field and observe events that have already happened, such as the formation of rocks, rock layers, or features of the landscape. Scientists make these observations without changing any aspect of the event or its result.
Geologists also use another kind of experiment called a manipulative experiment. A manipulative experiment is done in a laboratory, where the scientist can manipulate or change certain factors in order to test which factors are most important in creating the observed outcome. In this case, multiple experiments can be done, each one testing the importance of a different factor (or variable), with the goal of zeroing in on the one (or ones) that explain the observed outcome.
Crunching the numbers
After running experiments and making observations, a scientist is left with a large collection of information, or data, to use to draw a conclusion. Trying to find patterns in page after page of descriptive observations or lists of numbers is almost impossible. To find patterns in the data, a scientist uses statistics.
Some people find statistics intimidating because they seem like complicated mathematical formulas. But really, statistical methods are simple mathematics combined in a step-by-step sequence to uncover patterns in the data. Some statistics determine if two sets of data have overall similarities or differences. Others determine which variables are most important in creating the observed outcomes.
Another reason scientists organize and describe their data quantitatively is so that they can display it using graphs. Many different types of graphs are used, and a scientist must determine which type of graph best displays the data in an understandable way. The most suitable graph depends on what type of data is being displayed. Figure 2-1 illustrates a few common graph types used in earth science:
Pie graph: This type of graph is best used for illustrating different pieces of a whole. The total of a pie chart must always add up to 100 percent.
Bar graph: Also called histograms, bar charts are used to display information that can be sorted into different categories.
Scatterplot: Scatterplot graphs illustrate how two types of data are related. Sometimes a scientist will use a scatterplot to look for patterns of relationship between the data types — by finding clusters of data points.
Line graph: This type of graph is most commonly used to plot changes in a type of data over time, distance, or other variable.
FIGURE 2-1: a) Pie graph; b) Bar graph; c) Line graph; d) Scatterplot.
Interpreting results
After data has been described, compared, and graphed, the next step is interpreting the data to draw new conclusions and perhaps propose a new hypothesis for further testing. Often scientists will find that the patterns in their data bring up new questions for exploration.
The challenge at this stage is applying previous knowledge (perhaps from previous experiments) to understand what the patterns in the data — or the relationships between variables — mean. Rather than finding answers to all the questions, scientists often find themselves asking new questions and circling back to the hypothesis stage, preparing to test another hypothesis.
Sharing the findings
When a scientist has completed experiments, analyzed data, and interpreted the results, he must share his findings and ideas with other scientists. Commonly this step is done through scientific journals that are peer-reviewed, meaning that other qualified and respected scientists have examined the experimental design and procedure, perhaps tested it themselves, and determined that the results and interpretation are reasonable.
The peer-review step is very important. The process of having other knowledgeable scientists — other specialists in a particular topic — double-check the work helps find any errors. Errors may lead to false results or incorrect interpretations. Having more than one eye look for errors reduces the potential for moving forward on such false assumptions.
Building New Knowledge: A Scientific Theory
The goal of scientific study is to better understand the world. Step by step, information is collected until a broader or deeper understanding is gained. Eventually, this understanding may be expressed as a scientific theory. As scientists create and share theories, they expand what we know about the world around us.
It’s never “just a theory”
Most people use the word theory to refer to an educated guess — a hypothesis. But scientifically speaking, a theory explains how some complex process works in the natural world. For example, the theory of plate tectonics that I cover in detail in Chapter 10 explains how crustal plates on the earth move around, forming mountains and volcanoes and causing earthquakes. The theory explains how all those geologic processes and resulting features are related to one another through the movement of crustal plates.
When a scientist describes something as a theory, she has come to the end of a long series of experiments and hypothesis testing. She is able to explain something so well, to provide evidence for that explanation (and to have that something accepted by other scientists as true) that it can be called a theory.
