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

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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:

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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:

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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

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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:

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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

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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

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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

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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

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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

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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

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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

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My core score: 1/10