John Baumgardner, a geophysicist from nearby Los Alamos National Laboratory, sees such wonders daily, an experience that drives him to study a simulated Earth on his office computer screen. There, Baumgardner can watch the planet take shape through sometimes violent forces and search for ways of predicting the earthquakes that still strike today.

"I am fascinated with how the Earth came to be the way it is and by the evidence that dramatic geological processes have operated in the past," says Baumgardner, who uses supercomputers to explore motions deep inside the Earth. "For most of the century, however, there has been a disconnect between the geophysicists studying these processes and the geologists studying the detailed features in the rocks."

Photo William Mercer McLeod

Visualizing supercomputer output helps John Baumgardner reconstruct 120 million years of temperature changes in the Earth’s middle layer -- the mantle. (large)

The dilemma hinges on an inability to get very far inside the planet to watch even the present-day motions. The deepest drill hole, for instance, reaches merely eight miles down.

A supercomputer, by contrast, can drill all the way through at several million points simultaneously. Mathematical equations represent the physics along the drill holes. Following changes over time, supercomputer simulations provide a fast-forward version of the evolving Earth to check against and
fill out the hazy picture painted by observations.

"Simulations have the potential to bridge the gap between geologists
and geophysicists while explaining how the geological structures actually came about," Baumgardner says.

Three years ago, he joined a NASA-funded research team boring through the Earth with simulation. By exposing interactions between the planet's three primary layers -- the crust, mantle and core -- they are gaining insights into problems ranging from continental drift to reversals of the north and south magnetic poles.

A patchwork of plates

Most responsible for surface geology are tectonic plates. These 50-mile-thick slabs of rock include the top layer (the crust of the continents and ocean floor) and the uppermost part of the middle layer (the 1,800-mile-thick shell of denser rock that comprises the mantle).

Plate movements carried the continents to their present-day positions. They split what is now New Mexico, dragging up hot mantle material in a volcanic eruption 500 times larger than that of Mount St. Helens. Plate collisions built mountain ranges such as the Himalayas. Today, as plates slip past each other, we get earthquakes.

Tectonic plates cover the Earth like a giant patchwork. Much of the plates’ geological work occurs when they sink into the mantle, as they do today around the rim of the Pacific Ocean. Mantle specialist Baumgardner says, "We've been working hard to improve the plate representation during the last three years under NASA funding." He considers this progress their most exciting achievement.

Plates behave as brittle solids at the planet surface but become soft and plastic as they dive into the pressure cooker of the mantle. "Representing accurately how rock deforms under extreme conditions is crucial to the fidelity of our simulations," Baumgardner says.

With some plate physics in hand, Princeton University's Hans-Peter Bunge, Baumgardner and collaborators are busy reconstructing a history of mantle and tectonic plate motions. It goes back 120 million years in geological time.

One visualized simulation image looks like a multicolored ball with a section cut out. The ball faces the Pacific Ocean hemisphere, and the cutout portion lies to the northwest. The colors represent temperatures. They range from blue for cold, about 50 degrees Fahrenheit, to red for hot, about 5,000 degrees Fahrenheit.

By tracking how the colors change with time, the team learns how rock and heat move through the planet. The ball’s surface is entirely blue and green because the rock is cool there. In the cutout, where these surface colors extend downwards, cool rock is sinking into the mantle. Red, orange and yellow regions are where mixing occurs. The red surface at the center indicates the top of the outer core.

Tectonic plates, whose boundaries are traced as white lines on the surface, move and change shape during the simulation. At the end, plate movements have produced a more complex sinking pattern under the northwestern Pacific Ocean crust, as visualized in a second snapshot inside the Earth.

Including plate information is helping the group recover the current pattern of hot and cold regions inside the mantle. "We get the complete anatomy of the Earth's interior with simulation," says NASA research leader Peter Olson, professor of geophysical fluid dynamics at Johns Hopkins University. "Motion is everywhere inside the Earth. There is no way to get that information from observations alone."

Once they can resolve the past, "simulations will tell us what is going to happen next," Olson adds. Baumgardner is exploring the possibilities now, albeit on a regional scale.

John Baumgardner is applying his mantle and tectonic plate knowledge to a San Francisco Bay earthquake simulation project.

He coordinates with the University of California, Berkeley, on a San Francisco Bay Area earthquake simulation project. The software concept includes the crust, upper mantle and a network of faults. A reality check comes from 28 Global Positioning System satellite stations, which constantly monitor the region. The group seeks agreement between normally slow ground deformations captured by the satellites and those in the simulations.

Then, "once all the pieces are in place, we plan to look for unusual changes in the deformation pattern that might signal increased slippage on a fault, interrogate our simulation to try to identify that fault and be able, hopefully, to predict earthquakes in the Bay Area," Baumgardner says. "That's definitely an optimistic goal, but we believe the technology is now available to at least test the feasibility of the concept."

Magnetic gymnastics

Drilling 1,800 miles down, the simulations reach the Earth's innermost region, the core. Scientists have some notion of its structure mainly from recording sound waves that reverberate throughout the planet following earthquakes. Recent probings show a solid iron ball (inner core) spinning in a boiling cauldron of molten iron (outer core).

While the core is alien and remote, anyone who uses a compass gets information from this realm. Being a metal, the core conducts electricity. The outer core’s twisting and shearing motions act as an electric generator that in turn produces the magnetic field that gives the Earth north and south poles.

The NASA team has found the core's behavior partly arises from an intriguing relationship with the mantle. "The core is more or less the slave of the mantle," Olson says.

Mantle rock motion is about one million times slower than the motions of the outer core. Sinking, cold mantle material spreads into blobs when it reaches the core and shoves aside hot material at the boundary. The resulting cold patches, which remain for hundreds of millions of years, pull heat more rapidly from the core and seem to affect the magnetic field’s evolution.

This uneven heat exchange has features too small for current supercomputers to mimic when treating the whole globe, so Olson uses simulation of a different sort. He builds a "core" in his Johns Hopkins laboratory.

The scale-model takes a metal bowl, about the size for serving salad, as the outer core's southern hemisphere (the northern half is presumably the same). With an attached shaft, postdoc Ikuro Sumita spins the bowl at 250 revolutions per minute to approximate the Earth's rotation and gravity. Wires inject appropriate hot and cold patterns from the mantle and inner core.

As the apparatus revs up, green-dyed water portraying molten iron rolls around inside the bowl. A parade of spirals soon join in a pinwheel. Eventually, the dye drifts westward. Olson smiles because observations show the Earth's magnetic field does that. Likewise, temperature probes on the bowl confirm a measured large heat loss around the Pacific Ocean.

The green water may reproduce the flow, but it has no magnetic properties. For understanding the Earth's dynamic magnetic field, the team returns to a supercomputer.

University of California colleagues Gary Glatzmaier (Santa Cruz) and Paul Roberts (Los Angeles) have developed software to simulate the core and the magnetic field from its origin out to interplanetary space. "The problem is so complicated that we can’t even guess what the solution would be," says Glatzmaier, professor of Earth sciences at Santa Cruz. "The magnetic field evolves, and it affects the fluid flow, and the fluid flow affects the magnetic field and the temperature and densities. They all affect everything else, every 15-day numerical time step of the simulation.”

"So you have something that's almost alive and sitting there," he adds. "You've created it, and you don't know how it's going to evolve."

Three years ago the software spawned an inner core, once thought to be idle, that continually spins a little faster than the mantle. Some rank this discovery among the top scientific findings of the decade. Occasionally, the simulated magnetic field practically vanishes and then reappears with the north and south magnetic poles flipped.

"Every once in a while the magnetic field undergoes a reversal of magnetic dipole polarity, and you can't really predict it," Glatzmaier says. "It's exciting when this happens because one simulation, which spans hundreds of thousands of years, takes several months of computer time. During most of this time the field is happy to remain in one polarity state." The mysterious reversals occur on average a few hundred thousand years apart, just like in the actual world.

Had compasses existed at the last reversal 780,000 years ago, they would have pointed to the geographic south instead of the north. The reversal itself would drive compasses crazy, because the poles wander the Earth until they find their new homes. The search typically takes 5,000 years. Since the magnetic field protects the planet from cosmic radiation, some observers speculate that during a reversal the resulting weak and contorted magnetic field may let in enough radiation to change DNA and possibly alter the evolution of some species.

Gary Glatzmaier's supercomputer simulations follow the complexities of the core and the magnetic field it generates. The magnetic field, fluid flow, temperature and densities affect each other.

Glatzmaier and Roberts' simulations are helping answer longstanding questions about how the magnetic field is generated and why it evolves the way it does. In their most recent work, it seems the mantle just above the core may be influencing the reversal frequency.

As described in the journal Nature, they produced eight simulations, each with a different pattern of heat loss from the core to the mantle. "These might represent different times in Earth's history," Glatzmaier said. In some cases reversals occurred more frequently than seen in recent history. In others they happened much less frequently, and one case produced no reversals at all. A pattern modeled on today's lower mantle sprang two reversals over the 300,000 years simulated.

"We find that reversals occur less frequently when we force heat to come out of the core in a pattern matching the natural fluid motions of the outer core," Glatzmaier says. "It's not surprising that this is what it takes to keep things stable, but it is nice to confirm it."