# 1.4 We Study Earth Using the Scientific Method

There is no single method of inquiry that is specifically the scientific method.  Furthermore, scientific inquiry is not necessarily different from serious research in other disciplines. The key features of serious inquiry are the following:

• Creation of a hypothesis. This is a tentative idea about how to explain a set of observations.
• Test the hypothesis.  A hypothesis can be used to make predictions, and experiments can be run to see if those predictions are correct.

# An Example of the Scientific Method at Work

Consider a field trip to the stream shown in Figure 1.5. Notice that the rocks in and along the stream are rounded off rather than having sharp edges. We might hypothesize that the rocks were rounded because as the stream carried them, they crashed into each other and pieces broke off.

If the hypothesis is correct, then the further we go downstream, the rounder and smaller the rocks should be. Going upstream we should find that the rocks are more angular and larger. If we were patient we could also test the hypothesis by marking specific rocks and then checking back to see if those rocks have become smaller and more rounded as they moved downstream.

If the predictions turn out to be correct, we must still be careful about how much certainty to attach to our hypothesis.  Although our hypothesis might seem to us to be the only reasonable explanation, someone could argue that we have the mechanism wrong, and the rocks weren’t rounded by bumping into each other. If our experiment didn’t specifically check for the mechanism (e.g., by looking to see if chips fall off the rocks and the rocks are made smoother) then we would have to acknowledge the possibility.  We needn’t abandon the hypothesis as a useful tool for making predictions, but it is necessary to be open to the possibility that other things might be going on. If someone demonstrates conclusively that our hypothesis is wrong, then we have to discard the hypothesis and come up with a better one.

A good hypothesis is testable.  Someone might argue that an extraterrestrial organization creates rounded rocks and places them in streams when nobody is looking. There is no practical way to test this hypothesis to confirm it, and there is no way to prove it false. Even if we never see aliens at work, we still can’t say they haven’t been, because according to the hypothesis they only work when people aren’t looking. Compare this to our original hypothesis which allows us to make testable predictions such as rocks getting smaller and rounder downstream. Our original hypothesis gives us a way to see how realistic it is, whereas the alien hypothesis gives us no way to know if it makes sense or not.

# Theories and Laws

Two other terms appear in discussions of the scientific method: theory and law. A theory starts out as a hypothesis, but over a long period of time and a great many tests, it has never come up short. That doesn’t mean it never will, but the odds of that are very unlikely given our present (and conceivable future) state of knowledge.  You may have heard someone dismiss an idea by saying it is “just a theory,” but they are using the term incorrectly if they mean to say it’s a wild and unproven guess.

A law is a description of a phenomenon rather than an explanation of it.  For example, you could do thousands of tests by dropping an object with known mass and measuring its acceleration and the force with which it hits the ground.  Again and again your results will yield the formula force = mass x acceleration.  However, that doesn’t mean you know what is responsible for the force accelerating it toward the ground.  Yes, we say that gravity is pulling it toward the Earth’s surface, but why? A law is true regardless of why a phenomenon happens as long as it describes the outcome of that phenomenon.