Journey to the center of the earth.

I am hanging on to the edge of my couch, watching the classic 1950s sci-fi flick Journey to the Center of the Earth. Professor Otto Lidenbrock and his partners venture into Earth's innards to search for a lost underground city. They descend through a volcano and dark tunnels lined with ruby-red crystals. Whipping winds, intense heat, and flash floods threaten them, but the adventurers march on. Suddenly, enormous, scaly, flesh-eating dinosaurs block their path--and boy do those beasts look hungry!

Not willing to watch the explorers get eaten alive, I switch to the evening news. And guess what's making headlines? Read scientists are "journeying" to the center of Earth--making new discoveries all the time. These geophysicists (scientists who study Earth's structure and changes) drill into the surface and use high-tech machinery to "see," "hear," and "feel" what really happens beneath our feet. The best part: They've invited us to come along on their geo-journey. What a trip!

LIFE IN A ROCK

Excuse the tight squeeze: We're gripping the tip of a giant drill, plunging through 30 meters (98 feet) of surface soil into Earth's crust. That's the solid rock that makes up our continents and the seafloor (see miniposter, p. 16). Our first stop: 2.8 kilometers (1.7 miles) beneath the surface. Here, in this rocky part of the planet, scientists recently discovered new forms of life! Forget drooling dinosaurs, though. The critters these scientists dug up are microscopic bacteria that have never before seen the light of day.

"These organisms have enormous survival potential," says T. C. Onstott, a geologist (earth scientist) at Princeton University, who helped drill for the critters. Consider the challenges these microbes face: No light. No water. No oxygen. No room to move around. No real food! Temperatures soar to 85[degrees]C (185[degrees]F). Earth's upper crust pushes down. Yet thousands of newly discovered bacteria call these hot rocks home.

Scientists on the surface are trying to figure out how the bacteria survive. Two things the scientists do know: The microbes "eat" hydrogen for energy and use the carbon in carbon dioxide gas to build their bodies, Onstott says.

The scientists also want to see if these hardy critters could be useful to people. For example, perhaps these bacteria make chemicals that can fight off diseases like cancer and AIDS. As the drill draws up a sample of bacteria for study, we continue our descent.

The deeper we go, the greater the downward pressure from the rocks above. And the hotter it gets, says geophysicist Elise Knittle of the University of California (see sidebar, p. 19). By the time we reach 100 kilometers (60 miles) down, the temperature has surged to 1,000[degrees]C (1,800[degrees]F), hot enough to melt rock!

HOT STUFF

No longer on solid ground, we've hit the bottom of Earth's tectonic plates, the giant slabs of crust and partially melted rock that cover the globe like interlocking puzzle pieces. The plates float on the fiery-hot mantle, the thickest layer of Earth, which churns around us like gooey taffy.

As we plunge into this partly melted layer, we feel the tectonic plates above us start to shift. Scientists say these plates constantly shove against each other, spread apart, or grind past one another. "The plates move a few millimeters or a few centimeters a year," says Knittle. When they shift suddenly, the result can be a deadly earthquake, like the one that flattened an island town off the east coast of Russia last May.

Of course, no one's ever really traveled 2,900 kilometers (1,800 miles) into the mantle to witness these events in person. So how do scientists know what's going on?

USE YOUR SENSES

To "take us" into the mantle--and below--scientists trace the paths of seismic waves. These waves are bursts of sound energy, waves of energy produced by vibrations. On the surface, scientists use high-tech tools to "listen" as seismic waves travel through Earth from a variety of sources, for example, from earthquakes and huge human-made explosions.

What makes the seismic waves useful to a geophysicist is that the waves zip through Earth at different speeds, depending on what they're traveling through. For example, the sound waves travel fast through solids, like the crust on Earth's surface. That's because solids have more molecules packed tightly together to transfer the sound waves from one molecule to the next.

But some waves slow down or fade out when traveling through liquids, like the semi-liquid mantle, explains Ronald Cohen, a geophysicist at the Carnegie Institution of Washington. By listening to the seismic-wave patterns, scientists can determine which layers of Earth are solid or liquid, and even what minerals or metals those layers are made of.

Without these kinds of seismic data, we'd never complete our "journey" to the very center of Earth--its core. According to seismic finds, Earth's core looks nothing like the vast, blue underground sea discovered by Professor Lidenbrock in his movie journey. Instead, it has an outer layer of liquid iron and other churning metals "whipping around the [inner] core," Knittle says.

Despite temperatures rivaling those on the surface of the Sun (higher than 5,000[degrees]C, or 9,032[degrees]F), the inner core is solid iron. Why doesn't the metal stay melted in that intense heat?

It can't stand the pressure, says Knittle. The intense pressure of all the layers above compress the iron core into a solid ball.

Geophysicist Ronald Cohen and his colleagues recently found that Earth's solid center is like a single, moon-size iron crystal. They were trying to explain why earthquake waves take longer to travel through Earth from east to west than from north to south. After using a computer to explore the different properties of iron, Cohen's team concluded that the structure of an iron crystal at Earth's core could explain the difference in speed.

That is, the atoms in an iron crystal are more densely packed in one direction than another, causing the sound waves to travel through at different speeds. Now other scientists are scrambling to find seismic data that either support or reject Cohen's hypothesis.

BACK TO THE SURFACE

So you see, scientists' real-life journey to the center of Earth is far from over. Sci-fi explorer Otto Lidenbrock would certainly encourage scientists to keep digging up answers to Earth's mysteries. At the end of the movie, Lidenbrock declares: "The [human] spirit cannot be stopped. Maybe someday one of you will pick up where we left off."

RELATED ARTICLE: EARTH: ALOOK INSIDE Wondering how you can travel inside planet Earth? No worries! Our map takes you there.

LIFE UNDERGROUND

Drilling 2.8 kilometers (1.7 miles) into Earth's outer rocky crust, scientists recently discovered living bacteria. No one expected to find any life in this 85[degrees]C (185[degrees]F), airless environment.

HOT-ROCK CYCLE

Where slabs of Earth's crust (tectonic plates) collide, chunks of surface rock sometimes break off. These "cool" chunks melt as they plunge into the mantle, a layer of hot, partially melted rock below. When the rock heats up, it may rise again to Earth's surface and burst through a volcano as lava.

CURRENT EVENTS

Currents of sinking cool rock and rising hot rock--convection currents--occur throughout the mantle (arrows). Some scientists say these currents cause the tectonic plates above to shift.

DOWN TO THE CORE

Earth's "steamy" center has two layers: a melted metal outer core and a solid-iron inner core. The center, though hot, is solid because extreme pressure from the layers above compresses it into a solid ball.

QUAKE BREAKS

When two tectonic plates grind past each other, rocks on either side sometimes "catch." Pressure builds until suddenly the plates shift. CRACK! An earthquake occurs. Quakes send out seismic waves, bursts of sound energy. Scientists on the surface can learn what Earth's innards are made of by "listening" to how fast these waves travel through the planet.

EARTH'S CENTER

The total distance from Earth's surface to the center of its core is 6,440 kilometers.

RELATED ARTICLE: TOTALLY COOL CAREER

Geophysicist Elise Knittle digs into Earth's mysteries

When I was a teen, I wanted to be a doctor. But when I got to college, I realized that discovering new things in science could be fun.

In college, I studied physics and astronomy. I found out that some of the most exciting discoveries in our solar system are occurring right here on Earth. So I went to graduate school to study geophysics, the study of Earth's structure and inner workings. Now I research what happens to minerals under the crushing pressures inside Earth.

To find out more about careers in earth science, write:

Earth Science Info. Center U.S. Geological Survey 507 National Center Reston, VA 22092