Journey to the Center of the Earth
Introduction:
If you could ride in a magic car and travel to the center of the Earth, what would you see,
and how long would it take to drive from the surface to the very center of the Earth? What you
would see would depend on how you classify the different layers. Will you classify the layers
based on their composition or their physical properties? The time required for your trip, of
course, would depend on your speed. Let’s assume that two magic cars are going to the center of
the Earth. One, the Core Seeker, will classify the layers based on composition. The second car,
Hard Rocker, will classify the layers based on physical characteristics. Let’s assume that both
cars are traveling at 100 kmph or 60 mph.
The Core Seeker
The Core Seeker begins its trip on the surface of the crust. As you enter the solid
continental crust, you see yourself surrounded by granite. You continue downward for about 20
minutes traveling through 35-40 km of solid granitic crust rich in silica. You may encounter
pegmatite as you dive deeper where the rocks have cooled more slowly.
If you had entered the crust at the bottom of the ocean, you would have been surrounded
by basalt. This dark fine-grained mafic rock is solid, but not very thick. You could travel through
the 7 to 10 km of oceanic crust in only five minutes or so. After passing through the crust, you
reach the mantle. This semi-solid layer is the largest portion of the Earth. It is about 2,900 km
thick and contains about 67% of the Earth’s total bulk. The rocks surrounding you are called
peridotite. Traveling at 100 kmph, it would take 29 hours of continuous driving to cross this
layer.
The Core Seeker has finally reached the core. The outer core begins at about 2900 km
and continues down to 5,155 km. The outer core is about 2,255 km thick. It is molten and made
of an alloy of iron, nickel, and other elements such silicon, oxygen, and sulphur. This liquid layer
of the Earth circulates creating the Earth’s magnetic field. The inner core is also made of an alloy
of iron and nickel. This solid layer has a radius of about 1,220 km. The temperature at this depth
may reach 4,700 degrees C or almost 8,500 degrees F.
The Hard Rocker
If you were to travel in the Hard Rocker, you would first encounter the lithosphere. This
layer of crust and upper mantle is rock solid. The lithosphere averages about 80 km thick over
much of the Earth. It can reach a thickness of 150km under mountain systems. The
asthenosphere begins at the base of the lithoshpere. The asthenosphere begins when the
temperature reaches about 1,280 C. This is the temperature at which rock can flow. Many people
think of the asthenosphere as being liquid, it is not. The asthenosphere can flow slowly. The
fastest rate of flow is about 10 to 15 cm/year. The lower limit of the asthenosphere is harder to
determine, but many geologists place it at about 600km. This is the transition zone which starts
at a depth of about 400km.
The lower portion of the mantle is called the mesosphere. This more rigid portion of the
mantle extends down to the outer core at a depth of about 2,900km. Below the mesosphere,
starting at 2,900 km or 1,740 miles is the outer core. This molten or liquid portion of the earth
reaches temperatures over 4,000 C. Finally, the Hard Rocker reaches the inner core. This solid
layer is about 1,220 km in radius from the center of the Earth. Temperatures of the inner core
may exceed 4,700 C.
Conclusion
Explorers aboard the Core Seeker and Hard Rocker were amazed that the outer core was
molten while the inner core was solid. What could explain this? The temperatures within the core
were hot enough to melt any rock. The answer seems to be related to pressure. The pressure
gauges on both vehicles continued to go up until they reached the center of the Earth. The
pressures on the inner core are so intense that the matter cannot melt. Over time, as the Earth
cools, the size of the inner core will probably increase at the expense of the outer core. This is a
very slow process.
Journey to the Center of the Earth Journal Response Questions:
1. Traveling at 100 kilometers per hour, how long would it take the Core Seeker to reach the
very center of the Earth? (Assume the crust is 50 km thick.)
2. Why is it not possible to actually travel to the center of the Earth?
3. How have scientists learned about the interior of the Earth?
4. Mechanically, how do the following layers compare to each other?
Lithosphere to asthenosphere
Mesosphere to outer core
Outer core to inner core
5. Based on composition, how do these layers compare?
Crust to mantle
Mantle to core
Oceanic crust to continental crust
6. How does the density of the layers change as the depth increases?
7. Which layer is responsible for generating the Earth's magnetic field?