1. Notes on
Fossils (from top left) are of a ammonite (marine); T-Rex; an ancient fish and a trilobite (marine).
Earth/Space

2. S.W.B.A.T.
List the conditions necessary for fossils to form
Describe several processes of fossil formation
Explain how fossil correlation is used to determine rock ages

3. Fossils are evidence of past life on Earth
Fossils are remains, imprints or traces of prehistoric organisms
Extinct animals are studied using their fossilized remains
Students frequently ask if fossils are worth money. Common fossils are not worth very much – even if they are
very old. Some examples of common fossils include mollusks, flints, ammonites and shark teeth. Rare fossils –
such as a near-complete skeleton of a T-Rex – may go for millions of dollars!

4. Ammonite Fossils – Extinct Since the Dinosaurs
Ammonites were an important group of marine mollusks that were numerous in the Earth's oceans for
360 million years, from about 425 million years ago, during the Silurian period, to 65.5 million years ago,
when they went extinct along with the dinosaurs and many other species.

5. Fossils can also tell how a species lived; reproduced and died
Most organisms decay very quickly after death
Microorganisms such as bacteria cause remains to rot
While we can easily recognize and identify some fossils, many fossils represent animals that no longer
exist on Earth. We only know about extinct groups like dinosaurs, ammonites and trilobites through fossils.

6. Soft parts (tissue, feathers and hair) do not fossilize easily
Fossils
Soft parts (tissue, feathers and hair) do not fossilize easily
Hard parts (teeth, shell & bone) tend to preserve well over time
Pictured is of a large fossilized shark’s tooth. Shark’s teeth are common because they preserve well and a
single shark may produce thousands of teeth during its lifetime.

7. Fossils
Animals or organisms covered by sediment quickly after death also preserve well
Scavengers (usually) do not eat hard parts & cannot scavenge what is buried
Even if plants or animals become fossilized, permanent preservation after being buried for eons is not necessarily
guaranteed. Often, sedimentary rocks become metamorphosed, or altered due to the tremendous heat and
pressure. The Volcanic activity that was regionally so prevalent in the Jurassic and Cretaceous cooked many
fossils in sedimentary rocks, and the forces involved in mountain building often compressed fossils in to
meaningless smudges in the rock, into nothing at all.

8. Types of Preservation
Permineralized – remains that have been buried & replaced by minerals in groundwater
Pictured (left) petrified wood; right is an ammonite fossil that has been changed or permineralized to pyrite –
very rare! The permineralization process is very slow. It happens as water seeps through the sediment
that covers an organism; the sediment helps keep the organism intact, and the mineralized water slowly
works its way into the remains. Depending on the type of minerals involved and the conditions,
petrification may result in incredibly detailed preservation, allowing people to differentiate individual
cells in the organism, or it may create a more rough cast.

9. Types of Preservation
Carbon film - organisms are buried by sediment then slightly heated & squeezed
A thin film of carbon residue is left “silhouetting” (or shadowing) the original organism
When a dead organism is buried, sediment may pile up. The organism's remains are subjected to heat and
pressure. These conditions force gases and liquids from the body. A thin film of carbon residue is left,
forming a silhouette of the original organism which is called a carbon film.

10. Molds – buried hard part dissolves in the sediment leaving a cavity
Types of Preservation
Organisms with shells or other hard parts may form impressions in soft mud or sand
Molds – buried hard part dissolves in the sediment leaving a cavity
Pictured is a trilobite cast (top) and its subsequent mold (bottom). Trilobites (meaning "three lobes") are a
well-known fossil group of extinct marine arthropods that form the class Trilobita. Trilobites form one of the
earliest known groups of arthropods beginning around 512 million years ago – extinction about 250 million
years ago.

11. Types of Preservation
Later, mineral-rich water or other sediment may enter the cavity (or mold)
Cast – when the sediment-filled mold is hardened into rock making a copy of the original organism

12. Types of Preservation
Original remains – tar, amber & ice can preserve original tissue of an organism
Sometimes original remains & the DNA of the animal is also preserved (ex. Dinosaur bones)
Picture shows insects that became trapped in tree sap that eventually became amber. Original remains also
includes unaltered hard and soft parts: mummification, freezing, encasement in amber (fossilized tree sap).
Very very rare; usually only very young fossils.

13. T-Rex Femur Bone Found to Have Original DNA
FAQ – Can we bring back the dinosaurs? If we could find perfectly preserved dinosaur DNA, extract and sequence
it with little error, organize it into chromosomes, place it into the living egg of the correct species (wait...that would
mean we already had the egg and its own DNA!), and raise the egg successfully, then we could all have pet
Triceratops – highly unlikely!

14. Trace – fossil trails, burrows & footprints that have hardened in rock
Types of Preservation
Trace – fossil trails, burrows & footprints that have hardened in rock
Rock was once silt/mud or a volcanic ash layer before solidifying
Because they’re so common--especially compared to complete, articulated dinosaur skeletons--dinosaur footprints
are an especially rich source of information about the size, posture, and everyday behavior of their creators.

15. Which Dinosaur Made These Tracks?
Video (1:42) “Dinosaur Tracks Uncovered in Arkansas”
Except in extraordinary circumstances, it's pretty much impossible to identify the specific genus or species of
dinosaur that made a given footprint. What paleontologists can figure out fairly easily is whether the dinosaur
was bipedal or quadrupedal (that is, whether it walked on two or four feet); what geological period it lived in
(based on the age of the sediment where the footprint is found); and its approximate size and weight (based
on the size and depth of the footprint).

16. Types of Preservation
Index fossils – tells exactly where & when a species existed (ex. Graptolites)
Index fossils can be used to determine the ages of the rock layers they are found in
Fossils also tell us about ancient environments & shallow seas (ex. Crinoids)
Index fossils are also the fossil remains of an organism that lived in a particular geologic age – and used to
identify or date the rock or rock layer in which it is found. Also called guide or zone fossils.

17. Relative Dating and Index Fossils
What is relative dating?
Any method of determining whether an event or object is older or younger than other events or objects.
What is an index fossil?
A fossil that is found in the rock layers of only one geologic age and is used to establish the age of the rock layers.
Is found in rock layers
around the world, ex Trilobites

18. Class Activity
Explain how some wooly mammoths have been found preserved intact in frozen ground
What type of fossil preservation occurred and what conditions must have persisted since these animals went extinct?
As global warming thaws the ground in Russia, researchers have been making some amazing finds. Now, Russian
researchers claim to have made what could be the most incredible discovery of all: the preserved blood and meat
of a woolly mammoth. Part of the animal became covered by a frozen pool of water about 10,00-15,000 years ago,
allowing its tissue to remain better preserved than any other mammoth that they've found.