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Transcript
Layers of Earth and Convection Currents How have geologists learned about Earth’s interior structure and what causes convection currents in the mantle? Earth’s Interior Geologists have used two main types of evidence to learn about Earth’s interior. 1. Direct evidence from rock samples (drilled from deep inside Earth) 2. Indirect evidence from seismic waves (produced by earthquakes; speed gives clues to the material) Three main layers of Earth vary greatly in size, composition, temperature and pressure. They are the crust, mantle and core. The Layers of Earth Crust Mantle Core • Solid rock, outer “skin”, includes dry land and ocean floor • CRUST: 2 types: Oceanic (more dense basalt) or Continental (less dense granite) • Layer of solid, hot rock 40 km beneath the surface; divided into layer • LITHOSPHERE = solid upper mantle + crust about 100 km thick • ASTHENOSPHERE = hot, soft, “taffy-like” part; the plates move on it when driven by convection currents; under increased pressure • Lower Mantle = solid, extends to the core • Outer Core (liquid/molten Fe and Ni) • Inner Core (dense ball of solid Fe and Ni) • Movement of liquid outer core creates Earth’s magnetic field Layers of Earth Two Types of Crust Oceanic Crust Continental Crust Rock Type Basalt Granite Color Dark Light Composition Low Si, High Fe High Si, Low Fe Density High Low 6-7 km, avg. 40 km, avg. Floats lower in the mantle – form basins that fill with water Floats higher in the mantle Average Thickness Depth (general) Convection and the Mantle Heat Transfer: 3 Types are... Radiation – transfer of energy through empty space, has no direct contact between the heat source and an object (Ex: sunlight warming Earth’s surface) Conduction – heat transfer by direct contact of particles of matter (Ex: metal spoon heating up in a pot of hot soup) Convection – transfer of heat by the movement of a heated fluid (includes liquids and gases); Heat transfer is caused by differences in temperature and density within a fluid (Ex: Water on a stove – water heats at the bottom of the pan, becomes less dense and rises; away from the heat source the water cools, becomes more dense and sinks; the process begins again) This is a Convection Current, or flow that transfers heat. Density – measure of how much mass there is in a volume of a substance Convection Currents in the Mantle The heat source is the Earth’s core and from the mantle itself. These currents have been acting like a conveyor belt moving the lithosphere above for the past four billion years