Presentation on theme: "Announcements No lab this week! Please refer to schedule on website (instruct.uwo.ca/earth-sci/023-> Revised lab order) Next week’s lab: Radioactivity."— Presentation transcript:
Announcements No lab this week! Please refer to schedule on website (instruct.uwo.ca/earth-sci/023-> Revised lab order) Next week’s lab: Radioactivity experiment (detection of 137 Cs samples in a sandbox) Thursday: Midterm Exam
Midterm Exam: Thursday Multiple choice, 30 questions In class – please place backpacks etc. at front of class before sitting, but keep your student card Bring HB pencil, eraser & calculator Section: mark 023 or 123, as appropriate
What should I study? There are 5 questions that require a calculator. The remaining 24 questions are general knowledge taken from the lecture material (1 from the lab material) You will be given a Periodic Table if needed Some questions will relate to movies shown in class One bonus question from the Scugog lecture (but maximum mark is 30/30!)
Your task Identify 3 correct and 3 incorrect statements about Earth ’ s interior Assume that the technology is possible
Why here? Is this the best launch location for a ship to go to the centre of Earth??
The Marianas Trench marks where the fast-moving Pacific Plate converges against the slower moving Philippine Plate. The Challenger Deep, at the southern end of the Marianas Trench, plunges deeper into the Earth's interior (nearly 11,000 m) than Mount Everest rises above sea level (about 8,854 m). http://pubs.usgs.gov/publications/text/understanding.html
Marianas Trench: crustal thickness ~10 km Seismically active region
…but Earth’s radius is smaller (by 21.3 km) at the poles...
Choice of launch location: ? My core score: 6/10
Is this normal whale behaviour? How fast and how deep can whales swim?
Blue whales: - travel in small pods - can swim up to 48 km/h - can dive to depths of 105 m - use low-frequency sounds to communicate and locate krill
Submarine debris flow: maybe Falling boulders: no way! Puerto Rico Trench
Earthquake and falling boulders ? My core score: 5/10
Is this schedule accurate? Time to Moho: 15 minutes Time through mantle: 24 hours Time through core: 15 hours Average speed: 94 km/h Time to Moho (10 km): 6.4 minutes Time through mantle: 30.5 hours Time through outer core: 24 hours
Is this schedule accurate? Not too bad, for Hollywood!
Schedule/basic Earth structure: ? My core score: 7/10
Giant crystal cavern in the mid-mantle. Yeah right!
Geode: a hollow rock (usually spherical) with crystals lining the inside wall.
Giant crystal cavern in the mid-mantle. Yeah right! Pressure too high (~ 0.5 Mbar) Such large cavities would be seismically detectable.
Diamond the size of Cape Cod Virgil being damaged Do diamonds exist in the lower mantle?
http://www.syd.dem.csiro.au/research/mantle/DI_explore.html Diamonds are a high- pressure form of graphite (carbon) Diamonds form at depths > 100 km They are usually brought to the surface by rare volcanic eruptions (kimberlites) Diamonds from the deep mantle have recently been recognized!
Diamond the size of Cape Cod … but are they the size of Cape Cod?
Giant diamonds in lower mantle ? My core score: 7/10
Are stated temperatures and pressures correct? Temperature in outer core: 9000 o F ~ 5000 o C
Are stated temperatures and pressures correct? Pressure at Moho: 8x10 5 PSI ~ 55 kbar Actual lithostatic pressure at Moho: 4-12 kbar Note: The core is more dense than the mantle!!!
Temperatures and pressures ? My core score: 5/10
Is Earth’s magnetic field generated in the core?
Yes! But the so-called geodynamo is much more complex than depicted in the Core. http://science.nasa.gov/headlines/y2003/29dec_magneticfield.htm
Could the geodynamo be stopped by a giant electromagnet hidden somewhere in Alaska? Beams high-powered electromagnetic energy waves down fault lines to trigger earthquakes Project DESTINI
Could the geodynamo be stopped by a giant electromagnet hidden somewhere in Alaska? Project DESTINI “We need to suck up every drop of juice east of the Rockies to fire up DESTINI”
Project DESTINI Earth’s magnetic dipole moment: 6.2x10 21 Am 2 If n = 100000, area = 100 m 2, then I = 6.2x10 20 A Assuming this is a 220V appliance, this would take 2.8TW of power (U.S. power consumption = 3.23 TW) This might just work!!!
Would a 200 MT nuclear explosion in the outer core have any effect? At 4x10 6 K, using ideal gas law (PV = nRT) with 1 mole H with a reaction volume of 0.01m 3, I calculate an explosive pressure of 32.5 kBar Since this is less than the pressure in the outer core, the nuclear bomb would actually do pretty much nothing.
Restarting the geodynamo using nuclear weapons ? My core score: 0/10
Would sudden loss of Earth’s magnetic field allow cosmic death rays to zap the Golden Gate Bridge?