Petrified Fossils
Molds and Casts
Carbon Films
Preserved Remains
Trace Fossils
Petrified Fossils - How do they form?
Mineral rich water soaks into cracks and crevices
Minerals “precipitate” and fill the spaces
Mineral replace the solid material of an organism
Molds and CastsHow do they form?A shell or other structure is buried in sediment and then
dissolved by water
Mold reflects the shape and surface markings
Cast fossils form when the hollow spaces of a mold are filled with minerals
Carbon FilmsHow do they form?Organism is buried under fine sediment
Pressure squeezes out liquids and gases, leaving behind a thin film of carbon
Show fine details of the organisms structure
Preserved Remains
How do they form? Frozen in permafrost Preserved in amber Preserved in tar
Trace FossilsHow do they form?Tracks left in soft sediments that later harden
Burrows made by animals in sediment, wood or rock that later fill with minerals
Fossils of dung and stomach contents
Conditions for Fossilization
1. Rapid burial
2. Possession of hard parts
History of Life on EarthFossil Succession - each layer has a distinct set of fossils; progress in a definite order
Theory of Evolution – life changes over time from simpler to more complex organisms
Natural Selection: individuals that are better adapted to the environment are more likely to survive and reproduce
Adaptations: traits that affect an organisms ability to survive
Interpreting the Fossil Record
Correlate rock layers Index fossils – geographically widespread and
abundant; existed for a limited time Groups of fossils to establish relative age
Reconstruct past environments Use adaptations of fossils to get clues about
the environment they lived in