Students should develop the ability to refine and refocus broad and ill-defined questions. An important aspect of this ability consists of students' ability to clarify questions and inquiries and direct them toward objects and phenomena that can be described, explained, or predicted by scientific investigations. Students should develop the ability to identify their questions with scientific ideas, concepts, and quantitative relationships that guide investigation. Water evaporates from the earth's surface, rises and cools as it moves to higher elevations, condenses as rain or snow, and falls to the surface where it collects in lakes, oceans, soil, and in rocks underground.
Society relies on the water cycle to deliver water for all kinds of uses.
But people have almost no control over how much or how little water we get. Whether they live near a rainforest or in a desert, planners need to understand the hydrological cycle to create drought-resistant communities. The earth processes we see today, including erosion, movement of lithospheric plates, and changes in atmospheric composition, are similar to those that occurred in the past. Earth history is also influenced by occasional catastrophes, such as the impact of an asteroid or comet. Tree-ring data shows that within the past 2,000 years, portions of what is now the western United States experienced at least two droughts that lasted for more than a century at a time.