Fossils Ex-Life

What are Fossils? Remains of past life Two types: Altered remains Unaltered remains

Unaltered Remains Remains that haven’t changed over the years. “hard parts” Examples: Teeth Bones Shells Whole organisms (under special circumstances)

Petrification Altered Organism turns into stone Often with trees (cells replaced with silica by water) Creates an exact replica

Molds and Casts Altered Mold: indent Cast: raised Mold holds the shape of the object and the cast is the reverse

Carbonization Altered Only happens in fine sediment Organism is pressed and liquids and gases are squeezed out Only a thin film of carbon is left Lots of details!

Amber Fossilized tree sap Flows over organism and hardens Protects delicate organisms DOESN’T ALTER ORGANISM (unaltered remains)

Indirect Evidence AKA trace fossil Any evidence of past life that is not an actual life form Examples: Footprints and tracks Burrows Gastroliths Coprolites

Fossil Preservation 2 conditions are necessary: William Smith Rapid burial Decomposition Scavengers Hard parts More resilient William Smith Fossils can be used in geology Why?

Fossil Succession Fossils are found in a specific order Any period of time can be identified by its fossils Order: Age of Trilobites Age of Fishes Age of Coal Swamps Age of Reptiles Age of Mammals

Index Fossils Requirements: Widespread geographically Short period of time (geologically) Large numbers