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The JR bobbed in the ocean. The boat's drill dug into the ocean floor. It pounded into the hard rock. Scientists on the ship were excited. Could they drill deep enough? If so, they might discover new facts about Earth's story.

And what a long story it is. Earth is over 4.5 billion years old! At first, it was just a big blob of melted rock.

Slowly, the planet cooled. The heaviest things such as iron sank down. Lighter materials rose up. Over hundreds of millions of years, the materials formed three main layers.

No one has drilled to Earth's deepest layers. Not yet, at least. But scientists know what the layers are like. By studying earthquakes, they know some layers are made of liquid metal. Other layers are made of hard rock.

To picture Earth, think of a boiled egg. Picture the yolk, egg white, and shell. Earth's "yolk" is called the core. It is the deepest layer. The core is very hot!

Next is Earth's thick mantle. It is like the white part of the egg. The mantle is made of partly melted rock.

Finally comes Earth's cool crust. It is like the eggshell—the thinnest layer. The crust is where we live. All you see is part of it. Valleys, fields, and even the oceans are part of the crust.

The crust may look solid. It's not. It is broken into huge pieces, like a jigsaw puzzle. The pieces are called tectonic plates. These plates float on top of the mantle. They are always moving. Here's what scientists think happens.

The hot core heats the mantle. That makes the partly melted rock rise up. When the rock moves away from the core, it cools. Then it sinks again. This push and pull from below makes the plates move.

The plates move very, very slowly. The fastest plate only moves about 15 centimeters (6 inches) per year. Yet those inches add up! Bit by bit, the plates pull continents apart.

Long ago, the continents were joined together. Over millions and millions of years, they moved apart. They continue to move. In the future, Earth will look much different than it does now!

Moving plates crash into each other. That means lots of action! Volcanoes, earthquakes, and even mountains are made by shifting plates.

Most of the action happens where plates meet. At a convergent boundary plates crash into each other. Both plates push up. This can create huge mountains.

Sometimes an ocean plate bumps into a continental, or land, plate. Then the heavier ocean plate drops down. The deeper into Earth it goes, the hotter it gets.

At a divergent boundary, two plates move apart. As they do, deep valleys form. Volcanoes erupt. Magma, or molten rock, oozes into the gap. In parts of Iceland, you can see the gap between plates.

At a transform fault, two plates slide past each other. That's what is happening in California.

Earthquakes shake the state as the Pacific plate creeps north. And Los Angeles is riding on top! In about 29 million years, the city will slide 350 miles north and pass San Francisco.

You can see lots of action along the Ring of Fire. That is along the edges of the Pacific plate. About 80 percent of Earth's earthquakes happen here. About 75 percent of active land volcanoes erupt here.

To see the Ring, look at a map of the Pacific Ocean. Volcanoes are all around it! On the east side, huge volcanoes rise up. Mount St. Helens is an example. You can find others in Washington as well as in California, Oregon, and Alaska.

We know how Earth's hot core shapes our home on the crust. But deep down, Earth still holds many secrets. That's why the scientists on The JR keep drilling down, down, down.

It may take 10 to 20 years before scientists reach the mantle. What an exciting moment that will be! What will mantle rock look like? What will it tell us about Earth?

Scientists may learn what's going on deep in our planet. Stay tuned for the next chapter in Earth's story.

Article by Beth Geiger. Top-of-page image by National Geographic Maps. "Active Earth" appears on page 8 of the Jan.-Feb. 2010 issue.