The planet looks a lot different than it did when it formed four and a half billion years ago. The force of erosion, the slow wearing away of the land, has never ceased. Erosion can make slow, almost invisible modifications, or sudden, drastic alterations of the landscape. Either way, the forces of erosion will always be at work giving the Earth a facelift. The DVD has extra features: fully indexed "chapters" correlated to national science standards, interactive glossaries and quizzes, bonus footage of never-before-seen segments, interviews and demos, Spanish translation, and on-disk implementation guide. .