Igneous, sedimentary, and metamorphic. Yes, it's the thee types of rocks. And here's a great video to introduce the young geologists in your class to the rock cycle.

Holocene, Pleistocene, Pliocene, Miocene, Oligocene, Eocene, Paleocene ... wait, did I miss one? PBS Digital Studios explains how human impact on Earth has potentially brought about a new epoch in geologic history, the Anthropocene....

Paul Andersen explains how soils are formed and classified. Weathering of rock creates particles which are mixed with water, air, and organic material. Soils are classified according to particle size, chemical makeup, and horizon...