Formation of Earth

1. Birth of the Solar System Nebular Theory Nebula compresses Rotation flattens nebula Collapse into center formed solar nebula and finally, the sun Condensation formed planets, planetesimal, moons and asteroids during planetary accretion around 4.6 billion years ago (Meteorites are iron-rich or rocky fragments left over from planetary accretion) Formation of Earth See Fig. 1.9 (a), (b) and (c) http://www.psi.edu/projects/planets/planets.html

2. Orion Nebula www.hubblesite.org www.geol.umd.edu/~kaufman/ ppt/chapter4/sld002.htm www.psi.edu/projects/ planets/planets.html See Fig. 1.9

3. Formation of the Planets • Nuclear fusion began within the mass at the center of the solar system forming the sun • The inner planets were hotter and gas was driven away leaving the terrestrial (rocky) planets • The outer planets were cooler and more massive so they collected and retained the gasses hence the “Gas Giants” Terrestrial Planets ? Gas Giants www.amnh.org/rose/backgrounds.html

4. Differentiation of the Planets • The relatively uniform iron-rich proto planets began to separate into zones of different composition: 4.5bya • Heat from meteor impact, pressure and radioactive elements cause iron (and nickel) to melt and sink to the center of the terrestrial planets See Fig 1.10

5. Further Differentiation of Earth Deepest Mine Deepest Well Continental Crust (Silicic) • Lighter elements such as Oxygen, Silicon, and Aluminum rose to form a thin, rigid crust • The crust, which was originally thin and basaltic (iron rich silicate), further differentiated to form continental crust which is thicker, iron poor, silica rich and lighter Oceanic Crust (Basalt) Mid-Ocean Ridge (New Crust) See Fig. 1.11

6. Element (Atomic #) Chemical Symbol % of whole Earth % of Crust (by Weight) Change in Crust Due to Differentiation Oxygen (8) O 30 46.6 Increase Silicon (14) Si 15 27.7 Increase  Aluminum (13) Al <1 8.1 Increase  Iron (26) Fe 35 5.0 Decrease Calcium (20) Ca <1 3.6 Increase  Sodium (11) Na <1 2.8 Increase  Potassium (19) K <1 2.6 Increase  Magnesium (12) Mg 10 2.1 Decrease All Others ~8 1.5 Composition of Earth and Crust Before and After Differentiation

7. Crust and MantleLithosphere and Asthenosphere • The uppermost mantle and crust are rigid solid rock (Lithosphere) • The rest of the mantle is soft but solid (Asthenosphere) • The Continental Crust “floats” on the uppermost mantle • The denser, thinner Oceanic Crust comprises the ocean basins Figure 1.11, Detail of crust and Mantle

8. A Large Variety of Rocks (and Sediment)Products of an Active Planet Crust: Rigid, Thin Earth’s structure leads to intense geologic activity • Inner core: Solid iron • Outer core: Liquid iron, convecting (magnetic field) • Mantle(Asthenosphere): plastic solid, iron-magnesium silicate, convecting • Crust(Lithosphere):Rigid, thin • O, Si, Al, Fe, Ca, Na, K, Mg… Mantle: Plastic, Convecting 47%, 28, 8, 5, 4, 3, 3, 2

9. Lithospheric Plates • The Lithosphere is broken into “plates” (7 maj., 6 or 7 min.) • Plates that “ride around” on the flowing Asthenosphere • Carrying the continents and causing continental drift See Kehew, Figure 1.19

10. Lithospheric Plates Fig. 1.13 and 2.14

11. Three Types of Plate Boundaries • Divergent • Convergent • Transform See Fig. 1.14 and 1.13

12. Things to Know About Plate Tectonics • Composition and properties of Zones • Iron core (solid & liquid, convecting, magnetic field) • Mantle: Plastic solid, convecting, ultramafic (Si, O, Fe,Mg) • Composition and Properties of the Crust • Oceanic Crust: Basalt, Thin (5-10km) (O, Si, Fe, Mg, Ca) • Continental Crust: Granitic, Thick (10-50km) (O, Si, Al, Na, K)

13. Things to Know About Plate Tectonics • Features and Geologic Phenomena • Convergent: trenches, mountain chains, granitic magma, granitic rocks, composite volcanoes, • Divergent: Mid ocean ridges, rift valleys, shallow earthquakes, basaltic magma and lava, basalt, lava floods (volcanoes rare)

14. Things to Know About Plate Tectonics • Features and Geologic Phenomena • Transform: Offset ocean ridges or mountain chains, shallow earthquakes, no magma or lava • Hotspots: Shallow earthquakes, basaltic magma and lava, basalt, lava floods, sometimes shield volcanoes

15. Igneous Rocks: When rocks melt, Magma is formed, rises, cools and crystallizes. Sedimentary Rocks: All rocks weather and erode to form sediments (e.g., gravel, sand, silt, and clay). When these sediments accumulate they are compressed and cemented (lithified) Metamorphic Rocks: When rocks are compressed and heated but not melted their mineralsre-equilibrate (metamorphose) to minerals stable at higher temperatures and pressures The3 rock typesform at convergent plate boundaries Sedimentary Rocks Metamorphic Rocks Igneous Rocks Magma

16. The Rock Cycle Geological Materials Transformation Processes • Geologic materials (blocks) • Are transformed and transported • By geologic processes (arrows) • To form other geologic materials • Driven by internal and external processes Fig. 3.1 See Fig. 1.15

17. Igneous and Sedimentary Rocksat Divergent Boundaries and Passive Margins • Igneous Rocks (basalt) are formed at divergent plate boundaries and Mantle Hot Spots. New basaltic, oceanic crust is generated at divergent plate boundaries. • Sedimentary Rocks are formed along active and passive continental margins from sediments shed from continents • Sedimentary Rocks are formed on continents where a basin forms and sediments accumulate to great thicknesses. E.g., adjacent to mountain ranges and within rift valleys.

18. Learning Plate Tectonic Geography • Brushing up on basic geography will help you learn Plate Tectonics • Once you know your basic geography and ocean basin features (Mid Ocean Ridges, -Oceanic Trenches) you can • Learn the 7 major plates • Learn the types of plate boundaries • Learn why those features are where they are