How Do We Know What It Is Like Inside The Earth?

1. How Do We Know What It Is Like Inside The Earth? Pre-GPT scientific thought on the Earth before 1950 Department of Geological Sciences San Diego State University

2. What direct evidence tells you aboutthe inside of the Earth?

3. How Symmetrical Is the Earth?

4. How Symmetrical Is the Earth?Very, a the rotation about its axis is fairly smooth Symmetry would be imposed by initial spinning while molten Any reasonable Earth model proposed must be symmetrical

5. The Interior Temperature of the Earth • Is the inside of the Earth hot or cold? • What evidence is there for this?

6. Evidence that the Earth is hot inside: Hot Geysers Volcanoes Hot sulfurous gasses from vents

7. Deep Mines Evidence that the Earth is hot inside: The temperature in all deeper mines increases with depth: About 30 oC per 1000 m This image is in a South African Gold mine 3km or 2 miles deep in the Earth. The temperature is 49 C or 120 F The limit to the depth of a deep mine is when the temperature is to hot for stand Deepest mine is 3,585 m or 11,762 ft

8. Deepest mines only extend a tiny fraction into the average thickness the crust, never mind the rest of the Earth Deepest Mine 3.4 km . Earth Radius~ 6,400 km

9. What About Magnetism? • Is the Earth’s magnetic? • What sort of properties does it have? • Could you detect the Earth’s magnetic field

10. The Earth’s Magnetic Field: by compass Age of Exploration, 1400-1600, also discovered the compass and Earth’s magnetic field.

11. Magnetic Dip:the angle that magnetic linesleave or enter the Earth

12. Aurora Borealis and Aurora Australis,northern and southern lights

13. Most frequent is near 67 N and S latitude Maximum N. Pole Coverage Earth’s magnetic field must be deep inside, And uniform and symmetrical to cause symmetrical compass variations and the Auras Borealis and Australis Maximum S. Pole Coverage

14. What can gravity tell usabout the Earth? I am So proud Sir Isaac Newton Published his Philosophiae Naturalis Principia 1686 which included the definitive statement on gravitation

15. Basic Gravity: Any two bodies in the universe attracted each other with a force that is GREATER if either is more MASSIVE GREATER if they are CLOSER Hey, this Took a lot of work Force, equal and opposite Force, equal and opposite

16. Gravity: The Formula G Memorize this for the quiz m2 D m1

17. Cavendish’s 1789 Experiment to Determine the Mass and Density of the Earth Earth mass Ball mass * Use torsion balance to measure the force between 4 iron balls * Measure the size and mass of the iron balls * Calculate “constant” in gravity formula G Ball weight Earth Earth Radius Earth Mass = 6 x 10 24kg Earth Average Density = 5.54 g/cm3

18. Cavendish’s 1789 Experiment to Determine the Mass and Density of the Earth:What does this mean? Earth Average Density = 5.54 g/cm3 Earth You should see this on my Facebook Henry Cavendish ~ 1789

19. Cavendish’s 1789 Experiment to Determine the Mass and Density of the Earth:What does this mean? Water = 1 g/cm3 Earth Surface rocks as Basalt, Granite ~ 3 g/cm3 Earth Average Density = 5.54 g/cm3 Deeper Rocks must be much denser than 5.54 g/cm3 to compensate for lighter surface rocks

20. What is the material at the center of the Earth? Iron -Nickel The Earth is thought to be similar to Meteorites, about 5% of the meteorites are Iron-Nickel metal. These are believed to have been the center of former bodies in space where the Iron-Nickel, a dense material, settled to the center when the body was molten. A later collision broke apart the body into many small parts. Iron-Nickel meteorite found in Oregon

21. Gravity is significantly affectedby masses close to the Earth’s surface – even only a kilometer or so under ground Earth’s Radius 6,500 km

22. Ore bodies near the surfacewill cause gravity to be more and less –a way of searching for them

23. The BritishGreat Arc Meridian Survey of India 1803-50

24. The British discovered that their plumb bobs were not pointing toward the center of the Earth What could be an explanation?

25. Plum bobs, gravity and floating George Airy John Pratt Airy and Pratt proposed different explanations for the nature of the crust. Airy hypothesized that there was a uniform density crust to the Earth and it varied in thickness – he was more right.

26. Isostasy and Floating Analogy: The crust floats on the mantel. A plate floats on a portion of mantle. Figure 2-5

27. Crust, Mantle, Core, Plates all - floatwith lighter on top, heavier below:Just as objects do in water Principle of Isostacy: “A body that is less dense than a surrounding fluid will displace a volume of the fluid equal to that body’s mass”

28. What Can Sound Tell Us? Hint: Earthquakes are mostly sound energy Earthquakes are used to probe the interior of the Earth, somewhat as a bat uses sound not only to detect the presence of objects but about the objects’ size and nature.

29. • Primary (P) waves: - compressional - analogy is sound waves • Secondary (S) waves: - transverse (analogy is ocean waves) - ~1/2 velocity of P waves - do not pass through liquid • By the way, surface waves (a third type slower than above two) cause the big disasters (Garrison, 1993)

30. Prediction for Homogeneous Earth Structure Observation from Global Seismological Networks (Garrison-3.7Top) (Garrison, 1993)

31. (Pink Floyd, 1973)

32. (Pink Floyd, 1973) .

33. Connect the dots: Then you get curves oftemperature, density, P and S speed, properties and molecules Crust

34. The End