Planet Earth in Profile The Layered Interior

Objectives Explore evidence that helps explain Earth’s internal structure. Outline Earth’s internal layers and discuss some of the evidence leading to their discovery Introduce the salient properties of Earth’s outer layers, its crust and the underlying mantle Investigate the processes at work to modify Earth’s surface, creating physical landscapes of great diversity

Evidence of Earth’s Internal Structure Earthquakes – Shaking and trembling of Earth’s surface caused by sudden release of stress within the crust Seismic waves – Surface waves Travel along the surface – P-waves (primary waves) Back-and-forth; Compressional Travel trough liquids and solids – S-waves (secondary waves Up-and-down; right angles Travel through solids only

Evidence of Earth’s Internal Structure Seismic Waves – 0° to 103° Find P- and S-waves only – 104°-142° Shadow zone No P-waves; bend due to higher density of mantle No S-waves; cannot pass through liquid – 142°-180° Find P-waves only No S-waves; cannot pass through liquid

Earth’s Internal Layers Core – Inner core Solid; Iron (Fe) and Nickel (Ni) 1220 km (760 mi) radius; 5150 km (3200 mi) depth – Outer core Liquid; Iron (Fe) and Nickel (Ni) 2250 km (1400 mi) thick; 2900 km (1800 mi) depth Mantle – Lower mantle Solid; Iron (Fe), Magnesium (Mg), Silicon (Si) 2230 km (1385 mi) – Upper mantle Solid-plastic-solid; Iron (Fe), Magnesium (Mg), Silicon (Si) 670 km (415 mi) depth [Insert Fig ]

Earth’s Outer Layer Mohorovicic discontinuity (Moho) – The density has a marked different between the crust and mantle Earthquake waves speed up when passing from crust to mantle Indicates mantle is more dense than crust – Made it possible to measure the thickness of the crust Thickness varies From 5 km (3 mi) to 40 km (25 mi)

Earth’s Outer Layer Crust – Continental crust Felsic – Feldspar rich (granitic) Light colored Low density (2.8 g/cm3) – Oceanic crust Mafic – Magenisum (Mg) and iron (Fe) rich (basaltic) Dark colored Higher density (3.0 g/cm3) [Insert Fig. 27.7A - felsic] [Insert Fig. 27.7B - mafic ]

Earth’s Outer Layer Lithosphere – Rigid layer – Crust and uppermost mantle Asthenosphere – Plastic layer; flows readily Lithospheric Plates – Large, rigid fragments – Move over asthenosphere Insert Fig. 27.8

The Crustal Surface Topographic Relief – Vertical difference between highest and lowest elevation – High relief Large difference from high to low relief – Low relief Small difference from high to low relief Insert Fig low relief

The Crustal Surface Topographic Relief – Vertical difference between highest and lowest elevation – High relief Large difference from high to low relief – Low relief Small difference from high to low relief

The Crustal Surface Continental Shields – Large, stable, low relief expanse of land – Old metamorphic, igneous rocks North American Shield – Canadian (Laurentian) shield

The Crustal Surface Orogenic Belts – Series of linear mountains – Zones of high relief Weathering – Physical, chemical breakdown of rocks Erosion – Removal of weathered rocks