Graduate Student Welcome Week September 9, 2015 Introduction – Olivia Jensen

about Olivia… Born… in the deep winter of 1943 in a farmhouse in Springbank, AlbertaBorn… in the deep winter of 1943 in a farmhouse in Springbank, Alberta Educated… in the public schools of Calgary, Vancouver and at the University of BCEducated… in the public schools of Calgary, Vancouver and at the University of BC Joined McGill’s Faculty of Engineering in 1973 and then Faculty of Science in 1984Joined McGill’s Faculty of Engineering in 1973 and then Faculty of Science in 1984 Married: 1975 – son of 34, daughter of 32, both McGill graduates; grandson 6, granddaughter 3Married: 1975 – son of 34, daughter of 32, both McGill graduates; grandson 6, granddaughter 3 Divorced: 1989Divorced: 1989 “Transition”: 1989 with some following medical interventions“Transition”: 1989 with some following medical interventions

Questioning the Faith Elements of faith in geology and geophysics Uniformitarianism Layered structure Magnetic field generation Interior rheology Age, formation, composition Interior mineralogy and temperature

Answering the questions Principle of Uniformitarianism Generalized covariance is inherent to the two great theories upon which our physics is constructed: Quantum Mechanics Gravitation (General Relativity) These two theories are thought to be only insufficient to describe nature before seconds following the Big Bang. They have, so-far, failed no empirical tests. Geological and geophysical processes since BB s follow the “laws” of physics... hence PofU?

Answering the questions Layered Structure Seismology finds global radial variations in physical properties α and β at many nearly fixed depths within the Earth. ~5-70 km 410 km 660 km ~2700 km ± 2890 km 5150 km

Answering the questions Interior 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: e shear = (t/2η + 1/2μ) σ shear

Answering the questions Magnetic 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 questions Age, 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!discounted Composition? Modelled on Estatite chondrites? Fashionable but it doesn't explain Fe!Modelled

Answering the questions Interior Mineralogy and Temperature Profile References: Ho-kwang Mao and Russell J. Hemley Kei Hirose