Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Spherical Earth wikipedia , lookup
Post-glacial rebound wikipedia , lookup
History of geomagnetism wikipedia , lookup
History of geology wikipedia , lookup
Age of the Earth wikipedia , lookup
Ionospheric dynamo region wikipedia , lookup
Magnetotellurics wikipedia , lookup
Mantle plume wikipedia , lookup
66 Experiential Science 10—Terrestrial Systems The Franklin and Mackenzie mountains in the NWT are part of the continuous chain of mountains extending through the western part of North and South America. These mountains formed when island chains and small continents collided with the ancient North American plate about 185 million years ago and again about 100 million years ago. Plate Motion and Convection Currents The Earth’s lithosphere (the crust and the outer layer of the mantle) is thin, cool, and strong compared to the molten layer of the asthenosphere below it. Inside the asthenosphere, magma is slowly heated by the Earth’s hot core or by radioactive decay. As it is heated, the asthenosphere rises up away from the Earth’s core. When it nears the lithosphere it flows sideways, becomes heavier, and sinks again. This change in movement creates swirling currents of heat in the asthenosphere called convection currents. Scientists know that convection currents in the Earth are at least partially responsible for the movement of plates, but there is still much to find out about how the plates move and how convection currents work. For example, it is known that sometimes heat from the molten asthenosphere does not move evenly in convection currents but comes to the surface as gushes of hot material that melts through the middle of plates, rather than escaping out from the edges. These are called mantle plumes. The plume melts the plate like a blowtorch, and a volcano forms above it. As the The Hawaiian Islands are an example of a chain of volcanic islands produced by plumes of molten material erupting from the asthenosphere. SCIENTIFIC TERMS convection current: a current caused by the difference in temperature from the bottom to the top of the Earth’s mantle, which in turn causes plate movements. Chapter 1 Geologic Time and Earth Dynamics67 plate slowly moves, the plume melts through another part of the plate, producing a chain of volcanic islands. This is called a hot spot. Hawaii is an example of a chain of islands caused by hot spot activity. The Earth’s plates move at different rates, but in continuous directions, not randomly. Asthenosphere Lithosphere (crust and upper mantle) Figure 1.22 Convection currents in the asthenosphere. The red arrows show the movement of the convection currents while the white arrows show the Earth’s plates moving due to the convection currents below. Activity 13 field activity 4 lab activity library activity classroom activity chapter activity 4 research team activity Convection Currents SAFETY PRECAUTION Be sure to wear safety goggles when handling the oil, since you will be heating it. Purpose To investigate convection currents and how they play a role in plate motion. Materials and Equipment • 300 ml oil • 1 tablespoon dried spices such as basil or oregano • 1-litre heat-proof clear beaker • ring stand with ring holder •candle/matches • safety goggles Procedure 1. In your research teams, pour the oil into the beaker and sprinkle the spices on top of the oil. Place the candle on the base of the ring stand and the beaker on the ring holder. Position the ring so that it is just above the flame level of the candle. 2. Light the candle and wait for several minutes while the oil heats up. Remember to wear your safety goggles! As the oil heats, describe the movement of spices in the oil. The oil represents the molten mantle and the spices are used to show the movement of convection currents in this molten material. 3. Record your findings and explain how this experiment simulates convection currents in the asthenosphere. Conclusions 1. What are 3 everyday examples of convection? 2. Describe the ways in which the lithosphere interacts with convection currrents in the asthenosphere.