Bruce Buffett on Probing the Earth’s Core
Bruce Buffett is a Professor in the Department of Earth and Planetary Science at the University of California, Berkeley. He investigates the structure and motions within the Earth’s core by matching physics-based simulations of the core to the observed magnetic field of the Earth.
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Podcast Illustrations
Diagrammatic cross-section of the Earth showing the very thin crust, the mantle (orange) and the core, with a solid inner part and a liquid outer part.
Courtesy of Eric King
Artist’s impression of two of the three ESA Swarm satellites which have been surveying the Earth’s magnetic field since 2014. Each satellite has two magnetometers. One sits on the end of the boom and measures the absolute magnitude of the field. The other is located about halfway down the boom and measures each of the x, y, and z components of the magnetic field. Bruce Buffett is using Swarm measurements of the 10-60-year period variations in the Earth’s magnetic field to improve our understanding of the core. He thinks these variations might be caused by physical wave motions in a layer of the outer core.
Courtesy of ESA
An iron meteorite composed of an iron-nickel alloy, similar in composition to that of the Earth’s core. Such meteorites originated from the cores of planetesimals - small bodies formed during the process of planet formation. This example shows Widmanstätten patterns, whose shapes are caused by long iron-nickel crystals.
Courtesy of H. Raab
Computer simulations of the Earth’s liquid outer core generated by numerically integrating the equations of fluid motion (Navier-Stokes equations) and electromagnetism (Maxwell’s equations). The colors indicate the radial velocity of the core material on the plane of the Equator. The two calculations differ in the assumed value of the core viscosity. The simulation on the right assumes a viscosity 500 times smaller than that on the left (corresponding to the viscosity of asphalt) but that is still many orders of magnitude higher than the actual viscosity of the core. The calculation gets more compute-intensive as the viscosity is reduced, but it becomes more realistic.
Courtesy of Bruce Buffett
Higher-resolution image of the results of the simulation at top right. The broad features, such as the scale of the plumes around the inner core (the black disc) and the outwardly decreasing scale of the motions, are thought to represent the actual core correctly, but a simulation that uses a lower viscosity (closer to that of water) would show much smaller scale structures. Nonetheless, the broad features seen in existing simulations can explain the observed magnetic field.
Simulation of the radial magnetic field at the core-mantle boundary. The overall structure is that of a dipole (yellow in Northern Hemisphere, and blue in the Southern Hemisphere) but there are also smaller-scale features. It is the small-scale structure that disappears when the stratified layer at the top of the core gets too thick. The simulation shows a slight weakening of the magnetic field at the North Pole. This is probably a transient feature, but it may reflect the present-day field at the core-mantle boundary since the field at the North Pole is, in fact, quite weak. This simulation uses a viscosity value intermediate between those used in the two simulations shown above.
Courtesy of Bruce Buffett