Fri December 16, 2011
Dr. Michael Bergman, Bard College at Simon's Rock - The Earth's Core
Albany, NY – In today's Academic Minute, Dr. Michael Bergman of Bard College at Simon's Rock describes one of the Earth's most extreme environments, its inner core.
Michael Bergman is a professor of physics at Bard College at Simon's Rock where his research interests include geophysical fluid dynamics. Bergman is conducting studies on the effects of rotation and magnetic fields on the convection that results from the solidification of the Earth's core. He holds a Ph.D. from the Massachusetts Institute of Technology.
Dr. Michael Bergman - The Earth's Core
Let's take a quick Journey to the Center of the Earth, a place even more bizarre than the one Jules Verne imagined in 1864. The Earth's solid iron inner core is so remote it was not discovered until 1936 by Danish seismologist Inge Lehmann. At 3 million times atmospheric pressure and nearly 10,000 degrees Fahrenheit it is a most inhospitable place. Most of what we know comes from seismology. Whenever there is a big earthquake seismic waves travel through the Earth and are recorded by seismometers around the globe. By the speed, size, and shape of the waves, seismologists can infer properties of the materials the waves travel through, much like a CATSCAN.
Over the past twenty years seismologists have found that waves traveling north-south in the inner core are faster than those traveling east-west. This tells us something about the aligning of the iron crystals in the inner core. We study how metals solidify and deform -- processes that can cause crystals to align. Based on our experiments we have suggested that the solidifying iron crystals are recording the flow pattern of the molten iron outer core. Seismologists have also inferred that the inner core is super-rotating. In other words, the rotation rate of the inner core is faster than the mantle, so it laps the surface in some few thousand years.
Recently, geophysicists suggested that the inner core may also be translating. As the Earth cools and the solid inner core grows slowly outwards, it moves from west to east, melting on one side and solidifying on the other, keeping the inner core at the center. This recycling means that although there has been an inner core for perhaps a billion of the Earth's 5 billion years, any solids present today may not be more than a few hundred million years old, like the Phoenix of mythology.