Understanding Earth's Composition and Structure

1. Geology and Nonrenewable ResourcesChapters 14Living in the Environment, 16th Edition, Miller Advanced Placement Environmental Science Edited by Ms. Wilkins, Original slide show from La Canada High School Dr. E

2. A View of Earth • Earth’s four spheres • Solid Earth • Hydrosphere • Atmosphere • Biosphere

3. Distribution of Elements • More than 100 elements in entire Earth, but 99% of Earth's mass is made up of only 8 elements Whole Earth: • Fe>O>Si>Mg>Ni>S>Ca>Al (others constitute < 1%) Earth's crust • O>Si>Al>Fe>Mg>Ca>K>Na (other constitute <1%)

4. Composition of Earth’s Crust Earth’s Crust Oxygen 46.6% All others 1.5% Magnesium 2.1% Silicon 27.7% Potassium 2.6% Sodium 2.8% Calcium 3.6% Iron 5.0% Aluminum 8.1% Fig. 10.4, p. 213

5. Earth StructureHas huge economic and Political consequences Compositional layers • Core - Fe,Ni. • Mantle - compositionally homogenous, made up of peridotite rock • Crust - compositionally heterogeneous, lots of rock types Important to understand the distribution of elements and minerals determined during earths formation. Minerals unevenly distributed because of density Also, isolated sites- ex diamonds must be exposed to extreme heat and pressure.

7. Rock Cycle Recycles scarce minerals and elements http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html

8. Igneous • Rock formed by cooling and crystallization of magma • If the cooling occurs at the surface, it is called extrusive igneous • If the cooling occurs in the Earth, it is called intrusive igneous • Extrusive igneous usually cools fairly rapidly and therefore has smaller crystals than intrusive • Examples: Granite, Basalt, Quartz, Mica, Feldspar, Obsidian http://hvo.wr.usgs.gov/hazards/dds24167_L.jpg

10. Sedimentary Rock • Rock formed by the piling of material over time • Sediment is compressed, heated and chemically changed over long period of time • Examples: Sandstone, Shale, Gypsum, Limestone, Chalk http://realgar.mcli.dist.maricopa.edu/alan/pix/grand-canyon.jpg

11. Metamorphic Rock • Igneous or sedimentary rock subjected to tremendous pressure and heat • Examples: Slate, Marble, Quartzite

12. Lithosphere • Lithosphere is divided into plates (about 13 major plates and several smaller ones). • Consists of rigid, brittle crust and uppermost mantle.

14. Plate tectonics explains wide range of geological phenomenon (volcanism, earthquakes, orogenesis, fossil distributions, etc.)Evidence for Continental Drift • Coastline fit • Alignment of mountain ranges • Similar Rock Sequences • Fossils • Modern Fauna • Ancient climates

15. Evidence for Continental Drift • Idea was revived in 1950’s and developed into Plate Tectonics • Theory of plate tectonics accepted by nearly all geologists. • Plate tectonics explains wide range of geological phenomenon (volcanism, earthquakes, orogenesis, fossil distributions, etc.)

22. Plate Tectonics • Bathymetric observations during WWII and earthquake data set stage for Plate Tectonics. • These observations are now combined to form the theory of plate tectonics.

23. Plate Boundaries • Defined by earthquake data. • Depths of earthquakes indicate types of boundaries.

24. Plate Boundaries

25. Plate Boundaries • Divergent Boundaries • Places where plates are coming apart • Convergent Boundaries • Places where plates crash or crunch together • Transform Boundaries • Places where plates slide past each other

28. Convergent Boundaries • Crust destroyed at convergent margins, mountain building • Three types: • Ocean-Ocean • Ocean-Continent • Continent-Continent

29. Ocean-Ocean Convergent Boundaries • Deep oceanic trenches

30. Ocean-Ocean Convergent Boundaries • Earthquakes define zone dipping into mantle (Benioff zone) • Zones around Pacific dipped about 45o toward the continents

32. Ocean-Continent Boundaries • Heat added to crust by magmas causes regional and contact metamorphism • Heat added also produced more felsic magma types by crustal assimilation/fractional crystallization • Stratovolcanoes built on continental crust => continental volcanic arc • Deep-sea trench and accretionary wedge (melange) along coast of continent • Examples: Andes, Cascades, Central America

33. Ocean-Continent Boundaries • Magmas produced in mantle wedge above subducting slab • Much ascending magma stalls in continental crust -> batholith (roots of volcanic arc)

34. Transform Boundaries • Most fracture zones connect segments of mid-ocean ridges • Areas of different water depth on each side of fracture zone • Shallow earthquakes occur on transforms between sections of mid-ocean ridge

35. Transform Boundaries • Connect other plate margins (convergent and divergent) • San Andreas Fault - on land transform (Pacific plate sliding north relative to North America)

38. Hot Spots • Columns of hot material rising through mantle (plumes). • Hot spot fixed in position underneath moving lithospheric plates

42. Driving Forces of Plate Tectonics • Plate movement due to Earth's attempt to lose internal heat • Conduction • *Convection

43. Driving Forces of Plate Tectonics Plate movement due to Earth's attempt to lose internal heat Conduction & Convection • Gravity-driven sliding • Plate slide down sides of mid-ocean ridge • Gravity gives the push, not magmas at ridge • Ridge push is probably the main force on plates

44. Flow of material associated with hot spot plumes drives plates • Columns of rising material vs. convection cells • Chaotic convection in mantle (plumes of rising material)

46. EARTHQUAKES http://www.howstuffworks.com/earthquake6.htm

47. Earthquakes Most destructive forces on Earth. But it is buildings and other human structures that cause injury and death, not the earthquake itself 1988 - Soviet Armenia: magnitude 6.9, 25,000 people died 1985 - Mexico City: magnitude 8.1, 9500 people 1989 - Loma Prieta, CA: magnitude 7.1, 40 people died 1995 - Kobe, Japan: magnitude 7, ~6000 people died

48. 30,000 earthquakes occur worldwide annually that are strong enough to be felt Typically only 75 of them are considered to be significant

49. Vibration of earth produced by rapid release of energy (seismic waves) with radiate in all directions from the source (focus) • Like ripples from dropping a stone in a pond, energy dissipates with distance • Earthquakes don't occur randomly. Occur on faults or fractures within the earth • Explained by plate tectonics. Most occur on plate boundaries • Sometimes in plate interiors if enough stress is built up

50. Types of Waves Earthquake waves = seismic waves. Recorded on seismometers on seismographs. Types of Waves • Surface waves - travel on Earth's surface, away from epicenter. • Very slow waves. Cause a lot of damage, rolling feeling at end of earthquake • Body Waves - travel through Earth's interior, spread outward from focus