Transcript Fossils: Evidence of Past Life

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?