1. Geologic Time

2. Geologic Time How long ago did the dinosaurs live?
How old is the grand canyon?
How old is the Earth?

3. Fossils
Definition
The preserved remains or traces of living things.

4. Fossils Fossils are mostly found in sedimentary rock Why?
Can they be found in other types of rock?

5. Five Kinds of Fossils
Petrified Fossil
Mold and Cast
Trace Fossil
Preserved Remains
Carbon Films

6. Petrified Fossils
Fossils in which minerals replace all or part of an organism

7. 4 Stages of Petrified Fossil Formation
1. Death
The organism dies

8. Organism is covered by sediments.
2. Deposition
Organism is covered by sediments.

9. 3.Permineralization
The chemicals in the organism’s body parts are slowly changed to minerals such as calcite, iron or silica.

10. 4. Erosion
Weathering and Erosion expose the fossil at the Earth’s surface.

11. Molds and Casts
Mold- A hollow area in sediment in the shape of an organism.
Casts- A copy of the organism made from the mold filling with minerals.

12. Carbon Film
A type of fossil consisting of an extremely thin coating of carbon on rock.

13. Trace Fossil Ex. Foot prints, worm burrows, coprolites
A type of fossil that provides evidence of the activities of ancient organisms
Ex. Foot prints, worm burrows, coprolites

14. Preserved Remains
Remains of ancient organisms that have not decayed.
Ex. Frozen mammoths, Saber tooth cats stuck in tar pits, Insects in Amber

15. What does the fossil record tell us?
Organisms change over time
Organisms go extinct
The Earth’s environment changes over time
Changing climate
Changing landscape

16. The age of a rock compared to rocks around it
Relative Age
The age of a rock compared to rocks around it

17. Law of Superposition
The geologic principle that states in undisturbed horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it.

19. Clues from igneous rocks
Extrusions- rock layers below extrusions are always older.
Intrusions- Intrusions are always younger than the rock around and beneath it.

21. A fault is always younger than the rock it cuts through.
Clues From Faults
A fault is always younger than the rock it cuts through.

23. Gaps In the Geologic Record
Unconformities are gaps in the geologic record due to erosion

24. Index Fossils Must be widely distributed.
Must have existed for a short period of geologic time.
They are used to get the absolute age of the rock they are in.

25. Absolute Age
Absolute age is the number of years since the rock was formed.
Absolute age is found using radioactive dating.
It is found by using the half life of radioactive elements in the rock.
Can only be used for igneous rocks.