Geology is the science that studies both the makeup of and changes that happen to Earth. Unlike astronomy, physics, and biology, which can trace their origins back thousands of years, geology is a fairly young science that goes back only a few hundred years. As they develop their theories, geologists often draw information from other sciences such as physics, chemistry, and biology. Modern-day geologists use a great many high-tech tools to assist them in their work. In geology's early days, however, just about the only thing that scientists had to work with were rocks. To the untrained eye, rocks may not seem too exciting. In fact, even today,
What Makes a Scientific Theory?
To a scientist, the word theory means much more than a simple guess or idea. Before something can be considered a scientific theory, it has to go through many steps, a process known as the "scientific method." The scientific method begins with a series of observations that lead to a question about the way something works. Based on these observations, a scientist will then come up with one or more hypotheses to explain what is going on. Before a hypothesis can be considered a theory, scientists will design experiments to test the idea over and over again. During these tests, the hypothesis can be accepted, revised, or thrown out altogether.
Once they have finished their tests, scientists will report on the results of their experiments and get input from other scientists. Only after a hypothesis has stood up to all the experiments and testing, and after many scientists have accepted (or reached a consensus) that it is correct, can it be considered a scientific theory. As you will soon discover, the theory of plate tectonics has been tested over and over again, and even though it is relatively new, it has stood the test of time.
most people have a hard time telling one rock type from another. To a geologist, however, different rocks contain clues that help unlock the secrets of our planet's past. Questions about how Earth formed and how old it is can all be answered by "reading the rocks." Just like reading a book requires that you understand some basic rules about language, geologists follow some simple rules when they study rocks.
One of the first things that early geologists discovered was that not all rocks form the same way. One type of rock, called an igneous rock, forms from hot melted rock as it cools over time. Geologists call molten rock magma. Sometimes, as with a volcano, magma flows out over the surface of the Earth. When this happens,
the molten rock is called lava. Every minute of every day, somewhere on Earth, lava erupts from volcanoes to eventually form new igneous rocks.
Not all rocks come from magma. Sometimes, small pieces of broken rock called sediment get squeezed or cemented together to form a new rock. Since they are made from sediment, these "recycled" rocks are called sedimentary rocks. Sedimentary rocks usually form in water when layers of sand, silt, and clay pile up on the bottom. Sedimentary rock can also form on land, but not as often as they form in water. Sometimes, sedimentary rocks will trap the remains of living things in them. Objects like shells, footprints, and bones that are preserved in sedimentary rocks are called fossils. Fossils found in sedimentary rocks provide geologists with important clues about how life on our planet has changed over time.
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