Solid Earth 101 - A Geophysical Perspective

1. Solid Earth 101- A Geophysical Perspective Shuoshuo Han 2011-04-01

2. Formation of the Earth

3. Formation of the Earth

4. Earth’s Neighbors

5. Formation of the Earth • Take-home messages: • The big bang: 13.7 billion years ago; • Red-shift indicates the universe is expanding; • The solar system formed 4.56 billion years ago; • Planets developed from the rings of gas and dust, the planetary nebulae, that surrounded protostars. • Inner part of the solar system: rocky and metallic terrestrial planets; Outer rings: gas-giant planets; • The moon formed from debris ejected when a Mars-sized planet collided with the Earth;

6. Figure of the Earth • Shape: Oblate spheroid (the earth bulges at the equator, and is shorter at the poles) • Equatorial radius: 6378.16 km ;Polar radius: 6356.77 km; Flattening of the earth: (Re-Rp)/Re=1/298.24

7. Earth’s Structure

8. Earth’s Structure • The Earth’s interior can be divided into three layers: • Crust: thin skin that varies in thickness from 7-10 km (beneath the oceans) to 25-70 km (beneath the continents). Oceanic crust is mafic, whereas average continental crust is felsic to intermediate; • Mantle: is composed of ultramafic rocks; Major discontinuities: 410 km, 660 km • Core: made of iron alloy and consists of two parts: the liquid outer core and the solid inner core. The flow in the outer core generates the magnetic field.

9. Magnetics

10. Magnetics The Earth has a magnetic field that shields it from solar wind. Field is 30,000 nT at equator, 60,000 nT at poles Inclined geocentric dipole model accounts for ~90% of the Earth’s surface magnetic field North pole is magnetic south (field lines come out the geographic south pole and into the north) Field believed to be produced by the turbulent liquid outer core Field flips 1-5 times per million years We are believed to be in the middle of a reversal because the geomagnetic field is weakening Applications: Marine Magnetic Anomalies – leads to the idea of seafloor spreading Polar-Wander Paths – reconstruct continental drift

11. Gravity F=GMm/r2 : Universal Law of gravitation -- Falls off with 1/r 2 Range of earth’s field 978-983 Gals (greatest at the poles) Geoid: equipotential to sea level. Two methods of measuring Absolute: pendulum, simple free fall Relative measurements: springs Correct for latitude, elevation, and mass

12. Plate Tectonics • The lithosphere, the rigid outer layer of the Earth and consist of the crust and uppermost mantle, is broken into discrete plates that move relative to each other; • Lithosphere plates effectively float on the underlying soft asthenosphere • Continental drift and sea-floor spreading are manifestations of plate movement.

13. Global Earthquake Distribution

14. Major Plates of the Earth

15. Different Types of Plate Boundaries Divergent Boundaries Convergent Boundaries Transform Faults

16. Mid-Ocean Ridges

17. SubductionZone Stern 2002

18. Transform Faults and Fracture Zones

19. Different Types of Plate Boundaries

20. World’s Major Hotspots

21. Plate Tectonics • Take-home messages: • Most plate interactions occur along plate boundaries; • Three types of plate boundaries: divergent, convergent, transform faults; • Divergent boundaries are marked by mid-ocean ridges where new oceanic lithosphere forms; • Convergent boundaries: subduction zones are marked by deep-ocean trenches and volcanic arcs; Continental collision is also convergent boundary. • Transform faults: no new plate forms and no old plate is consumed. • Hotspots are places where a plume of hot mantel rock rises from just above the core-mantle boundary and cause anomalous volcanism.

22. Mantle Convection