How Does Energy Affect the Inside of the Earth?

Explain how conduction, convection and radiation influence the movement of different layers of the Earth, resulting in volcanoes, earthquakes, mountain building, and other results of plate tectonics.


Inside the Earth

A jawbreaker

Have you ever eaten a jawbreaker?  As you eat it, different colors and layers appear until you get to the white center that the jawbreaker company didn’t bother to color.  Maybe they figure that, by the time you get to the middle, you don’t care about the colors any more.  Anyway, it’s easy to see the different layers in a jawbreaker, but it’s not as easy to see them in Earth.

That’s because the Earth is big.  Real big.  If you tried to dig a hole through the center of the Earth to the other side, it would be a 8,000 mile long hole.  Think about it: if you tried to drive that distance at 80 miles per hour, without stopping, it would still take you over four days.  Along the way, you’d get a little chilly, then extremely hot, then boiled and crushed.  And that’s just the first day!

The Earth is made up of four major layers: the crust, the mantle, the outer core and the inner core.  The crust averages about 25 miles in thickness, or about 20 minutes of your 80 mph journey to the center of the Earth.  Not long at all.  But the crust is the furthest down that humans have ever been in the Earth, and it’s where everything else is: water, land, plants, animals, our stuff, etc.  In other words, we know a tremendous amount about the crust but not nearly as much about the other layers.

Layers of Earth

That’s too bad, because the other layers are pretty interesting, too.  The mantle is about 1800 miles thick (almost as long as the Mississippi River) and makes up most of the mass of the Earth.  But it’s hot.  The mantle is 1000F near the core and 4000F near the crust, so watch out!  Despite the fact that it’s that hot, it’s mostly made up of solid rocks, not liquids.  Those solid rocks move around quite a bit, the warmer materials moving toward the crust and the cooler materials moving towards the core.  This is called a convection current, just like the hot air in your house moves towards the attic and the cool air moves towards the basement.

Volcano diagram

Convection currents work because the outer core is super hot.  We’re talking about 6000F.  In fact, it’s so hot that almost any rock found in the outer core is completely melted.  Because the outer core touches the mantle, it uses conduction (heat transfer by contact) to heat up that cool, 1000F rock, and sends it rising up to the top of the mantle.  This keeps the mantle in motion and makes the tectonic plates riding on top of the mantle move.  The bad news?  We live on those plates, and so do the oceans.  The good news?  They only move at about an inch a year, or the same rate as your fingernails.

Types of earthquakes

OK, so really there’s actually some more bad news.  Because the mantle can’t just stay where it is, tectonic plates end up crashing into each other, causing earthquakes, volcanoes and mountain building.  Earthquakes happen when plates crash into each other (normal or thrust) or when they slide past each other (strike-slip).  Volcanoes happen when the mantle finds an opening in the crust and pushes its way through, sending hot magma through the crust as lava.  And mountain building happens when plates push together, but they’re so evenly matched that the only place to go for the plates is up, resulting in nice, pretty mountains.  In fact, the pointier and taller the mountain, the younger it is: the Rockies in the west are much younger than the Appalachians in the east of the U.S.

Finally, you may be wondering how all of this heat came about in the first place – how is it that the core and mantle are so hot?  Well, remember that the Earth bubbled off the sun, so some of that same heat still remains deep inside the Earth.  The inner core is thought to be as warm as the surface of the sun, and is made up of solid metals (mostly nickel and iron). It’s part of the reason that, even when it’s cold outside, it’s still a lot warmer than it is in space.  It’s about -450F in space, so a 15F night doesn’t seem so cold anymore, does it?  Moreover, there’s something else going on that keeps things warm on the surface of Earth.  It’s called radiation.  During the day, electromagnetic radiation, otherwise known as light, strikes the surface of the Earth, warming it up.  At night, some of that heat is released into the atmosphere.  Cloudy days tend to lead to cooler nights due to this phenomenon!

Questions
Remember
1. Name the four layers of the Earth and describe briefly what is inside each one.
2. What makes the tectonic plates move?
3. What would you tell someone who asked you, "Is it true that you can travel to the center of the Earth?" Explain!
Put it together
4. Make a three-way Venn diagram to show the similarities and differences between conduction, convection, and radiation.
5. Geothermal energy is a type of energy that uses the heat inside the Earth to heat up water for use inside peoples' homes. Using the information in this chapter, do you think this type of energy you is a good idea? Why or why not?
Think about it
6. Los Angeles, in California, is on a different tectonic plate than Seattle, in Washington. Los Angeles is currently 1500 km from Seattle, and it's tectonic plate is moving north at a rate of 1 cm per year. How long will it take for Los Angeles and Seattle to be neighbors? Should people in Los Angeles be concerned about this? Sketch out what California might look like in 1 million years.
Review
7. Name three crops that you eat in some form.
8. In what ways is Earth like a living thing?
9. You have already learned that oxygen was not available on the early Earth. Given that information and the information from this chapter, which of these four energy cycles do you think came before the other ones? Which one was next? Which one was last? Give a reason you came up with this order!
10. For each of proteins, carbohydrates and lipids, list what foods they can be found in.
Conduction and Convection Lab
  1. Receive your assigned experiment from the table below.  Check the initial temperature, then start the experiment.
  2. While you are waiting for the experiment to complete, finish the 3rd and 4th columns of the table below.
  3. Once all experiments have concluded, fill in the table with all of the data, then plot the data as follows:
    • Use the experiment number as the independent variable
    • What will the dependent variable be? __________ .   Create a scale for the dependent variable that starts at 0 and has a reasonable maximum.
    • Plot points for each “initial temperature.”
    • For each warmer thermometer, make a red bar from the initial temperature point to the final temperature.
    • For each colder thermometer, make a blue bar from the initial temperature point to the final temperature.  The two colors may overlap.
  4. Look at your hypotheses and then look at the data.  For three experiments that you were most surprised by, write down why you think the data was different than expected in terms of conduction, convection and radiation.
Experiment 1 Experiment 2 Experiment 3 Experiment 4 Experiment 5
Thermometer A placement Bottom of stairwell C Floor of room Ground-level window Bottom of ice-water bucket In direct sunlight
Thermometer B placement Top of stairwell C Ceiling of room Classroom window Top of ice-water bucket In shade
Conduction, Convection, or Radiation?
Hypothesis
Thermometers initial temperature
Thermometer A final temperature
Thermometer B final temperature
Experiment 6 Experiment 7 Experiment 8 Experiment 9 Experiment 10
Thermometer A placement 1″ below fluorescent light 1″ below incandescent light Direct contact with ice cube Direct contact with hot plate Direct contact with metal in ice bath
Thermometer B placement 5 feet below fluorescent light 5 feet below incandescent light Direct contact with table holding ice cube Direct contact with table holding hot plate Direct contact with bucket holding ice bath
Conduction, Convection, or Radiation?
Hypothesis
Thermometers initial temperature
Thermometer A final temperature
Thermometer B final temperature
Build Your Own Seismograph
From the Regents of the University of California

You need to understand how a seismograph works. A typical seismograph works in a very simple way:

  • A heavy weight is fastened to a rod of some sort.
  • This rod hangs from a pole and is free to swing from side to side when the ground shakes.
  • At the other end of the rod (away from the pole) is an ink pen, and directly underneath the pen is a piece of paper.
  • If the ground does not move, the rod does not swing, and the pen stays in place.
  • If the ground shakes, however, the rod swings and so the pen draws a zigzag line. The stronger the shaking, the sharper the zigzags. This zigzag picture made on the paper roll is called a seismogram.

  1. You will use the following materials (at least) to make your own seismograph: springs, rubber bands, clay, marbles, washers, paper plates and cups, pencils, pieces of wood, and tape.
  2. Your seismograph should be able to detect motion on any surface on which it is placed by the marking of a pen or pencil on some piece of paper.
  3. Test your seismograph by shaking the table gently at first.  Shake it with various intensities to see the effects of different movements.
  4. How could a device like this be useful to society?
  5. What modifications would have to be made to make this device more useful?
  6. How could you improve your design, given the materials that you have?
  7. Look around at others’ devices.  What are some features of other groups’ devices that you would like to adopt in your own?
  8. Why is it important to consider many different options when deciding upon a particular design for a technological device?  Answer as a short-answer question.