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 changedand become morecomplex over time.

Studying fossils tellsus 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 short-lived.

• 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.