SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond

1. SPU-22: The Unity of Science from the Big Bang to the Brontosaurus and Beyond Lecture 14 26 March 2014 Science Center Lecture Hall A

2. Outline: Victory Of Continental Drift (nka “Plate Tectonics”) Magnetism’s key contributions: History Plate tectonics: Evidence developed for (near) complete acceptance by late 1960s Some applications of new paradigm: Island-arc origins (Hawaiian example); transform faults; plate collisions Plate motions today: VLBI and SLR battle to measure first

3. Where Are We? Wegener “pushed” idea of continental drift until untimely death. He had “fuzzy” ideas on how continents ploughed through ocean basins; these – and other details – mocked by many scientists of day; including Jeffreys. Holmes proposed convection cells within mantle. Sort of ignored.

4. What Happened Next? World preoccupied with WW II. But techniques developed. Techniques for studying ocean and for detecting magnetic effects (can you guess why?) Developments in magnetism would play bigger role postwar: • Phenomenon of thermoremanent magnetism • Properties of earth’s magnetic field

5. Properties Of Earth’s Magnetism: I Thermoremanent magnetism of rocks: When first cooled (solidified) retains imprint of magnetic field strength and direction of earth’s field at that time and location, mainly due to iron in rock

6. Properties Of Earth’s Magnetism: II Earth’s magnetic field reversed polarity (N to S and v.v.), after of order 100,000+ years; spacing apparently very irregular in time; changeover took of order 10,000 years. Discovered in 1906 by Brunhes; first studied systematically by Matuyama in 1920s See demonstrations of magnetism: Analogy of earth with bar magnet; rock’s magnetism. See next slide for schematic of earth’s magnetic field

7. Schematic Of Earth’s Magnetic Field

8. In WWII (And Following) New, More Sensitive And Compact, Magnetic Detection Techniques Developed And Yielded New Results Measurements were made on rocks from all over globe. Magnetic-pole positions determined from rocks of different ages, obtained from same continent, differed by large amounts: polar wander or continent drift? (See next slide.) However, rocks of same age from different continents gave different pole positions which changed differently with age of rocks. (See next slide plus one and two.) Obvious interpretation: the continents moved! Moreover, as Wegener first observed, paleoclimatic and paleomagnetic results were in agreement.

9. Schematic Of Polar Wander vs. Continental Drift

10. Data On Pole Movement For Europe And North America

11. Magnetic Pole Motion Appearance From Continental Drift

12. Magnetic Results Defended Several independent groups in different countries verified that instruments were reliable, measurements were reliable, and interpretations were also reliable. Game over? Everyone converted to drifting? Not on your life! The wheels of justice grind slowly, as well as finely. But pendulum was swinging and picking up some speed towards drifters

13. The Battle Moves to the Seas After World War II, funding for ocean research also blossomed (you can guess why) Explosive increase in data, based on new instrumentation such as sonar, and research ships plowing through oceans (Difficult to step back and think; data flow was at times overwhelming)

14. Geopoetry In 1960, Harry Hess proposed scenario which he called “Geopoetry.” Disclosure from mapping of seafloor was existence of mid-ocean ridges (see next slide). He thought that molten lava emerged from these ridges and pushed aside existing seafloor with ends of seafloor exiting back into mantle at trenches, also disclosed from studies of ocean floor (see cartoon on next slide plus one)

15. Mid-Ocean Ridges And More

16. Earth Cross Section: Schematic

17. Harry Hess (1900-1970)

18. How Did Hess’s Proposal Play in Peoria? Not very well in many quarters. Typical skeptic noted that two “wrongs” (continental drift and stable, global, mantle convection) do not equate to one “right” Old guard does not go gently into night like old generals

19. Sea-Floor Spreading: Proposed Test Morley (1963; publication rejected) and Vine &Mathews (1963) noted consequence of sea-floor spreading: Remanent magnetism of ocean-floor rocks should show same “striped” pattern on both sides of mid- ocean ridges, with oldest rocks being furthest from ridges. (See next slide.)

20. Cartoon Of Sea-Floor Spreading

21. The Final Nail: Eltanin 19 Research ship (next slide) with magnetometers lowered near seafloor traced out pattern of magnetic fields. (See next slide plus one.) Testing Vine-Mathews (&Morley) prediction not even mentioned in research proposals for ship. Experimenters didn’t realize, at first, what they had What about ages? Supported theory via timing of magnetic-field reversals compared with surface results. Enabled average spreading rate determinations: ~4.5 cm/yr, over >100,000 year intervals: from known time interval and width of rock pattern

22. Ship Eltanin Carried Out Test “Accidentally”

23. Magnetic Anomalies Measured By Eltanin 19

24. The Sequel All over but shouting in late1966 Continental drift, now known as plate tectonics, was declared winner by knockout: Major geologist/geophysicist opponents dropped off lists of anti-drifters like rocks sinking in water New, incredibly rich paradigm has invigorated earth sciences for past four + decades and has not disclosed any signs of slowing up

25. What Are Some Consequences Of This Revolution? Hot spots and origin of island arcs (e.g., Hawaiian; see next three slides) Transform fault concept (following two slides) Effects of collisions better examined (next following two slides)

26. Earth’s Plates And Hot Spots(Connection With Island Formation)

27. Hawaiian Islands

28. Age of Hawaiian Islands

29. Transform Fault: San Andreas

30. Transform Fault: San Andreas(Picture Of Part)

31. Collision Between India And Asia

32. Himalayas

33. What Are Plates Doing Now? What and where are the plates (next slide)? Dating led to broad sweep of time history, with crude time resolution How do we get contemporary fine resolution? - Technology developments pave the way: radio antennas, low noise receivers, atomic clocks, and computers: all vital for Very Long Baseline Interferometry. Idea conceived in 1966 (see next slides for some basic details) - Competing technique: satellite laser ranging (see later slides; idea followed that for VLBI)

34. Plate Boundary Motions (>360°)

35. Basic Principles 0f VLBI

36. VLBI Data Acquisition

37. Two “Strings” Of VLBI Data (One From Each Of Two Antennas) Random (not aligned) Random (aligned) ++-+--- +--+--- -++--++ +--+--- Sum of the products Sum of the products of the two strings tends of the two strings to zero “builds up” (save for noise) Note: + times + = 1; - times - = 1; - times + = + times - = 0

38. Modern VLBI Antenna

39. SLR Tracking System

40. SLR Tracking Station

41. Transportable Satellite Laser Tracking Site(Southern California)

42. Satellite Laser Ranging (SLR) Targets

43. Lageos Satellite With Corner Cubes

44. SLR vs. VLBI Which technique would be first to yield reliable results (note false claims) for plate motions?? The winner by several years is … VLBI (1985; see next slide)

45. Baseline: Haystack Observatory, MA To Onsala Observatory, Sweden