CNN - July 1996

Deep inside the Earth, spinning in a watery pool of iron, the Earth's core is a giant iron crystal slightly smaller but more dense than the moon. Beyond that, the substance at the heart of our planet always has been a mystery.

Although seismologist Xiaodong Song acknowledged the mystery is "really a complicated problem," he and fellow seismologist Paul Richards have managed to unravel it.

They announced that their relatively superficial study of 28 years' worth of earthquake records at the Lamont-Doherty Earth Observatory shows the core is in motion, and going at a pretty good clip.

The Columbia scientists measured the underground effects of earthquakes, determining how quickly their movement travels through the center of the Earth to other places on the globe.

The scientists have learned that the Earth's core is turning in an eastward direction and spinning faster than the Earth itself. Every 400 years, the core is a full turn ahead of the Earth.

"The really surprising thing is how fast the core is moving," Richards said. They estimate the core moves about 100,000 times faster than the movements of the Earth's tectonic plates.

This information about the Earth's core may shed new light on how the Earth works. For starters, the core's motion could help explain why magnetic north and south periodically wander or reverse over Earth's history.

"This rotation that has been found allows us to go forward in understanding the Earth's magnetic field. So we think we understand it better than we did before this observation," seismologist Paul Silver said.

Gravitational pull and seismic activity also could be viewed differently because of this discovery.

There's a giant crystal buried deep within the Earth, at the very center, more than 3,000 miles down. It may sound like the latest fantasy adventure game or a new Indiana Jones movie, but it happens to be what scientists discovered in 1995 with a sophisticated computer model of Earth's inner core. This remarkable finding, which offers plausible solutions to some perplexing geophysical puzzles, is transforming what Earth scientists think about the most remote part of our planet.

"To understand what's deep in the Earth is a great challenge," says geophysicist Lars Stixrude. "Drill holes go down only 12 kilometers, about 0.2 percent of the Earth's radius. Most of the planet is totally inaccessible to direct observation." What scientists have pieced together comes primarily from seismic data. When shock waves from earthquakes ripple through the planet, they are detected by sensitive instruments at many locations on the surface. The record of these vibrations reveals variations in their path and speed to scientists who can then draw inferences about the planet's inner structure. This work has added much knowledge over the last ten years, including a puzzling observation: Seismic waves travel faster north-south than east-west, about four seconds faster pole-to-pole than through the equator.

This finding, confirmed only within the past two years, quickly led to the conclusion that Earth's solid-iron inner core is "anisotropic" -- it has a directional quality, a texture similar to the grain in wood, that allows sound waves to go faster when they travel in a certain direction. What, exactly, is the nature of this inner-core texture? To this question, the seismic data responds with sphinx-like silence. "The problem," says Ronald Cohen of the Carnegie Institution of Washington, "is then we're stymied. We know there's some kind of structure, the data tells us that, but we don't know what it is. If we knew the sound velocities in iron at the pressure and temperature of the inner core, we could get somewhere." To remedy this lack of information, Stixrude and Cohen turned to the CRAY C90 at Pittsburgh Supercomputing Center.

Earth's layered structure -- a relatively thin crust of mobile plates, a solid mantle with gradual overturning movement, and the outer and inner core of molten and solid iron.

Don't believe Jules Verne. The center of the Earth is not a nice place to visit, unless you like hanging out in a blast furnace. The outer core of the Earth, about two-thirds of the way to the center, is molten iron. Deeper yet, at the inner core, the pressure is so great - 3.5 million times surface pressure -- that iron solidifies, even though the temperature is believed to exceed 11,000 degrees Fahrenheit, hotter than the surface of the sun.

Despite rapid advances in high-pressure laboratory techniques, it's not yet possible to duplicate these conditions experimentally, and until Stixrude and Cohen's work, scientists could at best make educated guesses about iron's atom-to-atom architecture - its crystal structure - at the extremes that prevail in the inner core. Using a quantum-based approach called density-functional theory, Stixrude and Cohen set out to do better than an educated guess. With recent improvements in numerical techniques, density-functional theory had predicted iron's properties at low pressure with high accuracy, leading the researchers to believe that with supercomputing they could, in effect, reach 3,000 miles down into the inner core and pull out what they needed.

Three crystal structures of iron.
Yellow lines show bonds between iron atoms.

Rethinking Inner Earth

On Earth's surface, iron comes in three flavors, standard crystalline forms known to scientists as body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp). Working with these three structures as their only input, Stixrude and Cohen carried out an extensive study - more than 200 separate calculations over two years - to determine iron's quantum-mechanical properties over a range of high pressures. "Without access to the C90," says Stixrude, "this work would have taken so long it wouldn't have been done."

Prevalent opinion before these calculations held that iron's crystal structure in the inner core was bcc. To the contrary, the calculations showed, bcc iron is unstable at high pressure and not likely to exist in the inner core. For the other two candidates, fcc and hcp, Stixrude and Cohen found that both can exist at high pressure and both would be directional (anisotropic) in how they transmit sound. Hcp iron, however, gives a better fit with the seismic data. All this was new information, but even more surprising was this: To fit the observed anisotropy, the grain-like texture of the inner core had to be much more pronounced than previously thought.

"Hexagonal crystals have a unique directionality," says Stixrude, "which must be aligned and oriented with Earth's spin axis for every crystal in the inner core." This led Stixrude and Cohen to try a computational experiment. If all the crystals must point in the same direction, why not one big crystal? The results, published in Science, offer the simplest, most convincing explanation yet put forward for the observed seismic data and have stirred new thinking about the inner core.

Could an iron ball 1,500 miles across be a single crystal? Unheard of until this work, the idea has prompted realization that the temperature-pressure extremes of the inner core offer ideal conditions for crystal growth. Several high-pressure laboratories have experiments planned to test these results. A strongly oriented inner core could also explain anomalies of Earth's magnetic field, such as tilted field lines near the equator. "To do these esoteric quantum calculations," says Stixrude, "solutions which you can get only with a supercomputer, and get results you can compare directly with messy observations of nature and help explain them -- this has been very exciting."

- By Hoyt Coffee

Jules Verne sent an intrepid band of adventurers on a Journey to the Center of the Earth, where they discovered vast unknown lands, great oceans and lost civilizations. Of course, modern science long ago dispelled such outlandish if entertaining notions, but researchers today are making real scientific discoveries about the earth's core seemingly no less fantastic than Verne's imaginings.

Seeking to explain the unusual behavior of seismic waves generated by earthquakes and the mysteries of the earth's magnetic field, two scientists have found evidence that the answers may lie at the very core of the planet - in a single giant crystal.

"Seismologists found that the waves produced by earthquakes travel faster when they travel along the north-south pole of the earth than they do in the equatorial plane. And what we wanted to do was to understand what causes this observation," says Dr. Lars Stixrude, assistant professor of earth and atmospheric sciences in Georgia Tech's College of Sciences. "One possibility is that the earth's core is, in fact, a single crystal of iron."

As the earth was being formed from the remnants of exploding stars billions of years ago, most of the iron in this fiery soup sank into its deep interior. There it was crushed, at pressures more than 3 million times greater than those found at the surface, into an iron sphere some 1,500 miles in diameter. That inner core, which remains a solid despite temperatures believed to exceed 7,000 degrees Fahrenheit, was long thought a featureless ball of matter having little or no effect on the planet.

Knowing that seismic waves took about four fewer seconds to traverse the planet through the poles, Stixrude and his colleague, Dr. Ronald E. Cohen, a geophysicist at the Carnegie Institution of Washington, created a computer model of the earth's core. The model utilized Density Functional Theory, which uses mathematics to mimic the atomic structure of a material. Working with a Cray computer at the Pittsburgh Supercomputing Center, they compared the effect of passing seismic waves through the computer with that observed in nature.

"What we did was to use some quantum-mechanical calculations to predict the properties of iron at the very high pressures and temperatures that exist in the center of our planet," says Stixrude, whose interest in earth sciences carried him from high-school geology to a doctorate at the University of California, Berkeley. "We predicted, based on the calculations, that the inner core was made of a hexagonal structure of iron and that the elastic properties of the inner core are similar to those of a single crystal of iron."

A hexagonal crystal, one of the three known structures iron can take, is different from the cubic crystalline structures iron takes at the planet's surface. Its "anisotropy" - its tendency to let waves pass through it more easily in a certain direction - may explain why the tiny inner core can have such a large effect on seismic waves and on the earth's magnetic field.

"The earth's core is actually composed of two parts: There's the solid inner core, and surrounding that is a liquid outer core," Stixrude says. "It's that liquid outer core where the magnetic field is produced." While the 4,300-mile-wide outer core may produce the magnetic field, the hard center may modify it in important ways.

"To a very good approximation, the earth's field has the same shape that a bar magnet's has: It's a dipole field, but there are very slight deviations from that shape that the earth's magnetic field shows," Stixrude says. That shape, something like an apple sliced downward through its core, would be constant for a bar magnet. But in the earth's case, the lines connecting the north and south poles are skewed at the equator, where they should be parallel, in what's termed an inclination anomaly.

"This is a well-documented observation that people have known for a long time but haven't been able to explain," Stixrude says. "We suggested that one possible explanation was that the inner core might have an influence on the production of the magnetic field, might guide the production of the field somehow, might modify it somehow so as to produce this skewing of the field lines."

Stixrude and Brad Clement of Florida International University believe the inner core may also have something to do with a much more dramatic fluctuation of the magnetic field. About every million years or so, the field reverses polarity: the north and south poles switch position. Paleomagnetists, who study the effect of the magnetic field in the geologic record, discovered this phenomenon while studying the crystalline structure of rocks. As the rocks cool from lava, for instance at the deep mid-ocean ridges where the earth's surface plates are formed, crystals line up with the direction of the magnetic field. Once completely cooled, the rocks retain their orientation and are no longer susceptible to magnetism.

By dating the rocks and noting their crystalline structure, paleomagnetists can tell which direction the magnetic field took at any given time. They say evidence shows the last reversal occurred about 700,000 years ago.

"We talked about the possible influence of the inner core on this process of how the field reverses. We know it reverses; it reverses throughout geologic history. We don't exactly know why, but we've been discovering more and more recently about just how it does it," he says. The reversal takes a relatively short amount of time, geologically speaking, only a few thousand years. And during the transition, the field retains its dipole shape, a phenomenon paleomagnetists have traced all the way to the south pole.

"What's interesting about that process is that the path that the north pole takes during this reversal seems to follow two preferred paths: one through the Americas and one through eastern Asia," Stixrude says. The researchers theorize that as the poles shift, the main field produced in the outer molten core weakens, becoming more susceptible to the influence of the inner core.

The magnetic field also varies on a century time scale, never aligning exactly with the geographic north pole. It currently is centered about 12 degrees away from the geographic north pole. "There are always fluctuations. And if you look at how much the field has changed, even over just the last few centuries, you'll find that it moves around quite a lot," Stixrude says.

So, why is it important to know how the earth's inner core affects magnetic fields?

"We know that most of the planets have magnetic fields, and stars all have magnetic fields. If we understood better how magnetic fields were produced, we could understand more about the deep interior, where this production is going on. And that's something we hope to use it for, not only to understand the magnetic field itself, which is really interesting, but to understand more about the interior, too."

Metaphysics -

Planet Earth supposedly has a core crystal in the center of the Earth - beneath the Great Pyramid - the major grid point - center - of planet Earth. It functions much the same way as a central computer. It is was programmed by Tehuti - or Thoth - after the Atlantean Program ended and the Egyptian Program began.

This is the supposedly the master crystal which set up the planetary grids that create our reality. The grids hold all of the history of the program in which we experience. We sometimes refer to this crystal as the Hall of Records - the Akashic Records - or the collective unconsciousness. Some people believe it exists in another frequency.