Introduction
Greetings from Indiana! Back in the Ordovician and Silurian time period, Indiana was covered by a shallow sea and located in a tropical climate—much like the Bahamas of today seen in this photo (USGS).
200 million years ago if you wanted to travel to Africa or France, you could have done so by means of a 14-hour drive from Indiana. Why? Well, all the continents were connected to each other at that time. You are about to learn two of the key concepts of geology: geologic time and plate tectonics. Both of these ideas drive the thinking behind studies of geologic events, earth processes, and the rest of modern earth science. We’ll discover why you cannot drive to Africa today (well at least that’s what they tell me) and why you better be wearing your swimsuit if you lived in Indiana 400 million years ago.
As you learned in the last section, the idea of “geologic time” was coined as early geologists separated their views from the time line people derived from Western religion. Geologic time is no different from the time shown on your watch or cell phone—it’s the vastness of geologic time that is difficult for humans to grasp. You will learn how to imagine geologic time, learn the rates of geologic processes, and discover the geologic time scale.
Unlike geologic time, plate tectonics is a more recent theory to science—a theory not totally accepted until the mid 1970s. Plate tectonics, the theory that the earth’s crust is made out of moving plates, was discovered based on good old-fashioned rock collecting, along with data collected from modern and sophisticated equipment. It’s pretty hard to imagine the continents and oceans are moving around (it makes believing in UFOs seem simple)—so I’ll give you the “mountains” of evidence that support the plate tectonics theory.