It is important that your students begin to understand that rocks are made of minerals. Different rocks have different characteristics because of their minerals, the ways in which the rocks were formed, and the processes that acted on the rocks since they were formed. In this first investigation, your students will use their senses to investigate some of the physical properties of different types of rocks. They will then use their observations of the rocks to identify a particular rock from a collection.
In the previous investigation, students discovered that living things can die and decay. Soft parts are more likely to decay than hard parts. For this reason, the most common fossils are bones, teeth, shells, and the woody stems of plants. For a fossil to form, an organism must be buried quickly so that any oxygen is cut off and its decay slows down or stops.
It is very likely that any organism on Earth will be either eaten by scavengers or decomposed by microorganisms after it dies. Organisms decompose more quickly when they are in contact with oxygen. Most environments exposed to the open air are in contact with plenty of oxygen, so the soft tissues of dead organisms, whether plants or animals, decay quickly. Many, if not most, underwater environments also have a lot of oxygen, since water can dissolve oxygen from the atmosphere.
