1. GE 11a, 2014, Lecture 5 Spherical structure of the earth

3. The earth, ca. 1800

4. Nevil Maskelyne and the Schiehallion experiment (1774) Schiehallion (‘Sidh Chailleann’) Scotland Nevil Maskelyne doing his impression of Ben Franklin MsMs  F = m. g. tan(  ) = G. m. M s /d 2 F m.gm.g d m. g = G. m. M E /R E 2 M E = (R E 2 /d 2 ). (M s /tan(  )) ~ 6. 10 24 kg R E = 6.37. 10 6 m; V E = 1.1. 10 21 m 3  ~ 5.5 g/cm 2 (initially found ~ 4.5)

5. Densities of common substances (all in g/cc) Ice0.917 Water1.000 Seawater1.025 Graphite2.200 Granite~2.70 Titanium4.507 Iron7.870 Copper8.960 Mercury13.58 Gas: proportional to P/RT Two options: sub-equal mix of metal and rock or… an ideal gas, w/ high density at high P (B. Franklin)

6. Period of precession Period of spin Torque (sun and moon trying to pull earth’s tidal bulge into plane of ecliptic) Moment of inertia I =  i m i. r i 2 mimi riri Higher Lower Earth has I much less than expected for homogeneous sphere Mass distribution in earth’s interior

7. Kraemer, 1902 View combining known density, moment of inertia, oblateness, rigidity of surface rocks, and topography Note bad for a bunch of turn-of-the-century quacks!

8. Focus Mantle Seismograph Core SP “sample” outer ca. 200 km, but most energy in upper 10 km

9. A mechanical seismograph

10. Minutes Surface waves 0 PS 1020304050 ‘Primary’ (first to arrive) ‘Secondary’ (second to arrive) Anatomy of a seismic signal

11. Amplitude =23 mm Richter magnitude Amplitude (mm) Interval between S and P waves (s) Distance (km) P S S-wave interval = 24 secondsP-wave measure the amplitude of the largest seismic wave… …and the time interval between the P- and S-waves (I.e., the distance from the epicenter. Connect the points to determine the Richter magnitude.

12. Real data is more complicated…

14. Look at your notes, John!

20. Mg 2 SiO 4 in upper mantle Mg 2 SiO 4 in lower mantle

21. The core’s density is less than that of pure Fe. Requires a low-mass Alloying agent. S? O? H? ???

22. The events in early earth history that controlled core/mantle segregation

24. Robin Canup’s movie Animation of Theia forming in Earth's L5 point and then drifting into impact. The animation progresses in one-year steps making Earth appear not to move. The view is of the south pole.

27. Evidence for the ‘magma ocean’ stage of the earth is essentially erased by later convection, plate formation, subduction, etc. But the moon’s crust preserves evidence planets are largely liquid early in their history.

28. And today Io, a moon of Jupiter, seems to possess a partially crystallized magma ocean, supported by tidal heating