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Download Fossils: Evidence of Past Life
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Fossils: Evidence of Past Life Different Types of Fossils • • • • • Petrified Molds and Casts Carbon Films Preserved Remains Trace Fossils Petrified: Turned to Stone • Arizona Minerals are absorbed by an organism’s tissues and replace cellular material. • Calistoga Molds (Hollow) versus Casts (Solid) • Mold: Organism is buried in sediment and then the organism is dissolved leaving only the outside shape in the rock • Cast: Organism is buried in sediment and the hollow space of the mold is filled in with mineral matter Carbon Films A film of carbon is left after all the liquids and gases of the buried organism are squeezed out Trace Fossils Indirect evidence of prehistoric life: Dinosaur Footprints Worm Burrows Extinct Reptile Stomach Stones Preserved Remains All or part of an organism preserved with little change Favored Conditions for Fossil Preservation 1. Rapid Burial: Sediment protects organism from being eaten or being decomposed by bacteria 2. Organism possessing hard parts Fossils and the History of Life • Principle of fossil succession: A time period can be recognized by its fossils • Theory of Evolution: Organisms reflect their environment since they, over generations, physically adapt to it Fossils are Useful to Geologists • Some organisms only existed at a particular time, therefore: specific fossils = specific age of rock • Some organisms only exist in a particular environment, therefore: specific fossils = specific environment Whiteboard Review 1. What type of fossil is the footprint of an ancient cat? 2. What is one thing that will help preserve an organism as a fossil? 3. If the same fossil is found in much different locations on the planet, what can this say about those locations?
