1. Fossils and Geologic Time

2. What fossils are NOT…
My doctor says I’m in the early stages of fossilization!

3. What do you know? Is it a fossil?
These are cretaceous microfossils!
YES

4. Fossils?

5. Fossils…are:
Preserved remains or traces of an organism that lived in the past.
Fossils are formed when organisms die and are buried in sediment. Eventually the sediment builds up and hardens to become sedimentary rock.

6. Fossils…what are they for?
Interpreting Environments
• Fossils can be used to interpret and describe ancient environments.
trilobite
graptolites
gingko

7. Where do fossils form? What can become a fossil?
Specific conditions are needed for fossilization.
Only a tiny percentage of living things became fossils.

8. Kinds of fossils
1. Petrified - when minerals replace the remains and they become rock
2. Mold - when the shell remains and the contents dissolve (hollow)
3. Cast - when the mold becomes filled with minerals that are not a part of the original organism

9. PETRIFIED MOLD
CAST

10. So…fossil or not?

11. Intact Fossils
Sometimes whole animals become preserved intact, but this is very rare. If an organism is surrounded by ice or tar they might be discovered looking much the same as they did when they died.
AETOSAUR
FOUND IN THE NATIONAL PETRIFIED FOREST

12. Some remains can be preserved in ice…

13. Fossil Record
The dating of all fossils is included in the Geological Time Scale. This scale divides the time that the earth has existed into 4 eras.
* Eras are then divided into periods based on common events in that time period.

14. Geologic time

15. Relative Geologic Time Scale
The relative geologic time scale has a sequence of
eons
eras
periods
epochs
But only approximate numbers indicating how long ago each of these times occurred.

16. Let’s start at the beginning…
What would the rocks say if they could talk?

17. Pre-Cambrian
Began with the formation of the Earth 4.6 billion years ago.
Bacteria appeared 3.5 billion years ago, followed by algae and fungi.

18. Paleozoic Era Divided into 5 periods:
Cambrian period - Sponges, snails, clams and worms evolve
Ordovician period - First fishes evolved and other species become extinct
Silurian period - Land plants, insects and spiders appear

19. Devonian period - Amphibians evolve and cone-bearing plants start to appear.
Carboniferous period - Tropical forests appear and reptiles evolve.
Permian period - Seed plants become common and insects and retiles become widespread. Sea animals and some amphibians begin to disappear.

20. Next…The Big Guys…

21. Mesozoic Era
Divided into 3 periods:
Triassic period - Turtles and crocodiles evolve and dinosaurs appear.
Jurassic period - Large dinosaurs roam the world. First mammals and birds appear.
Cretaceous period – warm, reptiles, small dinosaurs and flowering plants appear.

22. As evolution occurred over time…
New species began to appear…

23. Cenozoic Era Divided into 2 periods:
Tertiary period - First primates appear and flowering plants become the most common.
Quaternary period - Humans evolve and large mammals like woolly mammoths become extinct.

25. So, In summary:

26. So, how do we sort out all of the fossils?

27. How do we know which fossils are from which part of the Geologic Time Scale?
1. Relative Dating
*Law of Superposition
*Index fossils
*Correlation of layers
2. Absolute Dating (Radioactive dating)

28. Relative Dating
Relative dating: looks at where the fossil is located to determine its age relative to other fossils. This only works if the area has been undisturbed.

29. Law of Superposition:
Nicolas Steno ( )
In an undisturbed succession of sedimentary rock layers,
the oldest layer is at the bottom
and the youngest layer is at the top
This method is used for determining the relative age of rock layers (strata) and the fossils they contain

30. Index fossils:
Index fossils can provide the relative age of a rock layer.
Existed only during specific spans of time
Occurred in large geographic areas
Index fossils include fusulinids and trilobites.

31. How do we know if we have the right fossils put together?...
Answer: Correlation of layers…

32. Relative age: Correlation
How is this done?
Faunal succession (correlation by fossils)
Fossil species succeed one another through the layers in a predictable order
index fossil
short-lived organism;
points to narrow range
of geologic time
fossil assemblage
group of fossils
associated
together

33. Correlation helps to determine the age of the fossils and their geologic time

34. Correlation: We can match up layers with similar fossils at different places by index fossils and comparison.

36. Absolute Dating
Uses radioactive elements near the fossils to determine the actual age of the fossils.
By determining the age of the radioactive element, scientists can calculate the age of the fossil buried nearby.
The absolute age of fossils is estimated by dating associated igneous rock and lava flows.