Figure 12.11: The Earth formed at the same time as the other planets in our solar system
about 4 1/2 billion years ago. ( 17 )
center is called its core. The core is made of very dense metal elements called iron and nickel.
The outermost layer of the Earth is its crust. The crust is made mostly of light elements
such as silicon, oxygen, and aluminum. More information on the different layers of the Earth
is presented in the lesson on plate tectonics.
Figure 12.12: The Earth is made of several layers that vary in density. The center of the
Earth is the core, which is the densest. The outermost layer is the crust, which is the least
dense. The middle layers make up the mantle. ( 19 )