Prescott College — For the Liberal Arts, the Environment & Social Justice Critical Review: Is Earth's Outer Core Liquid or a High Density Plasma? Daniel S. Helman Sustainability Education, Prescott College, 220 Grove Ave., Prescott, AZ 86301 danielhelmanteaching@yahoo.com Abstract This work explores composition and melting point data (or lack of data) related to Earth's outer core, and also the possibility of a high-density plasma composition, plus gives a background on Inge Lehmann's seismological observation demonstrating a solid inner core. Implications related to geomagnetic field dynamics are also presented, as are evidence in the rock record for changes to the geomagnetic field over time, including the intersection (if any) of such changes and the origin and development of life on the planet. Keywords geodynamo, plasma, metallic liquid, solid-density plasma, plasma channel, origin of life, geomagnetic field Inner and Outer: How Do We Know? Here are the words of Inge Lehmann, who made this discovery: Evidently, there was a reflection of the waves in the interior of the earth that caused them to emerge at a shorter epicentral distance. It was shown in a simple example how this could happen. I considered a globe in which a hard mantle surrounded a softer core, the radius of which I took to be five ninths of the surrounding sphere. The velocity of the longitudinal waves was 10 km/s in the mantle and 8 km/s in the core. It was then a simple matter to calculate the time curves arising from an earthquake that took place at the surface of the globe. The P curve that resulted from waves confined to the mantle ended at 112° distance from the epicenter. P' consisted of two brances, as observed in the New Zealand earthquake. When the variation of the travel time was considered in relation to the angle of incidence, an estimate of the intensity could be obtained. In this way it was found that the intensity of the waves corresponding to the upper branch of the P' curve would be small. This was in accordance with the fact that it had been difficult to observe the upper branch. No rays emerged at epicentral distances between 112° and 154° (Figure 6). I then placed a smaller core inside the first core and let the velocity in it be larger so that a reflection would occur when the rays through the larger core met it. After a choice of velocities in the inner core was made, a time curve was obtained (Figure 7), part of which appeared in the interval where there had not been any rays before. The existence of a small solid core in the innermost part of the earth was seen to result in waves emerging at distances where it had not been possible to predict their presence. Gutenberg accepted the idea. He and Charles Richter (California Institute of Technology, Pasadena) placed a small core inside the earth and adjusted the radius of this small core until the calculated time curves agreed with the waves observed. Jeffreys was slower to accept the inner core. Jeffreys- Bullen time curves had been completed in 1935. In 1939, a new edition was published in which the inner core had been accepted. ... Inge Lehmann was born in 1888 and received her degree in mathematics in 1920. She later became chief of the Seismological Department of the Geodetic Institute of Denmark, which was established in 1928. As described in this article, she aided in setting up seismic stations in Greenland and Copenhagen. Her studies of the travel times of a special phase led to the discovery of the inner core of the earth in 1936. [1] Is the Outer Core a Liquid or a Plasma? Consider the following quote in light of how a plasma is defined: “The best hard sphere model for the core is a transition metal liquid whose valence electrons form an electron sea bathing and charge-compensating the spherical ionic cores.” [2] The term metallic (or metal) liquid also appears in text related to the core of Jupoter: “Jupiter's magnetic field is caused by convective dynamo motion of electrica