2. Molds and Casts  A mold is a hollow space left in a rock by an object that has dissolved in it  If this mold fills in with mud or minerals, the filling can harden, resulting in a cast

3. Formation  An organism dies and lands in soft sediment  The sediment becomes rock over time  Water seeps into the rock, decaying/dissolving the organism, leaving a mold  Minerals fill the mold and create a cast of the organism

4. Conditions  Water – decays the organism  Sedimentary rock – layers over the top of the dead organism. Other types of rock don’t layer and couldn’t form a mold