Watching Old Faithful transform from a smoldering mound to an explosive 50-meter high geyser is enough to generate awe in any observer. Behind this stunning, visual geologic display is a triad of heat, water, and plumbing that rarely unify on our planet. But geologists are not the only scientists drawn to geysers. Biologists have recently recognized thermal features as a habitat of interesting bacteria that thrive in extreme conditions and may provide clues to the origin of life. Engineers tap into the steam and hot water found in thermal areas around the Pacific Rim to generate electricity without releasing the carbon dioxide associated with fossil fuels. Geysers provide an excellent opportunity to explore the Earth system as described by the National Science Education Standards (content standard D for grades 5?8). By using the geyser model activity described in this article, students can investigate the relationship between the hydrosphere, geosphere, and biosphere. In addition, students will be able to develop descriptions, explanations, and predictions using the model as a guide for their exploration and apply their thinking to their local setting. (Contains 2 figures.)