This Topic in Depth explores the world of frozen soil, including permafrost and tundra. The first site is provided by the Missouri Botanical Gardens Web site, entitled Tundra (1). This kids focused site does a good job of clearly explaining what tundra is, where it's located, and what types of plants and animals are found within tundra areas, as well as offering a photo gallery. The second site, Permafrost (2), is a lesson plan that teaches kids about freezing and thawing soil. Maintained by Newton's Apple television show's companion Web site, teachers are given a complete activity description including vocabulary, additional resources, and instructions for completing the lesson plan. The next site, from the PBS Denali Web site, is another Activity for the Classroom called Permawhat? (3). Objectives of the lesson include having students identify the contents of permafrost found in Alaska's Denali Wilderness, creating their own permafrost in the classroom, comparing summer and winter permafrost, and finally experimenting with the results of warming permafrost. The fourth Web site, A Year in the Life of Your Soil (4), is offered by the University of Minnesota Extension. The single-page site explains what physically happens to soil over a one-year period due to climatic conditions. For example, during the winter, surface soil may freeze and thaw several times, but subsoil only freezes once. Other topics covered include structure, temperature, nutrients, organisms, and plant activity. The next Web site from the US Geological Survey is called Earth Science Photographs (5). The collection of twelve permafrost pictures are from various areas within Alaska, and show some of the interesting effects that the freezing and thawing of soil has on surrounding landscapes. From the National Snow and Ice Data Center, the Permafrost: Insights From a New Northern Hemisphere Map (6) Web site offers some unique information. Visitors will find a description, a map, and a graph that explain the extent of permafrost toward the north pole. The seventh site, Tundra: The Not-So Barren Land (7), is maintained by UC Berkley's Museum of Paleontology. The one-page site explains the general characteristics of a tundra biome and what the difference is between arctic and alpine tundra. The last offering is from the US Fish and Wildlife Service called Active Layer at the Soil Surface (8). The site focuses on the thirteen steps of freezing and thawing that tundra soil experiences. Each step is illustrated and explained from spring to winter, and the entire process is shown as an animation at the bottom of the page.