SCIENCE

How far would you have to travel to reach the Earth’s core? And what would you see along the way? Use this interactive to dig into the truth. (BBC)

Download our own high-resolution illustration of Earth’s interior.

Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit.

Discussion Ideas

• Scrolling through the fantastic BBC interactive graphic of Earth’s interior, it seems like the crust takes up a lot more room than the mantle or core. Just the opposite is true in our own illustration of Earth’s interior, which shows the upper and lower mantle—not the crust—as the thickest layer in Earth’s interior. Why is there such a difference?
  • Scale! Scale is one of the most important concepts in mapping. Scale is the relationship between distances shown on a map and actual distances in the real world. (Learn more about scale with this activity.) Large-scale mapping allows much greater detail than small-scale mapping. (Just remember: large-scale map=small details.)
    • Take a look at the bottom of the “Journey to the Center of the Earth” interactive graphic. It shows distance and scale. As you scroll down, you can see the scale going from large-scale to small-scale.
      • Near the surface of the Earth, one pixel represents about .002 meter (2 millimeters). That leaves a lot of room for information about drilling, diving, and metal detectors.
      • At the deepest place yet reached by people (hi, James Cameron!), one pixel represents one meter.
      • Toward the center of the Earth, one pixel represents 2,500 meters (2.5 kilometers). At this scale, you can move through the entire core in one swipe!

• The BBC graphic drills deep into the earth and dives deep into the ocean to show “what lies beneath” the surface. At about 10 meters (33 feet), the graphic starts to note how divers may experience “nitrogen narcosis,” a phenomenon similar to alcohol intoxication. People living and working at the same depth in solid ground don’t experience this phenomenon. Why?
  • Nitrogen narcosis is the result of breathing gases under high pressure. Here’s a great explanation: “Above sea level, nitrogen is a pretty boring gas—it makes up about 80% of the air around us and doesn’t normally do us any harm. However, a problem arises when we breathe it in under high pressure—such as when diving. Several gases, including nitrogen, carbon dioxide, and oxygen are normally dissolved in our bloodstream. When you dive deep underwater, the increase in pressure exerted on your body by the surrounding water causes more of these gases to dissolve into your blood through your lungs when you breathe from the gas tank (because going deep-sea diving without a gas tank would be an even less recommendable thing to do). . . All that extra nitrogen rushing round in the bloodstream has . . . effects on the brain, collectively known as nitrogen narcosis.”
    • Although nitrogen and oxygen have narcotic effects at high pressure, helium doesn’t. Divers often incorporate helium into their tanks of breathing gas in mixtures known as trimix (which mixes oxygen, helium, and nitrogen) and heliox (which mixes oxygen and helium).

• Both our graphic and the BBC’s “Journey to the Center of the Earth” note the Mohorovicic discontinuity and the Gutenberg discontinuity. (Learn more about the Moho here.) What’s being discontinued? What is the “Moho”? What’s the Gutenberg discontinuity—and why is it called the CMB?
  • The Mohorovicic discontinuity is the boundary between Earth’s crust and mantle. The Moho is not a uniform line—it’s about 5 to 10 kilometers (3–6 miles) below the ocean floor, and 20 to 90 kilometers (10–60 miles) beneath continents.
  • The Gutenberg discontinuity is the boundary between Earth’s mantle and core. CMB simply stands for “core mantle boundary.”

TEACHERS’ TOOLKIT

BBC: Journey to the Center of the Earth

Nat Geo: Earth’s Interior downloadable poster

Nat Geo: Many Ways to Name a Place activity (the role of scale in mapping)

Nat Geo: What is Earth’s core?

Nat Geo: What is Earth’s mantle?

Nat Geo: What is Earth’s crust?