planet’s rotation. If the surface layers are less dense than the average for the planet, then
the interior must be denser than the average. Calculations indicate that the core is about
85% iron metal with nickel metal making up much of the rest. These proportions agree with
those seen in metallic meteorites. Seismic waves indicate that the outer core must be liquid
and the inner core must be solid.
If Earth’s core were not metallic, the planet would not have a magnetic field. Metal conducts
electricity, but rock—which makes up the mantle and crust—does not. The best conductors
are metals that can move, so scientists assume that the magnetic field is due to convection
in the liquid outer core. These convection currents form in the outer core because the base
of the outer core is heated by the even hotter inner core.
Lesson Summary
- The Earth is made of three layers: the crust, mantle and core.
- The brittle crust and uppermost mantle are together called the lithosphere.
- Beneath the lithosphere, the mantle is solid rock that can flow, or behave plastically.
- The hot core warms the base of the mantle, which cause mantle convection.
- Mantle convection is very important to the theory of plate tectonics.
Review Questions
- List two ways that scientists learn about what makes up the planet’s interior.
- What types of rock make up the oceanic crust?
- What types of rock make up the continental crust?
- List two reasons that scientists know that the outer core is liquid.
- Describe the properties of each of these parts of the Earth’s interior: lithosphere,
mantle, and core. What are they made of? How hot are they? What are a few of their
physical properties? - Suppose that Earth’s interior contains a large amount of lead. Based on your prior
knowledge, how dense is lead? Would the lead be more likely to be found in the crust,
mantle, or core? - When you put your hand near a pan above a pan filled with boiling water, does your
hand warm up because of convection or conduction? If you touch the pan, does your
hand warm up because of convection or conduction? Based on your answers, which
type of heat transfer moves heat more easily and efficiently?
Vocabulary
conduction The process in which energy moves through matter as heat by direct contact,
moving from an area of higher temperature to an area of lower temperature.