Introduction Olivia Jensen Graduate Student Welcome Week September

Introduction – Olivia Jensen Graduate Student Welcome Week September, 2017

about Olivia… • Born… 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 BC • Joined Mc. Gill’s Faculty of Engineering in 1973 and then Faculty of Science in 1984 • Married: 1975 – son of 37, daughter of 35, both Mc. Gill graduates; grandson 9, granddaughters 6 and 1. • Divorced: 1989 • “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 10 -33 seconds following the Big Bang. They have, so-far, failed no empirical tests. Geological and geophysical processes since BB+1033 s follow the “laws” of physics. . . hence Pof. U?

Answering the questions Layered Structure • Seismology finds global radial variations in physical properties α (P-wave speed) and β (S-wave speed) 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 = (t/2η + 1/2μ)σ shear

Seismic provisos Seismic 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 questions Magnetic field • While some other generation processes have been argued, our only tenable model for field generation at Glatzmeir and Olson showed present is a self-exciting magneto-hydrodynamic dynamo. that this process could generate a field that “looks like” • Given a pre-existing magnetic field, electrical currents are generated in a conductor (the fluid of themodels “iron” Earth's using computer outer core) moving (why? ) through it. of the magneto-hydrodynamics • The magnetic field necessarily of the outerassociated core withinto thethese currents becomes aligned with Earth. pre-existing field due spinning to coriolis forces within the core due to Earth's spin!

Answering the questions Age, formation, composition • Age? Tight at 4. 567 Ga. . . if Earth formed • • coincident with age-determined meteorites! … but Formation? Ever more new models are still being proposed and discounted! Composition? Modelled on Enstatite chondrites? Fashionable but it doesn't fully explain Fe!

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