New Technique Could Reveal High Detail Of Earth's Composition
February 22, 2013

New Technique Could Reveal High Detail Of Earth’s Composition

April Flowers for - Your Universe Online

In a new study recently published in the journal Science, a research team from Amherst College and The University of Texas at Austin has described a new technique that might one day reveal the composition and characteristics of the deep Earth in never before seen detail.

There's just a tiny little hitch in the new technique. It relies on a fifth force of nature that has not yet been detected. Current physics theories hold that there are four forces; strong and weak, which have to do with subatomic particles, gravity and electromagnetic. Some particle physicists, however, think a fifth force might exist. They call this type of force a long-range spin-spin interaction. This exotic new force, if it exists, would connect matter at Earth's surface with matter deep in the mantle, hundreds or even thousands of miles below.

To put it another way, the building blocks of atoms — electrons, protons and neutrons — would "feel" each other's presence though separated by vast distances. The interaction of these particles could provide scientists with new information about the composition and characteristics of the mantle, which is poorly understood because of its inaccessibility.

"The most rewarding and surprising thing about this project was realizing that particle physics could actually be used to study the deep Earth," Jung-Fu "Afu" Lin, associate professor at The University of Texas at Austin's Jackson School of Geosciences, said in a statement.

Proving the existence of this new force could help settle a scientific quandary. Earth scientists have tried to model how factors such as iron concentration and physical and chemical properties of matter vary with depth. For example, they use the way an earthquake rumbles through the Earth, or laboratory experiments designed to mimic the intense temperatures and pressures of the deep Earth. The problem is, they get different answers. The fifth force might help to reconcile conflicting lines of evidence.

Made up mostly of iron-bearing minerals, Earth's mantle is a thick geological layer sandwiched between the thin outer crust and central core. The subatomic particles of the atoms, and the atoms themselves, making up the minerals in the mantle have a property called spin, which can be thought of as an arrow pointing in a particular direction. Some earth scientists believe that Earth's magnetic field causes some of the electrons in these mantle minerals to become slightly spin-polarized. This means the direction in which they spin is no longer completely random, but has some preferred orientation. These polarized electrons have been dubbed geoelectrons.

The goal of this study was to see if the researchers could use the proposed long-range spin-spin interaction to detect these geoelectrons.

Larry Hunter, professor of physics at Amherst College, led the research group as they first created a computer model of Earth's interior -- based in part on insights gained from Lin's laboratory experiments that measure electron spins in minerals at the high temperatures and pressures of Earth's interior -- to map the expected densities and spin directions of geoelectrons. The map provided clues about the strength and orientations of interactions the research team might expect to detect in their specific laboratory location in Amherst, Mass.

Then the team used a specially designed tool to search for interactions between geoelectrons deep in the mantle and subatomic particles at Earth's surface, essentially exploring whether the spins of electrons, neutrons or protons in various labs might have a different energy, depending on the direction, with respect to the Earth, that they were pointing.

"We know, for example, that a magnet has a lower energy when it is oriented parallel to the geomagnetic field and it lines up with this particular direction – that is how a compass works," explains Hunter. "Our experiments removed this magnetic interaction and looked to see if there might be some other interaction with our experimental spins. One interpretation of this 'other' interaction is that it could be a long-range interaction between the spins in our apparatus and the electron spins within the Earth, that have been aligned by the geomagnetic field. This is the long-range spin-spin interaction we were looking for."

The apparatus was not able to determine any such interactions, leading the team to infer that such interactions, if they exist, are incredibly weak -- no more than a millionth of the strength of the gravitational attraction between the particles. The scientists consider this important information useful as they look for ways to build even more sensitive instruments to search for this elusive fifth force.

"No one had previously thought about the possible interactions that might occur between the Earth's spin-polarized electrons and precision laboratory spin-measurements," says Hunter.

"If the long-range spin-spin interactions are discovered in future experiments, geoscientists can eventually use such information to reliably understand the geochemistry and geophysics of the planet's interior," says Lin.