GEOLOGY IS A FIELD OF SCIENCE and aims to solve scientific questions. Every region has a wealth of interesting questions with answers of importance to society. To answer the questions, geologists use their senses and scientific instruments to observe Earth and its processes. They use the resulting observations to answer questions and then, through a series of logical steps, build from observations to explanations.

What Are Observations?

We learn about our world by making observations. We look, listen, smell, and feel so we can record and analyze what is around us. Scientific instruments provide additional information about aspects of the world that we cannot sense, and they allow us to discriminate fine details. For example, we might sense that the temperature outside is near freezing, but if we use a thermometer we can measure a precise value. Every day we make judgments about whether our observations are worth remembering and reliable enough to plan a course of action.

• Geologists, like other scientists, take special care to make valid observations, such as when examining these layers of volcanic ash. An observation that is judged to be valid becomes a piece of data that can be used to develop possible explanations.

• Compasses and other scientific instruments provide quantitative information, provided they are checked and calibrated to ensure that measurements represent valid and trustworthy data. Geologists record data in a field notebook, tablet, or portable computer and collect samples to permit later reexamination and analysis.

• Evaluating the validity of observations is critical, so geologists commonly repeat measurements to compare values. They may bring other geologists out to the field to check and discuss their observations, measurements, and ideas.

How Are Interpretations Different from Data?

Data, by themselves, are not very useful until we analyze them in the context of existing ideas. Perhaps the data will confirm old ideas, or perhaps they will point out a need for a new interpretation. The recent history of volcanic eruptions near Yellowstone National Park illustrates the difference between data and interpretations.

What Is an Explanation?

When geologists examine a collection of related data, several interpretations may fit together to make a coherent story or explanation. The table below summarizes data-interpretation pairs from part B. The bottom row in the table is a new piece of data obtained from other studies. These data and interpretations combine to form a possible explanation, or hypothesis, for how the belt of smooth topography formed.

What Is Happening at Yellowstone National Park?

Geologists have long recognized that several huge volcanic eruptions occurred in Yellowstone during the past two million years. Geologist Bob Smith studied Yellowstone for decades and in 1973 noticed that lake levels along the southern side of Yellowstone Lake had risen, drowning trees. How did he investigate his observations?

To check his observation, Smith and colleagues conducted a new, detailed survey of the area’s topography using high-precision surveying equipment.

This view shows Yellowstone Lake, with north to the left. When Smith compared the new survey
with the last survey done in 1920, he discovered that the elevation of the area shaded orange had increased (the area had risen) in a remarkably short period of time. What was causing this area along the north side of the lake to rise in elevation?

Smith concluded that the rising area north of the lake caused the lake to spill over its southern shoreline, drowning trees in the areas shown in purple.