FOSSILS!
What is a Fossil?
• A fossil is any evidence of prehistoric life.
• Must be older than 10,000 years but can be up
to billions of years old.
• Can be plant or animal.
• The history of the earth and ages of rocks can be
better understood by studying fossils.
• Question: What type of rock would most likely
have fossils?
• Answer: Sedimentary!
Life has changed
and become more
complex over time.
Studying fossils tells
us this.
Geologic Eras
• Paleozoic: Means “Ancient Life.”
• -Age of Fishes
• -Cambrian Explosion (life evolved at an alarming rate during this
period)
• -Ended with Permian-Triassic Extinction
• Mesozoic: Means “Middle Life.”
• -Age of Reptiles or Age of Dinosaurs
• -Mammals appeared at this time.
• -Ended with Cretaceous-Tertiary (K-T) Extinction. Likely from a
meteorite impact. (Chicxulub impact crater in Mexico).
• Cenozoic: Means “New Life.”
• -Age of Mammals
• -Evolution of Humans
Virginia’s Fossils
• Fossils mainly found in Coastal Plain, Valley and Ridge, and
Appalachian Plateau provinces.
• Most Virginia fossils are marine organisms.
• Question: What does this mean about Virginia’s past
environment?
• Answer: Virginia has been covered by seawater for much of
its history.
• Question: Paleozoic, Mesozoic, and Cenozoic fossils are found
in Virginia. What does this tell us?
• Answer: Virginia has been around since the Paleozoic Era.
Conditions for making a fossil
• 1.) Quick burial: Prevents organism’s
remains from being weathered and
eroded or consumed by other
organisms.
• 2.) Hard Parts: Organism usually must
have hard parts such as bone, teeth,
or shell that won’t be eaten or won’t
rot.
Types of Preservation
• 1.) Unaltered Remains: Original organism or hard parts are
preserved either in ice, amber, or tar pits.
• 2.) Petrified/Replacement by permineralization (Turned to
stone): Original material is replaced with another mineral.
• 3.) Mold (Cake Pan): For example, a shell presses into soft
sediment leaving an impression. Shows you outside parts.
• 4.) Cast (Cake): If the mold is filled in with sediment. Shows
you inside parts.
• 5.) Carbonized (thin and delicate): Anoxic environment.
Burgess Shale. Can preserve soft parts (i.e. insects/feathers).
• 6.) Impression (shallow mold)
• 7.) Trace: Fossils of tracks, burrows, coprolites (poop).
Principle of Faunal Succession
• States that fossils aren’t randomly placed in strata, but rather
follow a succession where they succeed each other in a
definite and determinable order.
• Organisms live for a certain amount of time and then go
extinct, so we can use them to tell us age of rocks.
• Index Fossils: A good index fossil is is widespread but shortlived.
• Certain Trilobites are good index fossils.
Fossil Correlation
• Fossils can be used to
correlate strata
hundreds of miles
apart.
• If an index fossil is
found in two different
rock layers, we know
they must be the same
age.
• We can then correlate
or connect them
together.
Fossil Correlation Lab
•Start today and finish next
class.