in slow constant motion because of convection currents in the mantle
Remember that the convection currents (heat transfer) that are occurring in the mantle are causing these plates to move
Scientists use instruments on satellites to measure plate movement. Plates move at slow rates: ex. The North American and Eurasian plates are moving apart at 2.5 cm per year –about as fast as your fingernails grow
3 types of tectonic plate movement : 1. Divergent 2. Convergent 3. Transform
Divergent Boundaries Boundary between two plates that are moving apart or rifting RIFTING causes SEAFLOOR SPREADING
What is seafloor spreading? When oceanic plates diverge, (move apart) leaving room for molten material to erupt and cool This leads to the constant creation of new ocean floor This always occurs at the mid-ocean ridge
Features of Divergent Boundaries Mid-ocean ridges Rift Valleys
Rift Valley: when divergent boundaries occur on land
Great Rift Valley in Africa Volcanic mountains found along the rift include Mount Kilimanjaro, Mount Kenya and Mount Elgon extending from Jordan in southwestern Asia through eastern Africa to Mozambique 4,000 miles long, 30 miles wide