National Oceanic and Atmospheric Administration (NOAA) 89

Science | SERVICE | Stewardship UNDERSTAND THE EARTH

Wooly Magma

Descend into the crater of Yocul of Sneffels, which the 

shade of Scartaris caresses, before the kalends of July, 

audacious traveler, and you will reach the center of the 

earth. I did it.

“All scientific teaching, theoretical and practical, 

shows it to be impossible,” I said.

“I care nothing for theories,” retorted my uncle.

“But is it not well-known that heat increases one 

degree for every seventy feet you descend into the earth? 

Which gives a fine idea of the central heat. All the matters 

which compose the globe are in a state of incandescence; 

even gold, platinum, and the hardest rocks are in a state 

of fusion. What would become of us?”

“Don’t be alarmed at the heat, my boy.”

“How so?”

“Neither you nor anybody else know anything 

about the real state of the earth’s interior. All modern 

experiments tend to explode the older theories.”

~ from A Journey to the Center Of the Earth, by Jules Verne

jv.gilead.org.il/vt/c_earth/

Most of what Jules Verne wrote about the 

center of the Earth in 1864 is now considered 

to be wrong. While it is still true that no one 

has actually seen the Earth’s interior, today’s 

“scientifi c teaching, theoretical and practical” 

agrees more with young Harry than with his 

adventurous uncle. The center of the Earth is 

now believed to have an average temperature 

of 7,000°F, with maximum temperatures as 

high as 13,000°F. Here’s a way to show what 

scientists think we might fi nd if we could really 

take a journey to the center of the Earth.

What You Will Do

Make a colorful model of Earth’s structure

Most of what Jules Verne wrote about the 

center of the Earth in 1864 is now considered 

to be wrong. While it is still true that no one 

has actually seen the Earth’s interior, today’s 

agrees more with young Harry than with his 

adventurous uncle. The center of the Earth is 

now believed to have an average temperature 

of 7,000°F, with maximum temperatures as 

high as 13,000°F. Here’s a way to show what 

scientists think we might fi nd if we could really 

take a journey to the center of the Earth.

Wooly Magma

Overfl ow from Mauna Ulu Crater. View east at overfl ow from 

trench into main Mauna Ulu crater on March 19, 1972. Note 

partially cooled skin on lake. Photo credit: R.T. Holcomb, Hawaiian 

Volcano Observatory, U.S. Geological Survey.
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What You Will Need

r Two containers that will each hold about eight 

quarts (pots or bowls are fine)

r Paper towels 

r Hand towel 

r Dishwashing liquid

r Sharp scissors 

r Serrated knife and a cutting board 

r Rubber ball, about 1-1/4 inches diameter

r Wool roving in six colors; about 2/3 ounce of 

each color (red, gold, pink, green, white, and 

blue are suggested, but any colors will work)

r Hot and cold tap water

r Ice (about seven pounds)

Warnings

1. Be careful with scissors and hot water!

2. Get help from an adult to use the serrated 

knife!

How to Do It

To make your model, you will use a process called 

“felting.” You can read more about felting and 

how it works under “What’s Happening” at the 

end of this section.

1. Here is a drawing that shows the layers of 

Earth’s structure that will be included in your 

model. Since no one has actually seen Earth’s 

interior, we don’t know what the true colors 

are. So for your model, choose some colors 

that you like, and that are different enough 

so that the layers can be easily seen.

2. Begin constructing your model with the rubber ball, which represents the INNER CORE. 

Wrap a piece of red wool roving around the 

ball. The red roving represents the OUTER CORE. Be sure to wrap the wool roving 

tightly, and try to switch directions as often 

as possible. Pull the fiber as thin as you can. 

When you’ve reached the end, pull the fibers 

out to be as light and transparent as cotton 

candy; smooth those ends over the ball by 

stretching and patting them into place so 

they neatly stick to the ball. This will make 

the felting process easier because the fibers 

can be interlocked better that way.

3. Fill one of the containers about 2/3 full with 

hot tap water (the water should be as hot 

as your hands can stand). Fill the other 

container about 1/2 full with ice, then 

add cold tap water until the container is 

about 2/3 full.

4. Now for the felting! Dunk your woolen ball into either the hot or ice cold 

water. Hold the ball under the water 

and squeeze it hard to make sure water 

penetrates all the way to the inner core 

ball. Lift the woolen ball out of the water 

and squeeze again. Put a couple of drops 

of dishwashing liquid on the woolen ball, 

and roll the ball in your hands lightly, quickly and evenly. After the fibers 

have joined, begin to slightly increase 

pressure. The harder and faster you roll, the 

faster the felting process takes place.

5. After about a minute, dunk the ball into the 

other water container (so if you dunked it in 

cold water first, dunk it in hot water now.) 

The change of temperature shocks the wool 

fibers and makes them cling together.

6. Repeat the rolling process, adding more 

dishwashing liquid only if you need to. Too 

much soap will make the ball slippery and 

hard to press against. If the ball gets too 

soapy, rinse or blot off the excess dishwashing liquid with a paper towel. After about 5 

Inner Core

Outer Core

Mantle

Transition Zone

Asthenosphere

Lithosphere

Structure of the Earth

Crust
National Oceanic and Atmospheric Administration (NOAA) 91

Science | SERVICE | Stewardship Understand the Eart

minutes, you should have a hard, tight ball. 

Now you are ready to add the next layer. 

7. Wrap the gold-colored roving around the ball 

to represent the lower Mantle layer. Remember to wrap the wool tightly, roll it in different directions, pull the end fibers out to be 

very thin, and smooth those ends over the 

ball.

8. Repeat Steps 4, 5, and 6. 

Are you feeling tired? Felting is hard work – if 

you’re not feeling your muscles, you’re not 

working hard enough! 

9. Wrap pink roving around the ball to represent 

the Transition Zone, remembering to wrap 

the wool tightly, roll it in different directions, pull the end fibers out to be very thin, 

and smooth the ends over the ball.

10. Repeat Steps 4, 5, and 6. 

11. Next, add a layer of green roving to represent 

the Asthenosphere. You guessed it —Repeat 

Steps 4, 5, and 6. 

12. Only two layers to go! Wrap the white roving 

around your ball to represent the Lithosphere, and repeat Steps 4, 5, and 6. 

13. At last! It’s time to add the final layer to 

represent the Crust. This could be blue, 

since most of Earth’s surface is covered with 

water, or multi-colored to represents both 

continental and oceanic crusts. Wrap the last 

piece of roving and repeat Steps 4, 5, and 6.

14. When you have finished your model, the 

felted wool ball should feel as firm as a 

tennis ball. Now, ask your adult partner to 

cut around the globe with a serrated knife 

to open the model up. WARNING—Be sure 

to ask your partner not to cut all the way 

through! Leave a hinge area about 1/2 inch 

wide, or the whole thing will fall apart! 

Carefully pull your model open and remove 

the ball. Trim any loose ends with scissors 

to make it uniform and smooth. Put the ball 

back in and ADMIRE your Wooly Magma—it’s 

yours and it’s unique! No two are alike.

What’s Happening

More about Felting

What is felt? Do you know what it is made of? 

Have you ever seen someone throw a pair of 

woolen socks or a wool sweater in the washing 

machine and then the dryer? What happens to it? 

It shrinks! Almost anything made of 100% natural fiber can be felted. During felting, the tiny 

fibers that make up the wool interlock; tightening and closing the small holes that are also part 

of its make up. The felting process is basically a 

compacting of the material that makes the fibers 

very dense. 

Three things are needed to felt wet/moist wool: 

ALKALINITY, HEAT, and AGITATION. In short AHA! 

Any two of them together will lead to a natural 

fiber or fabric felting. If you have a dog, cat, 

rabbit, or other pet with long fine hair, you’ve 

probably noticed mats or clumps behind its ears 

or on the body wherever the hair is exposed to 

AGITATION and moisture. That’s felt! If you’ve 

shampooed those spots on your animal, you’ll 

notice how hard and dense those clumps of fur 

become. That’s because you’ve added the ALKALINITY and intensified the felting process. 

To make your model, you use your muscles and 

a lot of “elbow grease” for the AGITATION. The 

HEAT part comes in when you shock your wool 

by dunking it into ice cold water and then in hot 

water. Dishwashing liquid provides the needed 

ALKALINITY for the process. 

Why would people want to make felt on purpose? 

It can be beautiful and decorative, but more important, it is much warmer than a loosely woven 

garment. It can become nearly impenetrable; 

almost waterproof, and was especially important 

for the people who lived in the day when there 

were no synthetic fibers like nylon, polyester, or 

acrylic that our winter garments are made of now. 

More About Earth’s Layers

Earth’s CORE is made out of iron and nickel and is 

about 1,550 miles in diameter. The temperature 

of the INNER CORE is on average about 7,000 degrees Fahrenheit, but it can go up to 13,000 degrees Fahrenheit. To give you an idea of how hot 

that is, you can bake a loaf of bread in your oven 

at 350 degrees and rock begins to melt at 1,600 
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degrees. Under the immense pressures in 

the INNER CORE, the metals do not fl ow as 

a liquid despite the high temperatures, but 

behave and vibrate like a solid.

The OUTER CORE is a sphere of iron and 

nickel, under less pressure than the inner 

core and nearly as hot. Here the metals 

are in a liquid state; between 4,000 and 

9,000 degrees Fahrenheit. The Outer Core 

is 1,400 miles thick, located about 1,800 

miles beneath the crust. Scientists believe 

that the circulation of an electric current 

in the Outer Core causes the Earth’s magnetic fi eld. 

The MANTLE is Earth’s largest layer, and is 

approximately two thirds of Earth’s total mass. It 

is divided into several parts. The LOWER MANTLE 

(our gold layer) is very dense and hot (4,000 

degrees Fahrenheit).

The TRANSITION ZONE divides the lower mantle 

from its upper portion. The Transition Zone starts 

at a depth of 250 miles and is roughly 190 miles 

thick. The temperatures here are much cooler 

than the lower mantle, around 1,600 degrees 

Fahrenheit.

The ASTHENOSPHERE is in the upper region of the 

mantle, and is the part that fl ows like asphalt. It 

both moves the plates of the Earth and permits 

their motion. This ability of a solid to fl ow is 

called “plasticity”.

The LITHOSPHERE is a slab about 45 miles thick 

in which the continents are embedded. It gives 

us mountains and trenches (collisions), seafl oor 

spreading and new oceans (separation), and long 

earthquake faults, like the San Andreas Fault 

(sliding side-by-side). This zone is composed of 

rigid, brittle rock.

The EARTH’S CRUST is the thinnest layer of the 

Earth at only 3-5 miles thick under the oceans 

and about 25 miles thick under the continents. It 

is composed of two basic rock types: granite and 

basalt. The CONTINENTAL CRUST is mostly granite 

while the OCEANIC CRUST consists of a volcanic 

lava rock called basalt. Temperatures vary from 

air temperature to 1,600 degrees Fahrenheit. It is 

here that volcanoes are started and where we fi nd 

rich soil, jewels, and rocks. We live on the 

Earth’s Crust.

Please note that the layers we use in this 

project are not in scale to the Earth’s 

real layers. They are too similar in size. 

Also, the colors have nothing to do with 

how the Earth looks underneath. No one 

really knows what the layers look like. 

We’ve used color just for fun and to make 

a contrast so we can pick out each layer 

more easily.

Want to Do More?

For more information about Earth and its structure, visit:

pubs.usgs.gov/gip/dynamic/inside.html

www.windows2universe.org/?page=/earth/Interior_Structure/overview.html

www.pbs.org/wnet/savageearth/hellscrust/index.html?pagewanted

This activity was created by Annie Reiser, Global Systems 

Division Visitor Information Specialist at NOAA’s Earth System 

Research Laboratory

Two automobiles are all that remain after this section of Royal Gardens subdivision 

was overrun by lava (October 7, 1987). During October the footpath from a road into 

the housing area was covered, cutting residents off from the few homes that remained. 

Photo credit: J.D. Griggs, Hawaiian Volcano Observatory, U.S. Geological Survey