announcements no lab this week! please refer to schedule on website...
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 137Cs 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!)
Is there any scientific basis for
?
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
Whale behaviour:
?
My core score: 5/10
Earthquake? What’s up with those falling boulders?
T phase: Tertiary wave, a late-arriving short-period wave often recorded at stations of island or coastal regions. Can be caused by earthquake or submarine volcanic eruption.
http://www.whoi.edu/oceanus/
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 minutesTime through mantle: 24 hoursTime through core: 15 hours
Average speed: 94 km/h
Time to Moho (10 km): 6.4 minutesTime through mantle: 30.5 hoursTime 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.
Bathyscaphe Trieste
23 January, 1960Challenger Deep (Marianas Trench)
Pressure: 0.001 Mbar
Geode in mid mantle
?
My core score: 1/10
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: 9000oF ~ 5000oC
Are stated temperatures and pressures correct?Pressure at Moho: 8x105 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
Earth’s Magnetic Field
?
My core score: 7/10
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: 6.2x1021 Am2
If n = 100000, area = 100 m2, then I = 6.2x1020A
Assuming this is a 220V appliance, this would take 2.8TW of power (U.S. power consumption = 3.23 TW)
This might just work!!!
Project DESTINI
?
My core score: 1/10
Would a 200 MT nuclear explosion in the outer core have any effect?
At 4x106K, using ideal gas law (PV = nRT) with 1 mole H with a reaction volume of 0.01m3, 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?
The Earth will fry without a magnetic field
?
My core score: 1/10