From a scientific point of view, rocks are essential trace fossils. A trace fossil is a type of imprint that reflects an animal's behavior. Some of this behavior is imprinted on fossilized rocks. In this respect, rocks become a record of time, something that can be used to construct understandings of the past, conceptions of how things were, and help to bridge the idea of who we were to who we are. The use of fossilized rocks tells us much because it is the result of pressure plus time, a critical element of geology, in general. Rocks demonstrate this. Hence, to study geological understandings as expressed through rocks give us invaluable information about the past in "real time," through the fossil process.
Good question. Why would anyone study rocks? Well, if we probe a little deeper, there are some reasons why people should study rocks.
When people want to learn about the past, they are immediately handicapped, because the past does not always leave records of what it was like. So, scientist and historian need to use whatever there is. In some cases, the only thing to study is rocks. And if a person studies these rocks and compares these rocks with other rocks, there can be some great insights. For example, the study of rocks can tell you, about past temperature, how thick the atmosphere was at a given time, whether there was a body of water, or a volcano, or perhaps something else. Rocks can even tell you about past in greater detail, if things like fossils are on these rocks. You might say that rocks are clues to the past.
If you're talking about why it's important for someone in high school to study rocks, I'd say it's because you need to be exposed to a little of everything (in terms of academic subjects) in high school. When I was in high school, at least, I had no idea what I wanted to do or be. Studying a little bit of everything at least gave me some ideas about that.
It's also nice to know at least something about a lot of things just for your own personal growth. I enjoy knowing a little about a lot.
If you're talking about a higher level, geology is pretty important (it's important that someone should know about it). If no one did, we wouldn't know much about finding oil or about what places are going to be most affected by earthquakes or about why/how landslides happen, for example.
Rocks to a geologist are like a map to a traveler. By studying rocks scientists have been able to learn much about a planet. They provide clues to our planet's past from which certain conclusions can be drawn and predictions can be made. The rock cycle is as important to the well being of our environment as the water cycle. The breakdown and layers found in rocks are able to tell scientists the weather/ climate patterns of previous eras. Rocks help scientists determine how lands were formed. In addition they show man how water patterns have changed as well as regional adjustments such as areas that were previously underwater have now become deserts. They hold clues to life in previous times. The layers of rocks have trapped dead animals and plants enabling scientists to have historical records of previous life.
By studying the past scientists are able to determine precautions they need to take to protect our environment. With the current concerns over Global Warming, scientists are using rocks to determine how to reduce further damage. The most important reason that rocks should be studied is that they offer a mirror into the past that can be used to help us have a better future.
Rocks from other planet have also been brought back during space explorations and like rocks on earth are revealing mysteries about other planets atmospheric, land, and environmental changes.