2 The Earth’s Structureseries of layers or spheres which differ in density, chemistry (or composition) and physical properties.
3 Density is the relative heaviness of a substance Or how heavy something is for its sizedefined as the mass per unit volumeusually expressed in g/cm3EARTH HAS DENSITY STRATIFICATION
4 Evidence of the Earth’s Interior Composition Can only drill about 7.5 miles (earth’s radius = 4000 mi)Vents, volcanoes, variation in pull of gravity, etc.study of the shocks from distant earthquakes
5 Seismic Waves reveal that Earth’s Interior Is Layered If Earth were uniform (homogeneous) throughoutSeismic Waves reveal that Earth’s Interior Is LayeredIf the density, or rigidity, of Earth increased evenly with depthFigure 3.7Possible paths of seismic waves through Earth. (a) If Earth were uniform (homogeneous) throughout, seismic waves would radiate from the site of an earthquake in straight lines. (b) If the density, or rigidity, of Earth increased evenly with depth, seismic wave velocity would increase evenly with depth, and the waves would bend smoothly upward toward the surface. (c) If Earth were layered inside, some seismic waves would be reflected at the boundaries between layers while others were bent. Seismic evidence shows that Earth is layered.If Earth were layered inside
6 Compositional Layers of the Earth the Crustthin outermost layerthe Mantlethick middle layerthe Coredensest inner layercomposed mainly or iron (90%)
9 Continents and Ocean Basins Differ 2-3Continents and Ocean Basins DifferContinental crustis mainly composed of granite, a light colored, lower density (2.7 gm/cm3) rockthickerOceanic crustis composed of basalt, a dark colored, higher density (2.9 gm/cm3) volcanic rockthinner
13 Physical Properties of the Layers Not determined only by chemical compositionThe behavior of the rock (brittle or plastic) is determined mainly by temperature and pressure
14 Effects of Pressure and Temperature on Physical State of Layers 2-1Effects of Pressure and Temperature on Physical State of LayersIncreasing pressure raises the melting point of a material.Increasing temperature provides additional energy causing material to melt.Both pressure and temperature increase toward the center of the Earth, but at different rates.
15 Divisions of the Earth Based Upon Physical State 2-1Divisions of the Earth Based Upon Physical Statethe Lithospherecool, rigid outer layercomprised of continental crust, oceanic crust and the uppermost cool, rigid portion of the mantlethe Asthenospherehot, slowly flowing layer of the upper mantlethe Mesosphere (Lower Mantle)rigid layer, similar chemically to the asthenosphere but very different physicallythe Outer corethick liquid layerthe Inner coresolid layer (due to tremendous pressure)
17 What Are the Sources of Internal Heat That Keep the Asthenosphere Plastic? Radioactive decay (atoms of elements give off heat when their nuclei break apart)Internal heat moves to the surface by conduction – slow migration of heat through a material by collision of atomsAnd by convection – movement of heat in a fluid as it expands, becomes less dense and rises.
18 Figure 3.11Convection. (a) As a pot of water heats to boiling, the heated water rises. The water falls again as it cools near the surface. (b) A tectonic plate is the cooled surface layer of a convection current in the upper mantle. Plate movement is caused by the plate sliding off the raised ridges along a spreading center and by its cool, dense leading edge being pulled downward by gravity into the mantle.Fig. 3-11, p. 57