Graduate Student Welcome Week

September 9, 2015

Introduction – Olivia Jensen

about Olivia…about Olivia…

• Born… in the deep winter of 1943 in a farmhouse Born… in the deep winter of 1943 in a farmhouse in Springbank, Albertain Springbank, Alberta

• Educated… in the public schools of Calgary, Educated… in the public schools of Calgary, Vancouver and at the University of BCVancouver and at the University of BC

• Joined McGill’s Faculty of Engineering in 1973 Joined McGill’s Faculty of Engineering in 1973 and then Faculty of Science in 1984and then Faculty of Science in 1984

• Married: 1975 – son of 35, daughter of 33, both Married: 1975 – son of 35, daughter of 33, both McGill graduates; grandson 7, granddaughter 4McGill graduates; grandson 7, granddaughter 4

• Divorced: 1989 Divorced: 1989 • ““Transition”: 1989 with some following medical Transition”: 1989 with some following medical

interventionsinterventions

Questioning the FaithElements of faith in geology and geophysics

• Uniformitarianism• Layered structure• Magnetic field generation• Interior rheology• Age, formation, composition• Interior mineralogy and temperature

Answering the questionsPrinciple of Uniformitarianism

•Generalized covariance is inherent to the two great theories upon which our physics is constructed:Quantum MechanicsGravitation (General Relativity)

•These two theories are thought to be only insufficient to describe nature before 10-33 seconds following the Big Bang.

•They have, so-far, failed no empirical tests.•Geological and geophysical processes since BB+10-33s follow the “laws” of physics... hence PofU?

Answering the questionsLayered Structure

• Seismology finds global radial variations in physical properties α and β at many nearly fixed depths within the Earth.

~5-70 km410 km660 km~2700 km ±2890 km5150 km

Answering the questionsInterior Rheology

•Isostatic recovery from glacial loading and lateral tectonic plate motions suggest a different layering, especially of the outer regions.

0 – 200 km (~elastic)to ~400 km (~low viscosity fluid) to ~2900 km (~higher viscosity)to ~5100 km (very low viscosity)to 6375 km (~soft elastic)

Rheological hack: eshear

= (t/2η + 1/2μ)σshear

Seismic provisosSeismic technologies are not as powerful as we

might like to believe

What Lies Deep in the Mantle Below?

“Teleseismic tomography, although sensitive to horizontal variations in seismic wave speed, has virtually no ability to determine depth variations.”

...but still

“Were it not for seismology, we would be almost totally ignorant of the structure of the deep interior of Earth.”

Answering the questionsMagnetic field

•While some other generation processes have been argued, our only tenable model for field generation at present is a self-exciting magneto-hydrodynamic dynamo.

•Given a pre-existing magnetic field, electrical currents are generated in a conductor (the fluid of the “iron” outer core) moving (why?) through it.

•The magnetic field necessarily associated to these currents becomes aligned with pre-existing field due to coriolis forces within the core due to Earth's spin!

Glatzmeir and Olson showed that this process could generate a field that “looks like” Earth's using computer models of the magneto-hydrodynamics of the outer core within the spinning Earth.

Answering the questionsAge, formation, composition

Age? Tight at 4.567Ga... if Earth formed coincident with age-determined meteorites! … but

Formation? Ever more new models are still being proposed and discounted!

Composition? Modelled on Estatite chondrites? Fashionable but it doesn't explain Fe!

Answering the questionsInterior Mineralogy and Temperature Profile

References:

• Ho-kwang Mao and Russell J. Hemley• Kei Hirose