Special K discovery might reveal details of Earth's core

By MICHAEL LEACH
Collegian Science Writer

Scientists may not have to journey to the center of the Earth to gain a better understanding of its composition thanks to a recent discovery concerning the behavior of potassium under high pressure and temperature.

Simulating those conditions in the lab has given University scientists insight into what the behavior of potassium might be like thousands of miles below the Earth's crust. John Badding, associate professor of chemistry, has been exploring the behavior of potassium under conditions similar to those far below the Earth's crust. By producing the high pressures and temperatures associated with the Earth's core, Badding has discovered a marked change in the behavior of potassium - that it behaves like a transition metal.

- Russell Hemley, a staff scientist at the Geophysical Lab of the Carnegie Institute in Washington, D.C.

"Basically, we took potassium, which undergoes an electron transition under pressure, and put it in a diamond anvil cell, a high-pressure apparatus, and put it in the presence of nickel powder and pressurized it," Parker said. "And then we found that a compound was formed."

The outer electron of potassium normally orbits the nucleus in a spherical configuration known as an s-orbital. However, that electron configuration can change under stressful conditions.

Potassium was placed along with nickel powder into a diamond anvil cell, which applied a pressure of 310,000 times normal atmospheric pressure and a temperature of 4,000 degrees Fahrenheit.

Under the intense heat and pressure of the diamond anvil cell, the electron configuration of potassium buckled and the volume of the electron cloud shrunk by a factor of four to form a more compact d-orbital. The formation of the new orbital allowed the potassium to behave like the transition metals, elements whose outermost electrons reside in d-orbital configurations under normal conditions.

It was this new behavior that caused potassium to react with nickel, forming a new compound, Parker said.

Russell Hemley, a staff scientist at the Geophysical Lab of the Carnegie Institute in Washington, D.C., and former colleague of Badding, said the recent discovery is significant from several different standpoints.

"From the standpoint of fundamental chemistry it is interesting because it shows that there is a chemistry of the elements that can be very different at high pressure," Hemley said.

"It is also interesting from the standpoint of Earth science because it proposes that potassium may be a heat source localized within the core of the Earth. What this discovery points out is that it is possible that the chemistry of what they found in potassium may allow potassium to be incorporated in the iron core of the Earth."

Badding's team plans to continue working with potassium to discover the properties of the nickel-potassium compound. Afterwards, the team will explore the reactivity of potassium with iron under high-pressure conditions.

"We want to investigate the structures of the materials we've made and move on over toward iron," Badding said.

After working out the properties of potassium-transition metal compounds, Badding plans to perform similar experiments with other alkali metals such as rubidium and possibly cesium to explore the possibility of the presence of other alkali metals in the Earth's core.

"Understanding the composition of the Earth is a fundamental question that goes back many, many centuries so it is something of which we would like to have a very detailed understanding," Hemley said. "In the case of the core, the core is the most remote part of the Earth's interior. An understanding of the chemistry of the composition of the core of the Earth has important implications for the magnetic field of the Earth and other important global geophysical properties."