The simplest answer is that the Earth provides virtually all the resources used by human society from the rare earth metals needed to read these words on your screen to soils for growing food to aquifers that store water to aggregate for building roads. Perhaps the answer to why Earth's history is important is less clear. The Earth is very old (~ 4.7 billion years) and quite dynamic. Fortunately for us, that history is recorded, albeit sometime cryptically, in the upper few kilometers of crust. By studying the Earth's past we can learn how many of the resources we depend upon came to be and thus predict how they may or may not be renewable. For example, by learning how petroleum resources are formed, we can learn how long it may take for them to be replenished. By studying the evolution of biodiversity from the fossil record, we can learn how significant the current human-induced extinction is and over what time scales we can expect diversity to recover, if at all.
The most important thing I want my students to learn from my courses is how to think like and earth scientist. Students, regardless or their career path, need to understand what science is and how it's done. I try to accomplish this by having students conduct original research. Student projects are manageable within the allotted time, but they are comprehensive in that they involve developing a hypothesis, data collection, data analysis and communication of results. In the process students learn the difference between testable and non-testable hypotheses and the nature of uncertainty in scientific results.