Cooler at the Core

Though scientists are solving more and more of the mysteries in the sky above, they still know surprisingly few of the secrets hidden in the earth be low. But now, combining sharp observation and shrewd reasoning, U.C.L.A.

Professor George Kennedy has cut in half previous estimates of the tempera ture of the earth's core. His cool calculations promise new insight into both the current structure of the earth and ancient geologic activity.

In determining melting points of iron (and all other substances that increase in volume as they melt), scientists have long used Lindemann's Law, a complicated mathematical formula describing the relationship between the melting temperature of a substance and the pressure upon it. But Geologist Kennedy was disturbed by the widely varying and apparently inaccurate results obtained when the law was applied at higher pressures. He decided that something was wrong.

Using data from carefully controlled laboratory tests, he plotted the melting temperatures of some 50 different sub stances against their density at varying pressures. The graphs that resulted clearly confirmed his suspicions: there is a direct relationship between melting point and density, not melting point and pressure.

After writing a simple formula to ex press this relationship, Kennedy applied it first to a determination of the temper ature in the earth's core --until now calculated by extrapolation of Lindemann's Law to be 13,500DEG F. Instead of the estimated pressure at the earth's inner core (3,000,000 atmospheres), he used the experimentally derived density of iron at this pressure --about twice its density at sea level. Putting that figure into his formula, he arrived at a new and more realistic estimate of the heat in the earth's iron core: only 6,700DEG F.

Kennedy's findings should alter most theories about the thermal history of the earth, and help scientists learn more about how heat escapes from the earth's interior. In addition, the formula final ly establishes a correct relationship be tween a substance in its solid and liquid states, besides offering a new approach to studies of the melting process. In retrospect, Kennedy's discovery might seem obvious, but the startling truth is that generations of scientists overlooked it. "The profession must be full of asses," says Nobel Prize Chemist Willard Libby, discoverer of the carbon-14 dating process. "How can anyone be so stupid as not to have seen it?"

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