Key Concepts
What is the science of geology?
What are the characteristics of Earth's principal layers?
Vocabulary
geologists
uniformitarianism
crust
silicates
mantle
lithosphere
asthenosphere
mesosphere
core
Reading Strategy
Building Vocabulary Draw a table similar to the one below that includes all the vocabulary terms listed for the section. As you read the section, define each vocabulary term in your own words.
Vocabulary Term |
Definition |
---|---|
Geologist |
a. |
Uniformitarianism |
b. |
Crust |
c. |
In many ways, scientists know more about the structure of the universe and the workings of microscopic cells than they do about the ground beneath their feet. With a telescope, an astronomer can see stars at the farthest edges of the universe. With a microscope, a biologist can see the inner structure of cells. But there is no instrument that allows geologists to look deep inside Earth. The reason is both simple and profound: light does not travel through most rocks.
Though scientists cannot see into Earth, in a sense they can listen to it. The waves from earthquakes travel through Earth in a manner similar to the way that sound waves travel to our ears. These waves vibrate within Earth and are recorded at Earth's surface. Scientists are able to interpret these waves to learn about the structure and composition of Earth's interior. Scientists have also drilled holes to a depth of about 12 kilometers to collect data on the uppermost portion of Earth's interior. Figure 1 shows one such drilling effort.
Figure 1 These workers are drilling a hole that will be more than two kilometers deep. Later they will lower instruments into the hole to record data at that depth.
Geology is the study of planet Earth, including its composition and structure. Scientists who study Earth and the processes that have shaped Earth over time are called geologists. Geologists such as the one shown in Figure 2 divide the forces that change Earth's surface into two groups: constructive forces and destructive forces. Constructive forces shape the surface by building up mountains and other land areas. Destructive forces slowly wear away mountains and, eventually, every other feature on Earth's surface.