The first step in becoming a fossil is death. Natural causes, such as predation or disasters could have killed creatures that lived long ago (just as it happens today). The second step involves the animal being buried in sediment, preventing it from being eaten by scavengers or decomposed by bacteria. However, certain organisms are more likely to become fossils because of what paleontologists call the preservation bias. This means that not all animals are going to be preserved, and there are conditions that allow for easier preservation than others. Animals with hard parts are more likely to be preserved than animals that have soft bodies. Aquatic animals are more likely to be preserved than terrestrial animals because water ecosystems have greater preservation potential. Preservation potential increases in aquatic environments, low oxygen environments and locations with high sedimentation rates. [Some aquatic ecosystems (like Fossil Lake) have a greater preservation potential than others. Fossil Lake is thought to have been density stratified like an estuary. Heavier (more dense) salt water occupies the deepest sections of the lake and lighter (less dense) freshwater ‘floats’ above in the shallows (a remnant of an evaporative phase when the lake was young). This prevents freshwater scavengers from eating dead animals that fell to the bottom of the lake. Lake turnover (where anoxic waters at the bottom mix with oxygen rich water near the surface) did not occur, creating perpetual anoxic conditions along the bottom which discouraged scavengers]. Once an animal dies in a place where preservation is likely, it becomes buried in sediment and protected from scavengers and bacteria. The examination of the second step (what happens after death and how animals become fossils) is considered the science of Taphonomy, discussed below. The Fossil Cycle - Teachers (U.S. National Park Service) Begin by handing out the ‘Fossil Cycle Reading’ and have the students read it through to provide background for the activity. Students number a piece of paper 1 – 15. This is their ‘travel log’ where they record their journey. Students are assigned a station to begin with (plant, animal or detritus). This is determined by flipping a coin, drawing popsicle sticks or at the teacher's discretion. The first station is recorded as number 1. Students line up at the station and take turns rolling the dice. They record the roll on their log sheet and move to the next station. If they obtain a roll that instructs them to remain at the same station, they move to the back of the line for another chance to roll. Once the students have completed 15 turns or became a fossil, the game is over and they return to their seats. Mold and Cast – a type of fossil where the original material has been replaced by stone and the impression is left behind. A mold is the ‘negative’ and cast the ‘positive’. Skip to footer.