Lesson Goals Compare the
Identity
ad hoc
Explain how Comics
God Kepler
couple of
Words to know
Fill in this table as you work through the fosson. You may use the glossary to
help you
a model of the solar system where planets orbit the Sun
a small chunk of rock and metal debris in space
belonging to or related to the sky
a mini-orbit that explains the variations in movement of
planets in the solar system
a small object made of ice and dust that orbits the Sun
a rocky object that orbits the Sun
a model of the solar system where the Sun and plants
orbit around Earth

the earth’s crust is broken into separate pieces called tectonic plates (fig. 7.14). recall that the crust is the solid, rocky, outer shell of the planet. it is composed of two distinctly different types of material: the less-dense continental crust and the more-dense oceanic crust. both types of crust rest atop solid, upper mantle material. the upper mantle, in turn, floats on a denser layer of lower mantle that is much like thick molten tar.

each tectonic plate is free-floating and can move independently. earthquakes and volcanoes are the direct result of the movement of tectonic plates at fault lines. the term fault is used to describe the boundary between tectonic plates. most of the earthquakes and volcanoes around the pacific ocean basin—a pattern known as the “ring of fire”—are due to the movement of tectonic plates in this region. other observable results of short-term plate movement include the gradual widening of the great rift lakes in eastern africa and the rising of the himalayan mountain range. the motion of plates can be described in four general patterns:

collision: when two continental plates are shoved together

subduction: when one plate plunges beneath another (fig. 7.15)

spreading: when two plates are pushed apart (fig. 7.15)

transform faulting: when two plates slide past each other (fig. 7.15)

which of the following is a subsurface event that takes place during the rock cycle?